Keywords To Remember
Electricity & Components
- Electric current
The flow of electric charge (usually carried by electrons) through a conductor such as a wire. - Battery
A device that converts chemical energy into electrical energy, made by combining multiple electric cells. - Electric cell
A single unit that generates electrical energy from chemical reactions. - Circuit
A complete and closed path through which electric current flows. - Conductor
A material that allows electric current to pass through easily, such as copper or aluminum. - Insulator
A material that does not allow electric current to pass through, such as rubber or plastic.
Heating Effect of Current
- Heating effect of electric current
Heat generated in a conductor when electric current flows through it, due to the resistance of the conductor. - Resistance
The property of a material to oppose the flow of electric current, causing the generation of heat. - Joule’s Law
A law that states the heat produced in a conductor is directly proportional to the square of the current, resistance, and time. - Nichrome
An alloy of nickel and chromium, commonly used in heating elements because of its high resistivity and melting point. - Heating coil
A wire, typically made of nichrome, used in electrical appliances to convert electric energy into heat.
Safety Devices
- Electric fuse
A safety device made of a thin wire that melts and breaks the circuit when the current exceeds a safe level. - MCB (Miniature Circuit Breaker)
An automatic switch that turns off the electrical circuit when the current exceeds the safe limit. - Overloading
The connection of too many electrical devices to a single circuit, causing excessive current flow. - Short circuit
A fault in an electrical circuit where current flows through an unintended low-resistance path, often leading to overheating and fires.
Magnetic Effect of Current
- Magnetic effect of electric current
The property of a current-carrying wire to produce a magnetic field around it. - Electromagnet
A temporary magnet created by passing current through a coil of wire wrapped around a soft iron core. - Solenoid
A cylindrical coil of wire acting like a magnet when carrying electric current; often used to create controlled magnetic fields. - Armature
A movable iron piece in devices like electric bells that is attracted to the electromagnet when current flows. - Electromagnetic induction
The process of generating current in a conductor by changing the magnetic field around it (related concept but not deeply covered here).
Applications
- Electric bell
A device that uses the magnetic effect of electric current to create sound by striking a gong repeatedly. - Electric iron
A device that converts electric energy into heat energy to press clothes. - Electric stove
An appliance that uses the heating effect of electric current to cook food. - Room blower
A device that uses both heating and mechanical effects of electric current to blow warm air. - Loudspeaker
A device that converts electric signals into sound using an electromagnet and diaphragm. - Telephone diaphragm
A thin membrane in phones that vibrates in response to electric signals, producing sound.
Something To Know
A. Fill in the blanks.
- When current is switched on, an electric fan converts ___________ energy (mainly) into ___________ energy.
Answer – electrical, mechanical
- When current is switched on’ in a room heater, it converts ___________ energy into ___________ energy.
Answer – electrical, heat
- We prefer a wire of ___________ for making the ‘heating element’ in domestic appliances like the electric iron, electric heater and the electric toaster.
Answer – high resistivity and high melting point
- A safety device, based on the heating effect of current is the ___________ .
Answer – fuse
- Electromagnet should show rapid ___________ when the current is switched ___________.
Answer – magnetisation, off
B. Write True or False for the following statements.
- An electric current can produce a heating effect but not a magnetic effect.
Answer – False
- The heating coils/elements of different electrical appliances are usually made from copper or aluminium wires.
Answer – False
- When the current through a fuse wire exceeds its specified value, the fuse wire melts and breaks.
Answer – True
- Connecting many devices in a single socket is not likely to cause any problem in a circuit.
Answer – False
- The strength of an electromagnet can be increased by decreasing the number of turns of its coil.
Answer – False
C. Tick (✓) the correct option.
- When electric current flows through a filament of electric bulb, the filament gives out-
heat energy only
both heat and light energy
light energy only
chemical energy
Answer – both heat and light energy
- A fuse wire is a wire of—
high resistivity and low melting point.
high resistivity and high melting point.
low resistivity and low melting point.
low resistivity and high melting point.
Answer – high resistivity and low melting point
- We are more likely to observe a strong magnetic effect with a—
current carrying straight wire.
current carrying circular coil of many turns wound on a soft iron core.
current carrying coil of many circular turns.
current carrying circular coil of a single turn.
Answer – current carrying circular coil of many turns wound on a soft iron core
- A common household device, that uses an electromagnet in its working, is—
the electric bell
a room heater
a geyser
the tube light
Answer – the electric bell
- A good electromagnet would—
act like a magnet when the current is ‘ON’ but would not do so when the current is ‘OFF’.
not act like a magnet when the current is ‘ON’ but acts like one when the current is ‘OFF’.
act like a magnet both when the current is ‘ON’ or is ‘OFF’.
not act like a magnet both when is current is ‘ON’ or is ‘OFF’.
