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Electricity: Magnetic & Heating Effects Class 8 Worksheet PDF
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Ch 4: Electricity: Magnetic and Heating Effects NCERT book: Curiosity
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Electricity: Magnetic & Heating EffectsClass 8 Science (Curiosity) · Chapter 4 · Worksheet with full solutions
64questions
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88minutes
24MCQs
Tap an option to check it instantly, then tap Check answer for the reason. Short and long answers carry the full explanation, not just the final line.
1What happens when electric current passes through a nichrome wire? [1]
(a) It gets warm(b) It remains cool(c) It glows brightly(d) It turns into copper wire
Check answer
(a) It gets warm
Nichrome has high resistance. When current flows, that resistance converts part of the electrical energy into heat, so the wire warms up. This is the heating effect of electric current.
Nichrome has high resistance. When current flows, that resistance converts part of the electrical energy into heat, so the wire warms up. This is the heating effect of electric current.
2Which component in a dry cell serves as the positive terminal? [1]
(a) Aluminium cap(b) Paste-like electrolyte(c) Zinc container(d) Carbon rod
Check answer
(d) Carbon rod
In a dry cell the carbon rod, with its metallic cap on top, is the positive terminal. The zinc container is the negative terminal.
In a dry cell the carbon rod, with its metallic cap on top, is the positive terminal. The zinc container is the negative terminal.
3What is the main reason countries are focusing on battery recycling and development? [1]
(a) To prevent chemical leaks from used batteries(b) To reduce battery sizes(c) To boost sales of electric vehicles(d) To ensure sustainable use of limited resources like lithium and cobalt
Check answer
(d) To ensure sustainable use of limited resources (lithium and cobalt)
Lithium and cobalt occur in limited quantities on earth. Recycling lets the same metals be used again instead of mining more, which is why it is a global priority.
Lithium and cobalt occur in limited quantities on earth. Recycling lets the same metals be used again instead of mining more, which is why it is a global priority.
4Which household device does NOT work on the heating effect of electric current? [1]
(a) Electric stove(b) Electric room heater(c) Electric fan(d) Hair dryer
Check answer
(c) Electric fan
A fan runs on an electric motor, which uses the magnetic effect of current. The stove, room heater and hair dryer all contain heating elements.
A fan runs on an electric motor, which uses the magnetic effect of current. The stove, room heater and hair dryer all contain heating elements.
5What is the role of the electrolyte in a battery? [1]
(a) To act as the battery's positive terminal(b) To trigger chemical reactions for electricity generation(c) To neutralise the battery's metal plates(d) To support the battery's physical framework
Check answer
(b) To trigger chemical reactions for electricity generation
The electrolyte lets ions move between the electrodes. That movement is what keeps the chemical reaction going, and the reaction is what produces the current.
The electrolyte lets ions move between the electrodes. That movement is what keeps the chemical reaction going, and the reaction is what produces the current.
6Heat produced in a heating element on passing current through it depends on:
(i) nature of the material (ii) thickness of the wire (iii) colour of the element (iv) length of the wire [1]
(a) (i) and (ii) only(b) (i), (ii) and (iv) only(c) (i), (ii), (iii) and (iv)(d) (ii) and (iii) only
Check answer
(b) (i), (ii) and (iv) only
Heat depends on resistance, and resistance depends on the material, the thickness and the length of the wire. Colour has nothing to do with resistance, so (iii) is wrong.
Heat depends on resistance, and resistance depends on the material, the thickness and the length of the wire. Colour has nothing to do with resistance, so (iii) is wrong.
7What change will a compass needle show if an electromagnet is turned on and off repeatedly? [1]
(a) Moves in random directions(b) Spins continuously(c) Deflects and returns to its original position(d) Stops working eventually
Check answer
(c) Deflects and returns to its original position
The magnetic field exists only while current flows. So the needle deflects when the electromagnet is switched on and swings back when it is switched off.
The magnetic field exists only while current flows. So the needle deflects when the electromagnet is switched on and swings back when it is switched off.
8What happens to the compass needle when current flows through a nearby wire? [1]
(a) It deflects(b) It points to South(c) It points to North(d) It stays still
Check answer
(a) It deflects
The current creates a magnetic field around the wire. The needle, being a small magnet, turns away from its usual north-south position. This is exactly what Oersted observed.
The current creates a magnetic field around the wire. The needle, being a small magnet, turns away from its usual north-south position. This is exactly what Oersted observed.
