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Class 8 Science Chapter 4 – Electricity: Magnetic and Heating Effects | NCERT Curiosity Worksheet

Practise Class 8 Science Chapter 4 – Electricity: Magnetic and Heating Effects with this easy NCERT Curiosity worksheet. Includes important questions and revision exercises to strengthen understanding of electricity, magnetic effects and heating effects and prepare effectively for class tests and exams.

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Class 8 Science – Chapter 4

Electricity: Magnetic and Heating Effects

Fresh Practice Worksheet

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Instructions

  • Read each question carefully.
  • Answer in simple and complete sentences.
  • Draw neat diagrams wherever required.
  • For numerical or reasoning questions, show the important steps.

Section A – Multiple Choice Questions

1. What happens to the needle of a magnetic compass when it is placed near a current-carrying wire?
(a) It melts
(b) It deflects
(c) It becomes heavier
(d) It stops being a magnet
2. Which of the following is used to make an electromagnet stronger?
(a) Removing the iron core
(b) Reducing the number of turns
(c) Increasing the number of turns
(d) Stopping the current
3. Which material is commonly used as a heating element?
(a) Copper
(b) Nichrome
(c) Silver
(d) Aluminium
4. An electromagnet can be switched off by:
(a) increasing its length
(b) stopping the electric current
(c) adding more iron
(d) increasing the number of poles
5. Which part of a simple dry cell acts as the negative terminal?
(a) Carbon rod
(b) Zinc container
(c) Electrolyte
(d) Metal cap
6. Which of the following is a rechargeable battery application?
(a) Mobile phone
(b) Ordinary single-use dry cell
(c) Lemon
(d) Voltaic cell only
7. Which effect of electric current is mainly used in an electric iron?
(a) Magnetic effect
(b) Heating effect
(c) Chemical effect only
(d) Gravitational effect
8. What happens when the direction of current through an electromagnet is reversed?
(a) Its poles are reversed
(b) It stops conducting forever
(c) Its iron core disappears
(d) It becomes a dry cell
9. Which substance acts as the electrolyte in a lemon cell?
(a) Copper wire
(b) Iron nail
(c) Lemon juice
(d) LED
10. Which scientist discovered the connection between electric current and magnetism using a compass?
(a) Alessandro Volta
(b) Hans Christian Oersted
(c) Alexander Fleming
(d) Edward Jenner

Section B – Fill in the Blanks

1. A current-carrying coil that behaves like a magnet is called an .
2. The region around a current-carrying conductor where its magnetic effect can be felt is called a .
3. wire is commonly used in electric heating appliances.
4. The production of heat due to the flow of electric current is called the effect of electric current.
5. A Voltaic cell uses a liquid called an .
6. A cell that can no longer supply electricity is called a cell.
7. The zinc container of a dry cell acts as the terminal.
8. Rechargeable batteries can be charged and many times.
9. An iron core makes an electromagnet .
10. The magnetic effect of electric current disappears when the electric stops.

Section C – True or False

1. Electric current flowing through a wire can produce a magnetic field.
2. An electromagnet cannot be switched off.
3. Increasing the number of turns of a coil can increase the strength of an electromagnet.
4. Nichrome has greater resistance than copper of the same size and length.
5. All batteries can be recharged.
6. A dry cell has a thick moist paste as its electrolyte.
7. Reversing the current direction can reverse the poles of an electromagnet.
8. A compass needle is a tiny magnet.
9. An iron core generally makes an electromagnet weaker.
10. Used batteries should be disposed of carefully because they may contain harmful materials.

Section D – Match the Following

Column AColumn B
1. ElectromagnetA. Thick moist paste
2. NichromeB. Produces a magnetic field when current flows
3. Zinc containerC. Common heating element
4. Dry cell electrolyteD. Negative terminal
5. Lemon juiceE. Electrolyte in a lemon cell

Section E – Very Short Answer Questions

1. What does a compass show when placed near a current-carrying wire?
2. What is an electromagnet?
3. Name one appliance that works using the heating effect of electric current.
4. Why is an iron core used in an electromagnet?
5. What is an electrolyte?
6. What is meant by a dead cell?
7. Name the scientist associated with the discovery of the magnetic effect of electric current using a compass.
8. Name one rechargeable battery device used in daily life.

Section F – Short Answer Questions

1. Explain why a compass needle deflects when placed near a current-carrying wire.
2. Write any three ways of increasing the strength of an electromagnet.
3. Why does an electromagnet lose its magnetic effect when the switch is turned OFF?
4. Why is nichrome used in electric heaters and irons?
5. Differentiate between a dry cell and a rechargeable battery.
6. Explain how a lemon can be used to make a simple electric cell.