Answer – act like a magnet when the current is ‘ON’ but would not do so when the current is ‘OFF’
D. Answer the following questions in brief.
- The bulb in the circuit shown in figure docs not glow. Why? Redraw the circuit diagram by making the necessary changes in it, so that the bulb starts glowing.
Answer – Corrected Circuit Diagram:
Here’s how you should redraw the circuit:
- Keep the bulb and switch in the same positions.
- Change the orientation of one battery cell so that one terminal is positive (+) and the other is negative (–).
- This will ensure a complete closed circuit with a potential difference.
- Name three practical devices based on the heating effect of current.
Answer – Three practical devices based on heating effect of current:
Electric iron
Electric heater
Electric toaster
- Write two special characteristics of the wire needed for making the ‘element’ of an electric heater.
Answer – Two characteristics of wire for heater element:
High resistivity
High melting point
- Give the meaning of the terms ‘short circuiting’ and ‘overloading’ in an electric circuit?
Answer – Short circuiting: Occurs when live and neutral wires touch, creating a low resistance path.
Overloading: Happens when too many devices draw current from one socket.
- Do you think an electromagnet can be used for separating plastic bags from a garbage heap? Explain.
Answer – Electromagnet use in garbage separation: No, because electromagnets attract only magnetic materials (like iron), not plastics.
- State any three applications of an electromagnet.
Answer – Three applications of an electromagnet:
Electric bell
Electric crane for lifting scrap iron
Magnetic relay switches
E. Answer the following questions
- The same amount of current flows through the connecting wires and the bulb filament. However, it is only the filament that glows. Why?
Answer – Only the filament glows because it has high resistance, so it gets hot enough to emit light, unlike the connecting wires.
- The brightness of light, emitted by a bulb, is observed to decrease when an electric heater is connected in series with it. Suggest the likely reason for this observation.
Answer – Heater in series decreases bulb brightness as it increases total resistance, reducing current flow through the bulb.
- Suggest an experimental set up to illustrate the action of an electric fuse.
Answer – Experimental setup for electric fuse:
Connect a battery, fuse wire, and a bulb. Increase the current (using more cells or reducing resistance). The fuse will melt when current exceeds safe level.
- A novice electrician, while carrying out some repairs in Sumit’s house, tried to put a piece of tungsten wire in a ‘fuse’. Sumit’s father, on noticing this, stopped him from doing so. Give reasons as to why he did that.
Answer – Why not tungsten in fuse?
Tungsten has a high melting point and won’t melt quickly in case of excess current, making it unsuitable as a fuse.
- Draw a labelled diagram of an electric bell and explain its working.
Answer – Diagram and working of electric bell:
Labelled parts: Electromagnet, iron armature, hammer, bell, contact screw, switch, battery.
Working: When current flows, electromagnet attracts armature, hammer strikes bell, circuit breaks, armature returns, and cycle repeats rapidly.
Value Based Question
The school principal, in her morning address, urged the students to work in a hard, dedicated and focused way. She also advised the teachers, seniors and parents to go a ‘little out of their way’ to guide those who need a ‘little extra help’.
Mohan, on returning home, discussed the principal’s comments with his grandfather. The grandfather told him that the principal’s suggestions were very good. These suggestions, if followed, can increase the student’s strength, and capability, in the same way as appropriate adjustments can help increase the strength of an electromagnet.
- State any two of the values that the principal urged her students to develop in themselves.
Answer – Two values urged by principal:
Dedication
Willingness to help others
- Write two factors that can be adjusted to increase the strength of an electromagnet.
Answer – Two ways to increase electromagnet strength:
Increase number of coil turns
Use stronger current or soft iron core
- Share, with your friends and classmates, any incidence in which you went ‘a little out of the way’ to help/guide someone.
Answer – Personal example: (Write your own)
“I once helped a friend who was struggling in math by tutoring them every evening for a week before exams.”
Something To Do
- Collect data about the maximum current rating of domestic appliances like an electric mixer, television set, washing machine, toaster, electric oven, etc. With the help of your teacher/electrician, find out the type of fuse used for their safety.
Answer – Current ratings and fuse types (sample):
Mixer: ~5A – fuse of 5A
TV: ~2A – fuse of 3A
Washing machine: ~10A – fuse of 15A
(Confirm with teacher/electrician)
- Take out the parts of an old and ‘out of use’ electric bell, or a telephone, or a toy working with cells/battery. Is an electromagnet used in them? Discuss and record your findings.
Answer – Disassembled devices:
Electric bell: Yes, has an electromagnet
Old telephone/toy: Often have electromagnets (e.g., in speakers or ringers)
- Make an electric circuit consisting of an electric switch, two electric bulbs and a battery (three cells of 1.5 Volts each). Connect the switch between the two bulbs. Does any of the bulbs glow when the switch is in the ‘OFF’ position? Is there an order, in which the bulbs glow when the switch is in the ‘ON’ position?