9How does increasing the number of coil turns affect an electromagnet? [1]
(a) Decreases its strength(b) Increases its strength(c) Reduces the flow of electricity(d) Makes it stop working
Check answer
(b) Increases its strength
Each turn of the coil adds to the magnetic field, so more turns make a stronger electromagnet. Increasing the current does the same.
Each turn of the coil adds to the magnetic field, so more turns make a stronger electromagnet. Increasing the current does the same.
10What causes a wire to get heated when current passes through it? [1]
(a) Hot temperature in the room(b) Shiny surface of the wire(c) The flow of cool breeze(d) Resistance of the wire
Check answer
(d) Resistance of the wire
Resistance opposes the flow of charge, and that opposition converts electrical energy into heat energy inside the wire.
Resistance opposes the flow of charge, and that opposition converts electrical energy into heat energy inside the wire.
11The magnetic effect of electric current generates a magnetic field around a current-carrying coil [1]
(a) When the electric current is flowing through the coil(b) When the coil becomes hot(c) When the current stops flowing(d) When the coil is brought near another magnet
Check answer
(a) When the electric current is flowing through the coil
No current means no magnetic field. The field appears the moment current starts and disappears the moment it stops.
No current means no magnetic field. The field appears the moment current starts and disappears the moment it stops.
12In a dry cell the positive terminal is the metallic tip on top of the carbon rod. Which then is the negative terminal? [1]
(a) Bottom of the zinc container(b) Carbon rod just below the metallic tip(c) The paste of chemicals inside the cell(d) Bottom of the carbon rod
Check answer
(a) Bottom of the zinc container
The whole zinc container acts as the negative terminal, and its base is the point we connect to in a torch or a clock.
The whole zinc container acts as the negative terminal, and its base is the point we connect to in a torch or a clock.
13What is the difference between Voltaic cells and dry cells? [1]
(a) Both use liquid electrolytes(b) They are identical in structure and function(c) Voltaic cells use a solid electrolyte; dry cells use a liquid one(d) Voltaic cells use a liquid electrolyte; dry cells use a paste
Check answer
(d) Voltaic cells use a liquid electrolyte; dry cells use a paste
Because the dry cell uses a thick moist paste instead of a liquid, it does not spill and can be carried around, which is why torches and remotes use it.
Because the dry cell uses a thick moist paste instead of a liquid, it does not spill and can be carried around, which is why torches and remotes use it.
14Who discovered the link between electricity and magnetism? [1]
(a) Albert Einstein(b) Hans Christian Oersted(c) Isaac Newton(d) Thomas Edison
Check answer
(b) Hans Christian Oersted
In 1820 Oersted noticed a compass needle move when current flowed through a nearby wire, and that observation started the whole subject of electromagnetism.
In 1820 Oersted noticed a compass needle move when current flowed through a nearby wire, and that observation started the whole subject of electromagnetism.
15Why does a wire carrying electric current act like a magnet? [1]
(a) It changes its shape into a magnet(b) It conducts electricity efficiently(c) It creates a magnetic field like a magnet does(d) It heats up and attracts metals
Check answer
(c) It creates a magnetic field like a magnet does
A moving charge always produces a magnetic field around it, so the wire behaves like a magnet while the current is on.
A moving charge always produces a magnetic field around it, so the wire behaves like a magnet while the current is on.
16What is a common use of rechargeable batteries? [1]
(a) Used in non-electronic products(b) Used multiple times after charging(c) Used only in medical equipment(d) Used once and then disposed of
Check answer
(b) Used multiple times after charging
The chemical reaction inside them can be reversed by charging, so the same battery works again and again. Phones, laptops and electric vehicles all use them.
The chemical reaction inside them can be reversed by charging, so the same battery works again and again. Phones, laptops and electric vehicles all use them.
17What type of compass needle movement is observed when electric current is stopped? [1]
(a) It starts vibrating(b) It returns to its original direction(c) It spins continuously(d) It keeps deflecting
Check answer
(b) It returns to its original direction
With no current there is no magnetic field from the wire, so the needle settles back along the earth's north-south direction.
With no current there is no magnetic field from the wire, so the needle settles back along the earth's north-south direction.
18In which part of the cell does the chemical reaction occur to produce electricity? [1]
(a) Within the LED terminal(b) Between the electrodes only(c) Inside the metal plates(d) In the electrolyte
Check answer
(d) In the electrolyte
The reaction takes place between the electrodes and the electrolyte, and it is the electrolyte that allows the ions to move and the reaction to continue.
The reaction takes place between the electrodes and the electrolyte, and it is the electrolyte that allows the ions to move and the reaction to continue.