Section G – Give Reasons

1. An iron core is placed inside many practical electromagnets.
2. An electric iron becomes hot when switched ON.
3. A compass can be used to detect the magnetic effect of electric current.
4. A dry cell is called a single-use cell.
5. Battery recycling is important.

Section H – Application-Based Questions

1. Rohan makes an electromagnet using a coil and an iron nail. His electromagnet can lift only three paper clips. Suggest two changes that may help him make it stronger.
2. A student connects a coil to a battery and places a compass near it. The compass needle deflects. What does this observation tell us?
3. An electric heater is connected to a power source. After some time its heating element becomes very hot. Which effect of electric current is being observed?
4. A student reverses the terminals of the battery connected to an electromagnet. What change would you expect in the electromagnet?
5. A mobile phone battery can be charged again and again. What type of battery is it?

Section I – Case-Based Question 1

Case: Aarav makes an electromagnet by winding insulated wire around an iron nail. He connects the coil to one cell and observes that it attracts a few paper clips. He then increases the number of turns and connects the coil to a stronger battery.
(a) Why does the iron nail attract paper clips?
(b) What happens when the current is switched OFF?
(c) Why does increasing the number of turns help?
(d) Why can a battery with more cells make the electromagnet stronger?

Section J – Case-Based Question 2

Case: Meera compares copper wire and nichrome wire. She connects them separately in a circuit and allows current to flow for the same amount of time. She notices that the nichrome wire becomes hotter.
(a) Which wire offers greater resistance?
(b) Which effect of electric current is observed?
(c) Why is nichrome useful in heating appliances?
(d) Name two appliances that use a heating element.

Section K – Compare and Differentiate

1. Differentiate between magnetic effect and heating effect of electric current.
2. Differentiate between a Voltaic cell and a dry cell.
3. Differentiate between a single-use cell and a rechargeable battery.

Section L – Think and Answer

1. A coil is connected to a cell but no iron nail is placed inside it. Will the coil still have a magnetic effect? Explain.
2. Why does increasing the number of turns of a coil generally increase the strength of an electromagnet?
3. What would happen to the compass needle if the current through the nearby wire is switched OFF?
4. Why should an electrical appliance not be allowed to overheat?
5. Why should used batteries not simply be thrown into household garbage?

Section M – HOTS Questions

1. Two students make identical electromagnets. One uses one cell and the other uses two cells. Which electromagnet is expected to have a stronger magnetic effect? Why?
2. A student wants to make the poles of an electromagnet change. What should the student do?
3. Why can an electromagnet be more useful than a permanent magnet in a scrap yard crane?
4. An electric appliance has a heating element. What may happen if too much current passes through it for a long time?
5. Why is the magnetic effect of a current-carrying coil useful in lifting heavy iron objects?

Section N – Challenge Questions

1. A student wants an electromagnet to lift more paper clips. Write a simple experiment that can be used to investigate whether increasing the number of turns makes the electromagnet stronger.
2. Suppose a lemon cell does not light an LED. Give two possible things the student could check.
3. Why can a current-carrying wire produce both magnetic and heating effects at the same time?
4. Explain why changing the direction of current changes the poles of an electromagnet.
5. A battery has stopped working after being used many times. Does this always mean that every material inside it has no further value? Explain briefly.

Section O – Diagram and Activity Questions

1. Draw a simple circuit showing a cell, switch and a coil wound around an iron nail. Label the important parts.
2. Draw a simple diagram of a lemon cell and label the copper electrode, iron electrode and electrolyte.
3. Draw a magnetic compass near a current-carrying straight wire and show the expected deflection.
4. Draw and label a simple dry cell showing its zinc container, carbon rod and electrolyte.

Answer Key

Section A – Multiple Choice Questions

  1. (b) It deflects
  2. (c) Increasing the number of turns
  3. (b) Nichrome
  4. (b) Stopping the electric current
  5. (b) Zinc container
  6. (a) Mobile phone
  7. (b) Heating effect
  8. (a) Its poles are reversed
  9. (c) Lemon juice
  10. (b) Hans Christian Oersted

Section B – Fill in the Blanks

  1. electromagnet
  2. magnetic field
  3. Nichrome
  4. heating
  5. electrolyte
  6. dead
  7. negative
  8. reused
  9. stronger
  10. current

Section C – True or False

  1. True
  2. False
  3. True
  4. True
  5. False
  6. True
  7. True
  8. True
  9. False
  10. True

Section D – Match the Following

Column AAnswer
1. ElectromagnetB. Produces a magnetic field when current flows
2. NichromeC. Common heating element
3. Zinc containerD. Negative terminal
4. Dry cell electrolyteA. Thick moist paste
5. Lemon juiceE. Electrolyte in a lemon cell

Section E – Very Short Answers

  1. The compass needle deflects.
  2. An electromagnet is a current-carrying coil that behaves like a magnet.
  3. Electric iron.
  4. It makes the electromagnet stronger.
  5. An electrolyte is a substance that helps in producing and conducting electricity inside a cell.
  6. A cell that can no longer supply electricity.
  7. Hans Christian Oersted.
  8. Mobile phone.