Answer – Circuit with switch and bulbs:
Switch OFF: No bulb glows
Switch ON: Both bulbs glow (simultaneously if connected in series)
- In the Activity 2, use (i) nichrome wires of longer lengths but of same thickness; (ii) nichrome wires of same length but of different thickness. Switch on the circuit. Observe the change, if any. Try thinking of an explanation for your observations.
Answer – Nichrome wire activity:
Longer wire: Less glow (higher resistance)
Thinner wire: More glow (higher resistance)
Reason: Resistance depends on length and thickness of wire
Additional Questions And Answers – 01
Fill in the Blanks Questions and Answers:
- A material that allows electric current to pass through it easily is called a ___________. Answer: conductor
- A ___________ is a coil of wire used to produce a magnetic field when electric current passes through it.
Answer: solenoid
- In a fuse, the wire melts due to the ___________ effect of electric current.
Answer: heating
- The SI unit of electric current is ___________.
Answer: ampere
- ___________ wire is commonly used in heating appliances due to its high resistance and high melting point.
Answer: Nichrome
Multiple Choice Questions (MCQs) and Answers:
- Which of the following is a good conductor of electricity?
- a) Rubber b) Plastic c) Copper d) Wood
Answer: c) Copper
- The device used to measure electric current is:
- a) Voltmeter b) Ammeter c) Galvanometer d) Thermometer
Answer: b) Ammeter
- What happens when current passes through a solenoid?
- a) It produces light b) It produces heat c) It behaves like a magnet d) It stores charge
Answer: c) It behaves like a magnet
- Which of these is not based on the heating effect of electric current?
- a) Electric iron b) Electric bulb c) Microwave oven d) Electric heater
Answer: c) Microwave oven
- Which material is not attracted by a magnet?
- a) Iron b) Nickel c) Cobalt d) Aluminium
Answer: d) Aluminium
True/False Questions and Answers:
- Electric current flows from lower potential to higher potential.
Answer: False - All metals are good conductors of electricity.
Answer: True - A solenoid converts electrical energy into mechanical energy.
Answer: False - A fuse protects a circuit from damage by breaking the circuit when excess current flows.
Answer: True - Overloading can lead to short circuiting in an electric circuit.
Answer: True
Short Questions and Answers:
- What is an electromagnet?
Answer: An electromagnet is a temporary magnet formed by passing electric current through a coil wound around a soft iron core.
- What do you mean by electric current?
Answer: Electric current is the flow of electric charges through a conductor per unit time.
- What are conductors and insulators?
Answer: Conductors allow electric current to pass through them, while insulators do not.
- Why is copper used in electrical wiring?
Answer: Copper is used because it is a good conductor and has low resistance.
- What causes the heating effect in an electric circuit?
Answer: The resistance of the wire causes it to heat up as electric current flows through it.
Competency Based Questions (Assertion and Reasoning):
- Assertion (A): A fuse wire is made of a material with low melting point.
Reason (R): It should melt easily when excessive current flows.
Answer: Both A and R are true, and R is the correct explanation of A.
- Assertion (A): Soft iron is preferred as the core of an electromagnet.
Reason (R): It gets magnetized and demagnetized quickly.
Answer: Both A and R are true, and R is the correct explanation of A.
- Assertion (A): An electric bulb glows when current flows through it.
Reason (R): The filament offers resistance which produces heat and light.
Answer: Both A and R are true, and R is the correct explanation of A.
- Assertion (A): Connecting many appliances to a single socket may cause a fire.
Reason (R): It can lead to overloading and overheating.
Answer: Both A and R are true, and R is the correct explanation of A.
- Assertion (A): Aluminium is a better conductor than copper.
Reason (R): It has lower resistivity than copper.
Answer: A is false but R is true.
High Order Thinking Skill (HOTS) Questions and Answers:
- Why are electric wires not made from materials like rubber or plastic?
Answer: Rubber and plastic are insulators and do not allow current to pass, hence cannot be used as conductors in electric wiring.
- A bulb and an electric heater are connected in series. Which appliance will produce more heat and why?
Answer: The heater will produce more heat as it has a wire (element) with higher resistance designed for heat production.
- Why does a fuse wire have high resistance and low melting point?
Answer: So it heats up quickly and melts when excessive current flows, thereby breaking the circuit and preventing damage.
- What happens if the core of an electromagnet is replaced by steel?
Answer: Steel remains magnetized for longer, making the electromagnet less effective for applications requiring quick magnetization and demagnetization.
- Why should we not use copper wire as a fuse wire?
Answer: Copper has a high melting point and low resistance, so it won’t melt easily during excess current flow and may not protect the circuit effectively.
Long Questions and Answers (50–60 words):
- Explain how an electric bell works.
Answer: An electric bell has an electromagnet, armature, hammer, and bell. When current flows, the electromagnet attracts the armature, causing the hammer to hit the bell. This also breaks the circuit, demagnetizing the core and allowing the armature to return. The cycle repeats, creating a ringing sound.
- What precautions should be taken while using electricity at home?