19What is produced around a current-carrying conductor? [1]
(a) Electric field(b) Magnetic field(c) No field is produced(d) Gravitational field
Check answer
(b) Magnetic field
This is the magnetic effect of electric current, and it is the basis of electromagnets, electric bells and motors.
This is the magnetic effect of electric current, and it is the basis of electromagnets, electric bells and motors.
20Wires made of which material are most suitable for showing the heating effect of electric current? [1]
(a) Copper wire(b) Aluminium(c) Nichrome(d) Silver
Check answer
(c) Nichrome
Nichrome has high resistance and a high melting point, so it produces a lot of heat without melting. Copper and silver have low resistance and are used for carrying current, not for heating.
Nichrome has high resistance and a high melting point, so it produces a lot of heat without melting. Copper and silver have low resistance and are used for carrying current, not for heating.
21Assertion–Reason
Assertion (A): Connecting multiple cells results in a stronger magnetic field around a coil.
Reason (R): More cells generate a greater current, which enhances the electromagnet's strength. [1]
(a) Both true, R explains A(b) Both true, R does not explain A(c) A true, R false(d) A false, R true
Check answer
(a) Both true, and R is the correct explanation of A
More cells push a larger current through the coil, and a larger current means a stronger magnetic field. So R explains exactly why A happens.
More cells push a larger current through the coil, and a larger current means a stronger magnetic field. So R explains exactly why A happens.
22Assertion–Reason
Assertion (A): Dry cells are more convenient than Voltaic cells for portable use.
Reason (R): Dry cells use a thick moist paste, avoiding spillage associated with liquid electrolytes. [1]
(a) Both true, R explains A(b) Both true, R does not explain A(c) A true, R false(d) A false, R true
Check answer
(a) Both true, and R is the correct explanation of A
A sealed paste cannot spill, so the cell can be carried in a pocket, a torch or a toy. That is precisely the reason for the convenience stated in A.
A sealed paste cannot spill, so the cell can be carried in a pocket, a torch or a toy. That is precisely the reason for the convenience stated in A.
23Assertion–Reason
Assertion (A): A current-carrying wire creates a magnetic effect similar to a permanent magnet.
Reason (R): The magnetic effect is a result of the flow of electricity through the wire. [1]
(a) Both true, R explains A(b) Both true, R does not explain A(c) A true, R false(d) A false, R true
Check answer
(a) Both true, and R is the correct explanation of A
The flow of current is what produces the field, so R gives the cause behind the behaviour described in A.
The flow of current is what produces the field, so R gives the cause behind the behaviour described in A.
24Assertion–Reason
Assertion (A): Electromagnets do not have poles like the North and South poles of a bar magnet.
Reason (R): When we interchange the battery terminals, the poles of the electromagnet also change positions. [1]
(a) Both true, R explains A(b) Both true, R does not explain A(c) A true, R false(d) A false, R true
Check answer
(d) A is false but R is true
A is wrong: an electromagnet does have a north and a south pole whenever current flows. R is correct: reversing the battery reverses the current, which swaps the two poles.
A is wrong: an electromagnet does have a north and a south pole whenever current flows. R is correct: reversing the battery reverses the current, which swaps the two poles.
25List two metals commonly used as electrodes in a Voltaic cell. [1]
Check answer
Copper and zinc.
Two different metals are needed, because the difference in how they react with the electrolyte is what creates the current.
Two different metals are needed, because the difference in how they react with the electrolyte is what creates the current.
26Explain why solid-state batteries are a significant development in battery technology. [1]
Check answer
Solid-state batteries replace the liquid or paste electrolyte with a solid material. This makes them safer (nothing to leak or catch fire), lets them charge faster, and gives them a longer life.
27Identify the scientist who discovered the link between electricity and magnetism in 1820. [1]
Check answer
Hans Christian Oersted.
28What happens to the electric current in a conductor when resistance is present? [1]
Check answer
Resistance opposes the flow of current, and some of the electrical energy is converted into heat energy inside the conductor.
29Explain the conversion process that occurs when electric current flows through a nichrome wire. [1]
Check answer
The current meets resistance in the nichrome wire, and that resistance converts electrical energy into heat energy, so the wire warms up.
30What is the observed effect when a nichrome wire is connected to a current source? [1]
Check answer
The wire becomes warm. This happens because of the heating effect caused by its electrical resistance.
31Describe how the strength of an electromagnet can be increased. [1]
Check answer
By increasing the current through the coil (using more cells), or by increasing the number of turns in the coil. Adding a soft iron core also makes it much stronger.
32Illustrate how different metal pairings affect the efficiency of a Voltaic cell. [1]
Check answer
Different pairs such as copper and zinc, or aluminium and silver, produce different voltages. Testing several pairings under the same conditions shows which combination gives the most current.