Section F – Short Answers

  1. A current-carrying wire produces a magnetic field. This magnetic field affects the compass needle and makes it deflect.
  2. Increase the current, increase the number of turns and use an iron core.
  3. The magnetic field is produced by electric current. When current stops, the magnetic effect disappears.
  4. Nichrome has relatively high resistance and produces considerable heat when current flows through it.
  5. A dry cell is generally used once, while a rechargeable battery can be charged and reused many times.
  6. Insert a copper wire and an iron nail into a lemon without letting them touch. The lemon juice acts as an electrolyte and the two metals act as electrodes.

Section G – Give Reasons

  1. An iron core makes the electromagnet stronger.
  2. Electric current produces heat as it passes through the heating element.
  3. A current-carrying wire produces a magnetic field, which deflects the compass.
  4. The chemicals in a single-use dry cell get used up and it cannot normally be recharged.
  5. Used batteries may contain harmful materials and valuable materials that can be recycled.

Section H – Application-Based Answers

  1. Increase the number of turns and use more current, such as a suitable battery with more cells.
  2. It shows that electric current produces a magnetic field.
  3. The heating effect of electric current.
  4. The poles of the electromagnet will reverse.
  5. A rechargeable battery.

Section I – Case-Based Question 1

  1. The current-carrying coil magnetises the iron nail.
  2. The magnetic effect disappears and the clips fall off.
  3. More turns produce a stronger magnetic effect.
  4. A battery with more cells can provide a larger current, producing a stronger magnetic field.

Section J – Case-Based Question 2

  1. Nichrome wire.
  2. Heating effect of electric current.
  3. It has relatively high resistance and produces more heat.
  4. Electric iron and electric heater.

Section K – Compare and Differentiate

1. Magnetic effect and heating effect:

  • Magnetic effect: Current produces a magnetic field.
  • Heating effect: Current produces heat in a conductor.

2. Voltaic cell and dry cell:

  • Voltaic cell uses an electrolyte that is usually a liquid.
  • Dry cell uses a thick moist paste as its electrolyte.

3. Single-use cell and rechargeable battery:

  • A single-use cell is normally used once.
  • A rechargeable battery can be charged and reused many times.

Section L – Think and Answer

  1. Yes. A current-carrying coil can produce a magnetic field even without an iron nail. The iron nail only makes the magnetic effect stronger.
  2. More turns produce a stronger magnetic effect under similar conditions.
  3. The compass needle returns towards its original direction.
  4. Overheating may damage the appliance and can create a fire risk.
  5. Used batteries may contain harmful substances and should be properly recycled.

Section M – HOTS Answers

  1. The electromagnet with two cells is expected to be stronger because a larger current can produce a stronger magnetic field.
  2. Reverse the direction of current through the coil by reversing the battery terminals.
  3. It can be switched ON and OFF, allowing the crane operator to pick up and release objects easily.
  4. The appliance may become excessively hot and may be damaged or create a fire risk.
  5. The magnetic field of the electromagnet can attract and lift iron objects.

Section N – Challenge Answers

  1. Make coils with different numbers of turns, connect each to the same cell, and count how many paper clips each coil can lift. Compare the results.
  2. Check the connections and make sure the LED is connected in the correct direction. Also check that the electrodes are properly inserted into the lemon.
  3. Current flowing through a conductor can produce a magnetic field, while the resistance of the conductor converts some electrical energy into heat.
  4. Changing the direction of current changes the direction of the magnetic field around the coil, so its poles are reversed.
  5. No. Some materials inside batteries can still be valuable and recyclable, while some may be harmful if disposed of incorrectly.

Section O – Diagram and Activity Questions

1. The diagram should show a cell, switch, connecting wires and a coil wound around an iron nail.

2. The diagram should show a lemon with a copper electrode, iron electrode and lemon juice as the electrolyte.

3. The diagram should show the compass needle changing direction when current flows through the nearby wire.

4. The diagram should label the zinc container, carbon rod and electrolyte.

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