Answer: Never touch electrical appliances with wet hands. Avoid overloading sockets. Use properly rated fuses. Ensure all wires are insulated. Regularly check for loose connections. Turn off appliances when not in use. Install safety devices like circuit breakers to avoid electric shock or fire.
- Describe the construction and working of an electromagnet.
Answer: An electromagnet consists of a coil of wire wound around a soft iron core. When current passes through the coil, it produces a magnetic field, magnetizing the iron core. The strength can be increased by adding more turns or increasing current. When current stops, the core loses magnetism quickly.
- How does a fuse protect an electric circuit?
Answer: A fuse contains a thin wire of low melting point. When current exceeds the safe limit, the wire heats up and melts, breaking the circuit. This prevents overheating and damage to appliances or the risk of fire due to excess current flow.
- Why is it dangerous to connect too many appliances to one socket?
Answer: Connecting many appliances to one socket increases the total current drawn. If it exceeds the wire’s capacity, it can cause overheating, leading to melting insulation, short circuits, or even fire. This is known as overloading and is a major electrical hazard.
Additional Questions And Answers – 02
Fill in the Blanks Questions and Answers
- Question: In an electric cell, chemical energy is converted into ______ energy.
Answer: In an electric cell, chemical energy is converted into electrical - Question: The flow of electric current through a wire can produce ______ energy, as seen in a toaster.
Answer: The flow of electric current through a wire can produce heat energy, as seen in a toaster. - Question: The heating effect of electric current depends on the strength of the current, the resistance of the wire, and the ______ for which the current flows.
Answer: The heating effect of electric current depends on the strength of the current, the resistance of the wire, and the time for which the current flows. - Question: Nichrome wire is used in heating coils because it has a high ______ point and high resistivity.
Answer: Nichrome wire is used in heating coils because it has a high melting point and high resistivity. - Question: In an electric bulb, the filament becomes ______-hot and emits light when current flows through it.
Answer: In an electric bulb, the filament becomes white-hot and emits light when current flows through it. - Question: An electric fuse is a safety device used to limit the ______ in an electric circuit.
Answer: An electric fuse is a safety device used to limit the current in an electric circuit. - Question: A short circuit occurs due to the touching of the ______ and neutral wires.
Answer: A short circuit occurs due to the touching of the live and neutral wires. - Question: The magnetic effect of electric current was first observed by Hans Christian ______.
Answer: The magnetic effect of electric current was first observed by Hans Christian Oersted. - Question: A current-carrying wire can deflect a ______ needle, showing its magnetic effect.
Answer: A current-carrying wire can deflect a compass needle, showing its magnetic effect. - Question: An electromagnet is a coil of insulated wire wrapped around a ______ core that behaves like a magnet when current flows.
Answer: An electromagnet is a coil of insulated wire wrapped around a cylindrical core that behaves like a magnet when current flows. - Question: The strength of an electromagnet increases by using a ______ iron core.
Answer: The strength of an electromagnet increases by using a soft iron core. - Question: Electromagnets are used in ______ bells, loudspeakers, and cranes.
Answer: Electromagnets are used in electric bells, loudspeakers, and cranes. - Question: In an electric bell, the ______ is struck when the armature is attracted by the electromagnet.
Answer: In an electric bell, the gong is struck when the armature is attracted by the electromagnet. - Question: The filament of an electric bulb is usually made of ______ because of its high melting point.
Answer: The filament of an electric bulb is usually made of tungsten because of its high melting point. - Question: Miniature Circuit Breakers (MCBs) automatically turn off when the current exceeds the ______ limit.
Answer: Miniature Circuit Breakers (MCBs) automatically turn off when the current exceeds the safety - Question: Overloading occurs when more than one device is connected to a single ______.
Answer: Overloading occurs when more than one device is connected to a single socket. - Question: A current-carrying coil with many turns is called a ______, which acts like a bar magnet.
Answer: A current-carrying coil with many turns is called a solenoid, which acts like a bar magnet. - Question: The heating effect of electric current is used in devices like electric ______ and geysers.
Answer: The heating effect of electric current is used in devices like electric heaters and geysers. - Question: The heat produced in a wire increases with an increase in the ______ of the current.
Answer: The heat produced in a wire increases with an increase in the strength of the current. - Question: Fuse wires are often made from an alloy of tin and ______ due to its low melting point.
Answer: Fuse wires are often made from an alloy of tin and lead due to its low melting point.