33Describe the role of the nichrome wire's properties in the heating effect of electric current. [1]
Check answer
Nichrome has high electrical resistance, which converts current into heat efficiently, and it also tolerates high temperatures without melting. Both properties make it suitable for heating elements.
34What happens to the magnetic field when an electric current stops flowing through a conductor? [1]
Check answer
The magnetic field disappears immediately. It exists only while current is flowing.
35Match the items in Column A with those in Column B. [2]
| Column A | Column B |
|---|---|
| (i) Voltaic cell | (a) Best suited for electric heater |
| (ii) Electric iron | (b) Works on magnetic effect of electric current |
| (iii) Nichrome wire | (c) Works on heating effect of electric current |
| (iv) Electromagnet | (d) Generates electricity by chemical reactions |
Check answer
| Column A | Correct match |
|---|---|
| (i) Voltaic cell | (d) Generates electricity by chemical reactions |
| (ii) Electric iron | (c) Works on heating effect of electric current |
| (iii) Nichrome wire | (a) Best suited for electric heater |
| (iv) Electromagnet | (b) Works on magnetic effect of electric current |
36Explain why a Voltaic cell eventually becomes 'dead' and stops supplying electricity. [2]
Check answer
A Voltaic cell works on a chemical reaction between the electrodes and the electrolyte. Over time the chemicals are used up. Once the reaction stops, no current can be produced and the cell is said to be dead.
37What is meant by the 'magnetic effect of electric current'? [2]
Check answer
It is the phenomenon in which an electric current flowing through a conductor produces a magnetic field around it. This field can deflect a magnetic compass or attract magnetic materials like iron.
38What creative solution is suggested for preventing energy loss and overheating in electrical circuits? [2]
Check answer
Using wires, plugs and sockets of the correct rating for the current they will carry. Components that can handle the load do not build up excessive resistance and heat.
39List the changes you would observe in the behaviour of a compass needle when varying the current through a wire. [2]
Check answer
If the current increases, the deflection of the needle becomes greater because the magnetic field is stronger. If the current decreases, the deflection reduces. Switching the current on and off makes the needle deflect and return alternately.
40How does the model of an electromagnet illustrate the magnetic effect of electric current? [2]
Check answer
An iron nail is wrapped with wire connected to a battery. When current flows, the nail attracts iron clips and behaves like a magnet. This shows that the current has created a magnetic field around the wire.
41Describe the principle that causes household appliances to generate heat when powered by electric current. [2]
Check answer
Current passing through a heating element meets resistance, and that resistance converts electrical energy into heat. The element becomes hot enough to heat, cook or dry.
42Who discovered the relationship between electricity and magnetism, and when? [2]
Check answer
Hans Christian Oersted, in 1820. He found that a current-carrying wire changes the direction of a nearby compass needle because of the magnetic field it creates.
43In a simple lemon battery setup, what happens if the LED remains unlit, and what should be done? [2]
Check answer
The most likely cause is wrong polarity. Reverse the LED connections so that its longer wire goes to the copper (positive terminal) and the shorter wire to the iron nail (negative terminal).
44Describe an application of electromagnets and how it benefits from the magnetic effect of electric current. [2]
Check answer
Lifting electromagnets in scrapyards pick up heavy metal objects. Switching the current on creates a strong field that holds the metal, and switching it off releases the load instantly, which gives complete control over lifting.
45Explain how a magnetic compass helps to demonstrate the magnetic effect of electric current. [2]
Check answer
Placed near a current-carrying conductor, the compass needle deflects from its usual direction. That deflection is direct evidence that a magnetic field has been produced around the conductor by the flow of current.
46State whether each statement is True or False. [3]
(a) The strength of an electromagnet depends on the resistance offered by the coil material.
(b) A hair dryer is an example of the magnetic effect of electric current.
(c) Safety devices are necessary in household circuits to prevent energy transmission losses due to overheating.
(b) A hair dryer is an example of the magnetic effect of electric current.
(c) Safety devices are necessary in household circuits to prevent energy transmission losses due to overheating.
Check answer
(a) False. The strength of an electromagnet depends on the number of turns, the current, and the presence of a soft iron core — not directly on the resistance of the coil material.
(b) False. A hair dryer works mainly on the heating effect: current heats a coil and a fan blows air over it.
(c) False. Safety devices prevent overheating and damage, not energy transmission losses.
(b) False. A hair dryer works mainly on the heating effect: current heats a coil and a fan blows air over it.
(c) False. Safety devices prevent overheating and damage, not energy transmission losses.
47How does the heating effect of electric current vary when a nichrome wire is connected to one cell compared to two cells? [3]
Check answer
With two cells the current through the wire is larger, so more electrical energy is converted into heat and the wire becomes hotter.
By Joule's law the heat produced is proportional to the square of the current, so doubling the current increases the heat several times over. This is why appliances that need strong heat are designed to draw a larger current.
By Joule's law the heat produced is proportional to the square of the current, so doubling the current increases the heat several times over. This is why appliances that need strong heat are designed to draw a larger current.
48What is the main difference between Voltaic cells and dry cells? [3]
Check answer
The difference is the form of the electrolyte.
Voltaic cell: the electrolyte is a liquid, usually a weak acid or a salt solution.
Dry cell: the electrolyte is a thick moist paste.
Because the paste cannot spill, dry cells are safe to carry and are used in torches, clocks and remotes. Dry cells are also usually single-use, unlike rechargeable types.
Voltaic cell: the electrolyte is a liquid, usually a weak acid or a salt solution.
Dry cell: the electrolyte is a thick moist paste.
Because the paste cannot spill, dry cells are safe to carry and are used in torches, clocks and remotes. Dry cells are also usually single-use, unlike rechargeable types.
49Identify two practical applications of electromagnets in everyday life. [3]
Check answer
1. Electric bells. An electromagnet pulls a hammer that strikes the gong, producing sound.
2. Cranes in scrapyards. A powerful electromagnet lifts heavy scrap iron and drops it exactly where needed simply by switching the current off.
2. Cranes in scrapyards. A powerful electromagnet lifts heavy scrap iron and drops it exactly where needed simply by switching the current off.
50Describe an electromagnet and explain how its magnetic strength can be altered. [3]
Check answer
An electromagnet is a coil of wire through which current flows, creating a magnetic field. Its strength can be changed in three ways:
1. Varying the current — more current gives a stronger magnet.
2. Changing the number of turns — more turns give a stronger field.
3. Inserting an iron core — a soft iron core inside the coil boosts the strength significantly.
1. Varying the current — more current gives a stronger magnet.
2. Changing the number of turns — more turns give a stronger field.
3. Inserting an iron core — a soft iron core inside the coil boosts the strength significantly.
51Evaluate the advantages of electromagnets over permanent magnets in industrial applications. [3]
Check answer
An electromagnet's strength can be adjusted by changing the current or the number of turns, which a permanent magnet cannot do.
It can also be switched on and off, so material can be picked up and released at will — exactly what a scrapyard crane needs.
This control and adaptability make electromagnets the preferred choice in industry, improving both safety and productivity.
It can also be switched on and off, so material can be picked up and released at will — exactly what a scrapyard crane needs.
This control and adaptability make electromagnets the preferred choice in industry, improving both safety and productivity.
52Design an experiment to test alternate methods of generating electricity using everyday materials. [3]
Check answer
Make a potato battery. Take several potatoes, copper coins, galvanised nails and connecting wires.
Push one coin and one nail into each potato, keeping them apart. Connect the cells in series by joining the coin of one potato to the nail of the next.
Attach a small digital clock or an LED across the free ends and observe whether it works. The experiment shows how electrochemical reactions can generate electricity from ordinary materials.
Push one coin and one nail into each potato, keeping them apart. Connect the cells in series by joining the coin of one potato to the nail of the next.
Attach a small digital clock or an LED across the free ends and observe whether it works. The experiment shows how electrochemical reactions can generate electricity from ordinary materials.
53How would you demonstrate the functionality of a battery using lemons and an LED? [3]
Check answer
Take five or six lemons, copper wires, iron nails, an LED and connecting wires.
Insert one copper wire and one iron nail into each lemon so that each lemon becomes a cell. Connect the cells in series by joining the copper of one lemon to the nail of the next.
Attach the LED between the copper of the first lemon and the nail of the last. If it does not glow, reverse its connections. A glowing LED confirms a complete circuit and shows how a battery works.
Insert one copper wire and one iron nail into each lemon so that each lemon becomes a cell. Connect the cells in series by joining the copper of one lemon to the nail of the next.
Attach the LED between the copper of the first lemon and the nail of the last. If it does not glow, reverse its connections. A glowing LED confirms a complete circuit and shows how a battery works.
54Explain how a Voltaic cell generates electricity. [3]
Check answer
Two plates of different metals, called electrodes, are partly dipped in an electrolyte such as a weak acid or salt solution.
When the circuit is closed, a chemical reaction takes place between the electrodes and the electrolyte, producing an electric current that flows through the circuit.