Multiple Choice Questions and Answers
- Question: What type of energy is converted into electrical energy in an electric cell?
a) Mechanical energy
b) Chemical energy
c) Heat energy
d) Light energy
Answer: b) Chemical energy - Question: What effect is observed when electric current flows through the filament of a toaster?
a) Magnetic effect
b) Heating effect
c) Light effect
d) Sound effect
Answer: b) Heating effect - Question: According to Joule, the heat produced in a wire depends on:
a) The color of the wire
b) The strength of the current and resistance
c) The weight of the wire
d) The shape of the wire
Answer: b) The strength of the current and resistance - Question: Why is nichrome used in heating coils?
a) It has a low melting point
b) It has a high melting point and high resistivity
c) It is a good conductor
d) It produces light
Answer: b) It has a high melting point and high resistivity - Question: What happens to the filament of an electric bulb when current flows through it?
a) It becomes red-hot
b) It becomes white-hot and emits light
c) It cools down
d) It produces sound
Answer: b) It becomes white-hot and emits light - Question: What is the purpose of an electric fuse in a circuit?
a) To increase the current
b) To limit the current and protect appliances
c) To produce heat
d) To create magnetism
Answer: b) To limit the current and protect appliances - Question: What causes a short circuit?
a) Using a battery
b) Touching of live and neutral wires
c) Increasing the resistance
d) Using an electromagnet
Answer: b) Touching of live and neutral wires - Question: Who first established the relationship between electricity and magnetism?
a) Joule
b) Hans Christian Oersted
c) Thomas Edison
d) Michael Faraday
Answer: b) Hans Christian Oersted - Question: What does a current-carrying wire deflect in Activity 4?
a) A light bulb
b) A compass needle
c) A steel wool
d) A heating coil
Answer: b) A compass needle - Question: What is an electromagnet?
a) A permanent magnet
b) A coil of insulated wire that acts like a magnet when current flows
c) A heating coil
d) A fuse wire
Answer: b) A coil of insulated wire that acts like a magnet when current flows - Question: How can the strength of an electromagnet be increased?
a) By reducing the number of turns in the coil
b) By using a soft iron core and increasing the current
c) By using a plastic core
d) By decreasing the current
Answer: b) By using a soft iron core and increasing the current - Question: Where are electromagnets commonly used?
a) In electric bulbs
b) In electric bells and cranes
c) In electric fuses
d) In heating coils
Answer: b) In electric bells and cranes - Question: What happens in an electric bell when the current flows through the electromagnet?
a) The gong is struck
b) The circuit remains open
c) The armature moves away
d) The bell stops ringing
Answer: a) The gong is struck - Question: Why is tungsten used in electric bulb filaments?
a) It has a low melting point
b) It has a high melting point and glows brightly
c) It is a good insulator
d) It produces heat only
Answer: b) It has a high melting point and glows brightly - Question: What is the function of Miniature Circuit Breakers (MCBs)?
a) They produce heat
b) They automatically turn off when current exceeds the safety limit
c) They increase the current
d) They create magnetism
Answer: b) They automatically turn off when current exceeds the safety limit - Question: What is overloading in an electric circuit?
a) Using a single device
b) Connecting more than one device to a single socket
c) Using a fuse wire
d) Reducing the current
Answer: b) Connecting more than one device to a single socket - Question: What is a solenoid?
a) A heating coil
b) A current-carrying coil that acts like a bar magnet
c) A fuse wire
d) A light bulb
Answer: b) A current-carrying coil that acts like a bar magnet - Question: Which device uses the heating effect of electric current?
a) Electric bell
b) Electric heater
c) Electromagnet
d) Loudspeaker
Answer: b) Electric heater - Question: What happens to the heat produced in a wire when the strength of the current increases?
a) It decreases
b) It remains the same
c) It increases
d) It stops
Answer: c) It increases - Question: What material is commonly used for fuse wires due to its low melting point?
a) Nichrome
b) Tungsten
c) An alloy of tin and lead
d) Copper
Answer: c) An alloy of tin and lead
True/False Questions and Answers
- Question: In an electric cell, chemical energy is converted into electrical energy.
Answer: True - Question: The heating effect of electric current is observed when a wire becomes red-hot.
Answer: True - Question: The heat produced in a wire depends only on the strength of the current.
Answer: False (It also depends on resistance and time.) - Question: Nichrome is used in heating coils because it has a low melting point.
Answer: False (It has a high melting point.) - Question: The filament of an electric bulb becomes white-hot and emits light.
Answer: True - Question: An electric fuse increases the current in a circuit.
Answer: False (It limits the current.) - Question: A short circuit occurs due to the touching of live and neutral wires.
Answer: True - Question: Hans Christian Oersted discovered the magnetic effect of electric current.
Answer: True - Question: A current-carrying wire cannot deflect a compass needle.
Answer: False (It can deflect a compass needle.) - Question: An electromagnet loses its magnetism when the current is switched off.
Answer: True - Question: The strength of an electromagnet decreases with a soft iron core.
Answer: False (It increases with a soft iron core.) - Question: Electromagnets are used in electric bells and cranes.
Answer: True - Question: In an electric bell, the gong is struck when the circuit is broken.
Answer: False (The gong is struck when the armature is attracted.) - Question: Tungsten is used in electric bulb filaments because of its high melting point.
Answer: True - Question: Miniature Circuit Breakers (MCBs) manually turn off the circuit.