Over time the chemicals are consumed, the reaction stops, and the cell goes dead.
When the circuit is closed, a chemical reaction takes place between the electrodes and the electrolyte, producing an electric current that flows through the circuit.
Over time the chemicals are consumed, the reaction stops, and the cell goes dead.
55Explain why nichrome wire is used as a heating element in electrical appliances. [3]
Check answer
Nichrome has high electrical resistance, so it converts electrical energy into heat very effectively.
It also withstands high temperatures without oxidising or degrading, which keeps appliances like toasters and irons safe and durable.
Because it handles thermal stress without melting, it is ideal for both household and industrial heating.
It also withstands high temperatures without oxidising or degrading, which keeps appliances like toasters and irons safe and durable.
Because it handles thermal stress without melting, it is ideal for both household and industrial heating.
56Discuss the importance of selecting appropriate materials for household wiring. [3]
Check answer
Wires should be made of low-resistance conductors such as copper, which carry current with very little heat.
Wires must also be of the right gauge for the expected load, otherwise they overheat, waste energy and may cause fire.
Insulation that can withstand heat, along with compliance with electrical codes, completes a safe and efficient wiring system.
Wires must also be of the right gauge for the expected load, otherwise they overheat, waste energy and may cause fire.
Insulation that can withstand heat, along with compliance with electrical codes, completes a safe and efficient wiring system.
57Read the passage and answer the questions that follow. [4]
A battery generates electricity through chemical reactions between electrodes and electrolytes. The earliest type, the Voltaic cell, used two different metals and a liquid electrolyte. Later, dry cells became popular, using a zinc container and carbon rod with a paste-like electrolyte. Modern rechargeable batteries, like lithium-ion, can be reused many times. Future solid-state batteries may be safer, charge faster and last longer.
(a) Which part of a dry cell acts as the positive terminal? (1)
(b) What is the main difference between a dry cell and a Voltaic cell? (1)
(c) Why are rechargeable batteries preferred over dry cells? (2)
OR Explain why lithium-ion batteries are important for the future. (2)
(a) Which part of a dry cell acts as the positive terminal? (1)
(b) What is the main difference between a dry cell and a Voltaic cell? (1)
(c) Why are rechargeable batteries preferred over dry cells? (2)
OR Explain why lithium-ion batteries are important for the future. (2)
Check answer
(a) The carbon rod acts as the positive terminal of a dry cell.
(b) A Voltaic cell uses a liquid electrolyte, while a dry cell uses a paste-like electrolyte. The paste makes the dry cell portable and spill-proof, which is why torches and clocks use it.
(c) Rechargeable batteries can be reused many times, reducing waste and saving money. They power phones, laptops and electric vehicles. Though they eventually wear out, their repeated use makes them more economical and eco-friendly than single-use dry cells.
OR
Lithium-ion batteries are lightweight, efficient and rechargeable, and power most modern devices. As the world shifts to clean energy they play a crucial role, and solid-state versions now being developed promise to be safer, faster-charging and longer-lasting.
(b) A Voltaic cell uses a liquid electrolyte, while a dry cell uses a paste-like electrolyte. The paste makes the dry cell portable and spill-proof, which is why torches and clocks use it.
(c) Rechargeable batteries can be reused many times, reducing waste and saving money. They power phones, laptops and electric vehicles. Though they eventually wear out, their repeated use makes them more economical and eco-friendly than single-use dry cells.
OR
Lithium-ion batteries are lightweight, efficient and rechargeable, and power most modern devices. As the world shifts to clean energy they play a crucial role, and solid-state versions now being developed promise to be safer, faster-charging and longer-lasting.
58Read the passage and answer the questions that follow. [4]
When an electric current passes through a straight conductor, it produces a magnetic field around it. The direction of this field can be found using the Right-Hand Thumb Rule: if you hold the conductor in your right hand with the thumb pointing in the direction of the current, the curl of the fingers gives the direction of the magnetic field.
(a) How do you find the direction of the magnetic field around a straight conductor? (1)
(b) What does the Right-Hand Thumb Rule state? (1)
(c) How can you demonstrate the direction of the field using this rule? (2)
OR Why is the Right-Hand Thumb Rule important in electromagnetism? (2)
(a) How do you find the direction of the magnetic field around a straight conductor? (1)
(b) What does the Right-Hand Thumb Rule state? (1)
(c) How can you demonstrate the direction of the field using this rule? (2)
OR Why is the Right-Hand Thumb Rule important in electromagnetism? (2)
Check answer
(a) By using the Right-Hand Thumb Rule. Point the right thumb along the direction of the current, and the curled fingers show the direction of the magnetic field.
(b) The rule states that if a straight current-carrying conductor is held in the right hand with the thumb pointing along the current, then the curled fingers give the direction of the magnetic field.
(c) Hold the conductor in the right hand with the thumb along the current flow. The curling of the fingers around the conductor shows the direction of the field lines, making it easy to picture the circular magnetic field around the wire.
OR
The rule matters because it lets us predict the orientation of magnetic fields produced by currents. That prediction is essential for designing motors, generators and electromagnets, where current and magnetic field work together to produce motion or energy.
(b) The rule states that if a straight current-carrying conductor is held in the right hand with the thumb pointing along the current, then the curled fingers give the direction of the magnetic field.
(c) Hold the conductor in the right hand with the thumb along the current flow. The curling of the fingers around the conductor shows the direction of the field lines, making it easy to picture the circular magnetic field around the wire.
OR
The rule matters because it lets us predict the orientation of magnetic fields produced by currents. That prediction is essential for designing motors, generators and electromagnets, where current and magnetic field work together to produce motion or energy.
59Read the passage and answer the questions that follow. [4]
An electromagnet is formed when a coil of wire is wound around a material like soft iron and current is passed through it. The coil produces a magnetic field and the soft iron core becomes strongly magnetised. The magnetism remains as long as the current flows but disappears once it is switched off. Electromagnets are used in electric bells, cranes for lifting scrap iron, and electric motors.
(a) What happens to the magnetism when the current is switched off? (1)
(b) Why does soft iron make a good core? (1)
(c) How does an electromagnet in a crane help lift heavy scrap iron? (2)
OR Differentiate between a permanent magnet and an electromagnet. (2)
(a) What happens to the magnetism when the current is switched off? (1)
(b) Why does soft iron make a good core? (1)
(c) How does an electromagnet in a crane help lift heavy scrap iron? (2)
OR Differentiate between a permanent magnet and an electromagnet. (2)
Check answer
(a) The magnetism disappears, because an electromagnet works only while electric current flows through it.
(b) Soft iron becomes magnetised quickly when current flows and loses its magnetism as soon as the current is switched off, which is exactly what a temporary magnet needs.
(c) In a crane, a large coil with a soft iron core becomes a powerful electromagnet when current flows, attracting and lifting heavy scrap iron. Switching the current off releases the scrap immediately, making the process quick and controlled.
OR
A permanent magnet keeps its magnetism and cannot be switched on or off. An electromagnet works only while current flows, and its strength can be varied by changing the current, which makes it far more versatile.
(b) Soft iron becomes magnetised quickly when current flows and loses its magnetism as soon as the current is switched off, which is exactly what a temporary magnet needs.
(c) In a crane, a large coil with a soft iron core becomes a powerful electromagnet when current flows, attracting and lifting heavy scrap iron. Switching the current off releases the scrap immediately, making the process quick and controlled.
OR
A permanent magnet keeps its magnetism and cannot be switched on or off. An electromagnet works only while current flows, and its strength can be varied by changing the current, which makes it far more versatile.
60Discuss how the heating effect of electric current is used in everyday household appliances, with examples. [5]
Check answer
Many household appliances rely on the heating effect: electric room heaters, stoves, irons, kettles and hair dryers.
Each contains a heating element, usually a coil or rod made of a high-resistance material such as nichrome, which converts electrical energy into heat when connected to a power source.
In an electric iron the element gets hot and transfers heat to the baseplate, which smooths out wrinkles in fabric. In an electric kettle the element heats water to boiling point. In a hair dryer the element heats the air while a fan blows it out.
The heating effect is therefore essential for warmth, cooking and many other daily tasks.
Each contains a heating element, usually a coil or rod made of a high-resistance material such as nichrome, which converts electrical energy into heat when connected to a power source.
In an electric iron the element gets hot and transfers heat to the baseplate, which smooths out wrinkles in fabric. In an electric kettle the element heats water to boiling point. In a hair dryer the element heats the air while a fan blows it out.
The heating effect is therefore essential for warmth, cooking and many other daily tasks.
61Evaluate how lithium-ion batteries have influenced modern electronics and what challenges remain. [5]
Check answer
Lithium-ion batteries gave electronics lightweight, rechargeable and efficient power. Their high energy density made compact but powerful devices possible — smartphones, laptops and electric vehicles all depend on them.
Challenges remain. Lithium and cobalt exist in limited quantities, so supply is a concern. Overheating creates safety risks. Recycling processes are still not efficient enough for the volumes now in use.
Future work is moving towards solid-state batteries, which could offer better safety, longer life and higher performance while reducing environmental harm.