Answer: False (They automatically turn off.) - Question: Overloading occurs when multiple devices are connected to a single socket.
Answer: True - Question: A solenoid is a current-carrying coil that acts like a bar magnet.
Answer: True - Question: The heating effect of electric current is used in loudspeakers.
Answer: False (It is used in heaters and bulbs.) - Question: The heat produced in a wire decreases with an increase in current strength.
Answer: False (It increases.) - Question: Fuse wires are made from materials with a high melting point.
Answer: False (They have a low melting point.)
Short Questions and Answers
- Question: What energy is converted into electrical energy in an electric cell?
Answer: Chemical energy. - Question: What effect is observed in a toaster due to electric current?
Answer: Heating effect. - Question: Name one factor that affects the heating effect of electric current.
Answer: Strength of the current. - Question: Why is nichrome used in heating coils?
Answer: It has a high melting point and high resistivity. - Question: What happens to the filament of an electric bulb when current flows?
Answer: It becomes white-hot and emits light. - Question: What is the purpose of an electric fuse?
Answer: To limit the current and protect appliances. - Question: What causes a short circuit?
Answer: Touching of live and neutral wires. - Question: Who discovered the magnetic effect of electric current?
Answer: Hans Christian Oersted. - Question: What does a current-carrying wire deflect?
Answer: A compass needle. - Question: What is an electromagnet?
Answer: A coil of insulated wire that acts like a magnet when current flows. - Question: How can the strength of an electromagnet be increased?
Answer: By using a soft iron core. - Question: Name one device that uses an electromagnet.
Answer: Electric bell. - Question: What happens in an electric bell when the current flows?
Answer: The gong is struck. - Question: Why is tungsten used in electric bulb filaments?
Answer: It has a high melting point. - Question: What is the function of Miniature Circuit Breakers (MCBs)?
Answer: They automatically turn off when current exceeds the safety limit. - Question: What is overloading in an electric circuit?
Answer: Connecting multiple devices to a single socket. - Question: What is a solenoid?
Answer: A current-carrying coil that acts like a bar magnet. - Question: Name a device that uses the heating effect of electric current.
Answer: Electric heater. - Question: What happens to the heat in a wire when current strength increases?
Answer: It increases. - Question: What material is used for fuse wires?
Answer: An alloy of tin and lead.
Competency-Based Questions and Answers (Reasoning and Assertion)
- Question: Assertion (A): The heating effect of electric current is used in electric heaters.
Reason (R): Electric current produces heat in a wire due to its resistance.
Answer: Both A and R are true, and R is the correct explanation of A. Electric heaters work by using the heating effect of current, where the resistance of the heating coil (like nichrome) causes it to become red-hot, producing heat for practical use, as explained by Joule’s findings on the heating effect. - Question: Assertion (A): An electric fuse prevents damage to appliances in a circuit.
Reason (R): It melts and breaks the circuit when the current exceeds the safe limit.
Answer: Both A and R are true, and R is the correct explanation of A. An electric fuse protects appliances by melting when the current exceeds the safe limit due to a short circuit or overloading, breaking the circuit and stopping the current flow, thus preventing overheating and potential fires. - Question: Assertion (A): A current-carrying wire can deflect a compass needle.
Reason (R): Electric current produces a magnetic effect around the wire.
Answer: Both A and R are true, and R is the correct explanation of A. Hans Christian Oersted discovered that a current-carrying wire produces a magnetic effect, as seen in Activity 4, where the wire deflects a compass needle due to the magnetic field created, demonstrating the magnetic effect of electric current. - Question: Assertion (A): Electromagnets lose their magnetism when the current is switched off.
Reason (R): Electromagnets are made using a soft iron core that does not retain magnetism.
Answer: Both A and R are true, and R is the correct explanation of A. Electromagnets, as in Activity 6, lose magnetism when the current stops because they use a soft iron core, which does not retain magnetism, unlike steel, making them ideal for devices like electric bells that require temporary magnetism. - Question: Assertion (A): The filament of an electric bulb becomes white-hot and emits light.
Reason (R): Tungsten has a high melting point and glows brightly when heated.
Answer: Both A and R are true, and R is the correct explanation of A. The filament in an electric bulb, made of tungsten, becomes white-hot due to the heating effect of current, and because of tungsten’s high melting point and ability to glow brightly, it emits light efficiently without burning out quickly. - Question: Assertion (A): Nichrome is used in heating coils of electric heaters.
Reason (R): Nichrome has a low melting point and low resistivity.
Answer: A is true, but R is false. Nichrome is used in heating coils because it has a high melting point and high resistivity, allowing it to become red-hot without melting and to produce significant heat due to its resistance, making it ideal for devices like electric heaters and geysers. - Question: Assertion (A): An electric bell rings continuously when the switch is pressed.
Reason (R): The circuit in an electric bell is alternately made and broken rapidly.