Challenges remain. Lithium and cobalt exist in limited quantities, so supply is a concern. Overheating creates safety risks. Recycling processes are still not efficient enough for the volumes now in use.
Future work is moving towards solid-state batteries, which could offer better safety, longer life and higher performance while reducing environmental harm.
62What is the magnetic effect of an electric current, and how does it relate to electromagnets? [5]
Check answer
The magnetic effect of electric current is the production of a magnetic field around a conductor whenever current flows through it.
An electromagnet puts this effect to use. A coil of wire is wound around an iron core. When current flows, the coil's magnetic field magnetises the core, turning it into a temporary but powerful magnet.
Its strength depends on the amount of current and the number of turns in the coil. Unlike a permanent magnet, it can be switched on and off, which makes it useful for lifting heavy metal in scrapyards and factories, and for electric bells and motors.
An electromagnet puts this effect to use. A coil of wire is wound around an iron core. When current flows, the coil's magnetic field magnetises the core, turning it into a temporary but powerful magnet.
Its strength depends on the amount of current and the number of turns in the coil. Unlike a permanent magnet, it can be switched on and off, which makes it useful for lifting heavy metal in scrapyards and factories, and for electric bells and motors.
63Describe the process of heating in a nichrome wire, and explain why conductors differ in resistance. [5]
Check answer
When current passes through a nichrome wire, the wire heats up because of its resistance to the flow of charge. Resistance is the property of a conductor that opposes the movement of electric charge.
Nichrome offers high resistance compared with copper of the same size and length, so a larger share of the electrical energy is converted into heat.
Conductors differ in resistance because of their material properties — atomic arrangement, structure, and how freely electrons can move through them. Nichrome's combination of high resistance and heat tolerance makes it an excellent heating element.
Nichrome offers high resistance compared with copper of the same size and length, so a larger share of the electrical energy is converted into heat.
Conductors differ in resistance because of their material properties — atomic arrangement, structure, and how freely electrons can move through them. Nichrome's combination of high resistance and heat tolerance makes it an excellent heating element.
64Fill in the blanks. [10]
(a) The heat produced by current flowing through a conductor also depends on the ______ of the electric current.
(b) The electrolyte in a dry cell is in the form of a ______.
(c) Hans Christian Oersted discovered the link between electricity and ______.
(d) The common rechargeable battery found in many devices today is the ______.
(e) Heavy iron scrap is fed into ______ at very high temperatures to make iron ingots and rods.
(f) Solid-state batteries replace liquid electrolytes with ______.
(g) The metal plates in a Voltaic cell are dipped in a liquid called an ______.
(h) When we increase the current through the coil, the magnet becomes ______.
(i) The heat generated in a wire depends on the material, thickness and ______ of the wire.
(j) If the direction of the flow of ______ is reversed, the poles of the electromagnet interchange.
(b) The electrolyte in a dry cell is in the form of a ______.
(c) Hans Christian Oersted discovered the link between electricity and ______.
(d) The common rechargeable battery found in many devices today is the ______.
(e) Heavy iron scrap is fed into ______ at very high temperatures to make iron ingots and rods.
(f) Solid-state batteries replace liquid electrolytes with ______.
(g) The metal plates in a Voltaic cell are dipped in a liquid called an ______.
(h) When we increase the current through the coil, the magnet becomes ______.
(i) The heat generated in a wire depends on the material, thickness and ______ of the wire.
(j) If the direction of the flow of ______ is reversed, the poles of the electromagnet interchange.
Check answer
(a) magnitude (b) paste (c) magnetism (d) lithium-ion battery (e) furnaces
(f) solid (g) electrolyte (h) stronger (i) length (j) current
(f) solid (g) electrolyte (h) stronger (i) length (j) current
The six ideas this whole chapter rests on
1. Heating effect: current meeting resistance turns electrical energy into heat. More resistance, more heat.2. Magnetic effect: current flowing through any conductor creates a magnetic field around it. No current, no field.
3. Oersted, 1820 discovered the link between electricity and magnetism by watching a compass needle move.
4. Electromagnet strength rises with more current, more coil turns, and a soft iron core — and it can be switched off.
5. Cells: Voltaic uses a liquid electrolyte, dry cell uses a paste, and both die when the chemicals are used up.
6. Nichrome is used for heating because it has high resistance and a high melting point; copper is used for wiring because it has low resistance.
Prepared by Sumeet Sahu at Unique Study Point, Indore, as per the latest NCERT syllabus for Session 2026-27. Download the PDF above to practise offline, then come back and check your answers here.
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