Answer: Both A and R are true, and R is the correct explanation of A. The electric bell rings continuously because the electromagnet attracts the armature, striking the gong, then breaks the circuit, losing magnetism. The armature returns, completing the circuit again, and this rapid cycle repeats, producing continuous ringing as long as the switch is pressed. - Question: Assertion (A): Miniature Circuit Breakers (MCBs) are better than fuse wires.
Reason (R): MCBs automatically turn off the circuit without needing replacement.
Answer: Both A and R are true, and R is the correct explanation of A. MCBs are better than fuse wires because they automatically turn off the circuit when the current exceeds the safety limit, using the magnetic effect, and can be reset, unlike fuse wires that melt and need replacement after breaking the circuit. - Question: Assertion (A): The heat produced in a wire increases with the strength of the current.
Reason (R): Joule’s experiments showed that heat depends on the current, resistance, and time.
Answer: Both A and R are true, and R is the correct explanation of A. Joule’s experiments established that the heat produced in a wire increases with the strength of the current, as seen in Activity 2, where a stronger current from a battery made the nichrome wire red-hot faster, due to its dependence on current, resistance, and time. - Question: Assertion (A): A solenoid acts like a bar magnet.
Reason (R): A current-carrying coil produces magnetic effects similar to a bar magnet.
Answer: Both A and R are true, and R is the correct explanation of A. A solenoid, a coil with many turns, produces magnetic effects like a bar magnet when current flows, with one end acting as a north pole and the other as a south pole, demonstrating the magnetic effect of electric current.
High Order Thinking Skills (HOTS) Questions and Answers
- Question: Why might the heating effect of electric current be both advantageous and disadvantageous, and what does this suggest about the need for efficient energy transmission?
Answer: The heating effect is advantageous in heaters and bulbs, converting electrical energy into heat or light, but disadvantageous in transmission lines, where heat loss wastes energy and can damage insulation. This suggests efficient energy transmission is crucial, requiring low-resistance wires and proper insulation to minimize heat loss, ensuring more electrical energy reaches consumers while reducing risks like fires. - Question: How does the design of an electric fuse utilize the heating effect of current, and what does this indicate about the importance of material selection in safety devices?
Answer: An electric fuse uses the heating effect by melting when excessive current flows, breaking the circuit to prevent damage, as seen in Activity 3 with steel wool. This indicates material selection is critical—using alloys like tin and lead with low melting points ensures the fuse melts quickly, highlighting the need for precise material properties in designing effective safety devices. - Question: Why might the magnetic effect of electric current be significant in modern technology, and what does this reveal about the interplay between electricity and magnetism?
Answer: The magnetic effect is significant in devices like electromagnets in cranes, bells, and loudspeakers, enabling precise control of magnetism with current. This reveals the deep interplay between electricity and magnetism, as discovered by Oersted, where electric current generates magnetic fields, forming the basis of electromagnetism, a cornerstone of modern technology, from motors to communication devices. - Question: How does the working of an electric bell demonstrate the magnetic effect of current, and what does this suggest about the role of rapid circuit changes in device functionality?
Answer: The electric bell uses the magnetic effect as the electromagnet attracts the armature, striking the gong, then loses magnetism when the circuit breaks, repeating rapidly. This suggests rapid circuit changes are crucial for functionality in devices like bells, enabling continuous operation through alternating magnetism, highlighting the importance of dynamic electrical systems in practical applications. - Question: Why might increasing the number of turns in an electromagnet increase its strength, and what does this indicate about the relationship between current and magnetic fields?
Answer: Increasing the number of turns in an electromagnet increases its strength, as in Activity 6, because more turns amplify the magnetic field produced by the current, as each loop adds to the field. This indicates a direct relationship between current and magnetic fields, where more current loops enhance magnetism, showing how electricity can be manipulated to control magnetic effects. - Question: How does the choice of a soft iron core in electromagnets enhance their utility, and what does this reveal about the need for temporary magnetism in devices?
Answer: A soft iron core in electromagnets enhances utility by not retaining magnetism when the current stops, as in Activity 6, allowing on-off magnetic control in devices like bells and cranes. This reveals the need for temporary magnetism in devices requiring precise, switchable magnetic effects, ensuring functionality without residual magnetism interfering with operations, unlike permanent magnets. - Question: Why might the heating effect of current in transmission lines pose a challenge, and what does this suggest about the balance between energy efficiency and safety?
Answer: The heating effect in transmission lines causes energy loss as heat radiates into the atmosphere and can damage insulation, risking fires. This suggests a balance between energy efficiency and safety is needed—using low-resistance wires reduces heat loss, while proper insulation and safety devices like fuses ensure protection, optimizing energy delivery while minimizing risks in electrical systems. - Question: How does the solenoid’s behavior as a bar magnet illustrate the magnetic effect of current, and what does this indicate about the potential for creating magnetic fields without traditional magnets?
Answer: A solenoid acts like a bar magnet, with one end as a north pole and the other as a south pole, due to the magnetic field created by current in its coil, as noted in the text. This indicates electric current can create magnetic fields without traditional magnets, offering a controllable, temporary magnetism vital for applications like electromagnets in modern technology. - Question: Why might the use of tungsten in electric bulbs be critical for their functionality, and what does this reveal about the role of material properties in electrical devices?
Answer: Tungsten’s high melting point and ability to glow brightly when white-hot, as in electric bulbs, ensure it can withstand high temperatures and emit light efficiently without burning out. This reveals material properties are crucial in electrical devices, as selecting materials like tungsten with specific traits ensures functionality, durability, and efficiency, tailoring devices to their intended energy transformations. - Question: How does the rapid making and breaking of the circuit in an electric bell ensure continuous ringing, and what does this suggest about the integration of electrical and mechanical components?
Answer: The electric bell’s rapid circuit making and breaking—where the electromagnet attracts the armature, breaks the circuit, and repeats—ensures continuous ringing by striking the gong repeatedly. This suggests integrating electrical (electromagnet) and mechanical (armature, gong) components allows dynamic functionality, as electrical signals drive mechanical actions, highlighting the synergy needed for effective operation in electromechanical devices.
Long Questions and Answers (50-60 Words)
- Question: Describe the heating effect of electric current and its factors.
Answer: The heating effect of electric current occurs when current flows through a wire, producing heat, as in a toaster. Joule found that heat depends on the current’s strength, the wire’s resistance, and the time of flow. In Activity 2, a nichrome wire became red-hot, showing increased heat with higher current, demonstrating these factors’ role in heat production. - Question: Explain how an electric fuse protects a circuit from damage.
Answer: An electric fuse protects a circuit by melting when the current exceeds the safe limit, as in short circuits or overloading, breaking the circuit. This stops the current flow, preventing overheating and fires, as seen in Activity 3 with steel wool. Fuses, made of tin-lead alloys, ensure appliances are safeguarded by interrupting excessive current flow. - Question: Discuss the magnetic effect of electric current observed in Activity 4.
Answer: In Activity 4, a current-carrying wire deflected a compass needle, demonstrating the magnetic effect of electric current. Discovered by Oersted, this shows that current produces a magnetic field, acting like a magnet. The deflection lasts while the current flows, indicating electricity can create magnetism, a principle used in devices like electromagnets and electric bells. - Question: Describe how an electromagnet works and how its strength can be increased.
Answer: An electromagnet works when current flows through a coil wrapped around a core, creating a magnetic field, as in Activity 6. Its strength increases by using a soft iron core, adding more turns to the coil, or increasing the current. This temporary magnetism, lost when current stops, makes electromagnets useful in devices like bells and cranes. - Question: Explain the working of an electric bell using the magnetic effect.
Answer: An electric bell works using the magnetic effect—current flows through the electromagnet, attracting the armature, striking the gong. The circuit breaks, the electromagnet loses magnetism, and the armature returns, completing the circuit again. This rapid cycle repeats, making the bell ring continuously while the switch is pressed, demonstrating the interplay of electricity and magnetism. - Question: Discuss the advantages and disadvantages of the heating effect of current.
Answer: The heating effect of current is advantageous in heaters and bulbs, producing heat and light, but disadvantageous in transmission lines, where heat loss wastes energy and can damage insulation. Devices like electric irons benefit, while energy loss in wires highlights the need for efficient transmission methods to reduce waste and ensure safety in electrical systems. - Question: Describe how the filament of an electric bulb produces light.
Answer: The filament of an electric bulb, made of tungsten, becomes white-hot when current flows due to the heating effect. Tungsten’s high melting point allows it to withstand high temperatures, glowing brightly and emitting light. This energy conversion from electrical to light energy makes bulbs effective, with tungsten ensuring durability and brightness during operation. - Question: Explain the role of Miniature Circuit Breakers (MCBs) in safety.
Answer: Miniature Circuit Breakers (MCBs) enhance safety by automatically turning off the circuit when the current exceeds the safety limit, often using the magnetic effect. Unlike fuses, MCBs don’t need replacement, as they can be reset, preventing damage from short circuits or overloading, ensuring appliances are protected efficiently in household circuits. - Question: Discuss the practical uses of electromagnets in daily life.
Answer: Electromagnets are used in electric bells, where they enable ringing, in cranes to lift heavy iron objects, and in loudspeakers for sound production. They also help doctors remove magnetic materials from eyes and are found in toys. Their temporary magnetism, controlled by current, makes them versatile for applications requiring switchable magnetic effects in daily life. - Question: Explain how a solenoid mimics a bar magnet.
Answer: A solenoid mimics a bar magnet as current flows through its coil, creating a magnetic field with one end as a north pole and the other as a south pole. This magnetic effect, similar to a bar magnet, arises from the current, making solenoids useful in applications like electromagnets, where controlled magnetism is needed.