CBSE Class 10 Science Magnetic Effects of Electric Current Assignment Set 10

This Class 10 Science assignment for the chapter Magnetic Effects of Electric Current gives 13 mixed practice questions on electromagnetic induction, induced current in coils, alternating current, domestic circuits and safety devices, with marks shown against each question. Every answer is written step by step with a simple-words line and a teacher's note.

Very Short Answer Questions (1 Mark)

Question 1. Name the phenomenon in which a changing magnetic field around a coil produces an electric current in it. (1 mark)
Answer:
The phenomenon is electromagnetic induction.
In simple words: Changing field produces current in a coil.

Teacher's Note:
1. Discovered by Michael Faraday.
2. Use the full term.

Question 2. What is meant by induced electric current? (1 mark)
Answer:
The current produced in a conductor or coil when the magnetic field around it changes (or when there is relative motion between the coil and a magnet) is called an induced current.
In simple words: A current set up by a changing magnetic field.

Teacher's Note:
1. Include the reason for its production.
2. It lasts only while the change continues.

Question 3. What does Fleming's right-hand rule give: the magnitude or the direction of the induced current? (1 mark)
Answer:
It gives the direction of the induced current.
In simple words: Right-hand rule: direction of induced current.

Teacher's Note:
1. Remember: left hand is for motors, right hand is for generators.
2. It does not give magnitude.

Question 4. What is the function of a galvanometer in a circuit? (1 mark)
Answer:
A galvanometer detects the presence of an electric current in a circuit, and its pointer deflects to the left or right depending on the direction of the current.
In simple words: It detects small currents.

Teacher's Note:
1. Zero is at the centre of the scale.
2. It does not measure large currents.

Question 5. At the time of a short circuit, what happens to the electric current in the circuit? (1 mark)
Answer:
The live and the neutral wire come into direct contact, so the resistance falls to almost zero and the current in the circuit increases heavily.
In simple words: Current becomes very large in a short circuit.

Teacher's Note:
1. Link to Ohm's law: low resistance means large current.
2. This is why fuses are used.

Short Answer Questions (2 and 3 Marks)

Question 6. Write two ways to induce a current in a coil. (2 marks)
Answer:
(i) By moving a bar magnet towards or away from the coil.
(ii) By placing the coil near another coil connected to a battery and changing the current in that coil (for example by opening or closing the key).
In simple words: Moving a magnet or changing a nearby current induces current.

Teacher's Note:
1. Give two different ways.
2. Any change in field linked with the coil is enough.

Question 7. Name two safety measures commonly used in electric circuits and appliances. What precaution should be taken to avoid overloading of domestic circuits? (2 marks)
Answer:
Two safety measures: the electric fuse and the earth wire (earthing of metal bodies).
To avoid overloading: do not connect many high-power appliances to the same socket, and use fuses or MCBs of proper rating.
In simple words: Fuse and earthing protect; do not overload sockets.

Teacher's Note:
1. Name two devices.
2. Give one clear precaution.

Question 8. In Faraday's experiment, if we move the coil towards the magnet instead of moving the magnet towards the coil, will there be an induced current? Justify and compare the two cases. (3 marks)
Answer:
Yes. What matters is the relative motion between the coil and the magnet, because it changes the magnetic field linked with the coil.
In both cases a current is induced, with the same magnitude for the same relative speed, and the galvanometer deflects in the same direction.
In simple words: Relative motion is what induces the current.

Teacher's Note:
1. State that only relative motion matters.
2. Compare both cases in one line.

Question 9. Two circular coils P and Q are placed close to each other and P carries a current. What will the galvanometer connected across Q show if the current in P is changed? Give a reason. (3 marks)
Answer:
The galvanometer shows a deflection while the current in P is changing.
Changing the current in P changes the magnetic field around it, so the field linked with Q changes and a current is induced in Q.
If the current in P is steady, the galvanometer shows no deflection.
In simple words: A changing current in P induces a current in Q.

Teacher's Note:
1. The reason is the change in linked field.
2. A steady current gives no induced current.

Question 10. Two coils of insulated copper wire are wound over a non-conducting cylinder. Coil 1 is connected to a battery through a key and coil 2 to a galvanometer. What is observed when the key is (i) closed, (ii) opened? Give a reason. (3 marks)
Answer:
(i) When the key is closed, the galvanometer shows a momentary deflection in one direction, because the current in coil 1 rises from zero and its magnetic field changes.
(ii) When the key is opened, there is a momentary deflection in the opposite direction, because the current in coil 1 falls to zero and the field changes the other way.
In both cases the changing field linked with coil 2 induces a current in it.
In simple words: Switching on and off gives deflections in opposite directions.

Teacher's Note:
1. Mention that deflection is only momentary.
2. State the opposite directions.

Question 11. Give reasons: (a) It is dangerous to touch the live wire rather than the neutral wire. (b) Household appliances are connected in parallel. (c) A fuse is important in a household circuit. (3 marks)
Answer:
(a) The live wire is at 220 V while the neutral wire is at about zero volt, so touching the live wire gives a shock.
(b) Each appliance gets the same voltage, can be switched separately, and one failure does not stop the others.
(c) The fuse is connected in series with the live wire and melts to cut off the supply during a short circuit or overloading, protecting appliances.
In simple words: Live wire carries the voltage; parallel wiring and a fuse give safety.

Teacher's Note:
1. Write one sentence per part.
2. Note the fuse is in series.

Question 12. Fuse acts like a watchman in an electric circuit. Justify. Mention the usual rating of the fuse used for (i) lights and fans, (ii) appliances of 2 kW or more. (3 marks)
Answer:
When an unusually large current flows, the fuse wire melts because of the heating effect of current and breaks the circuit. So it keeps watch on the current and cuts it off when it exceeds the safe value.
(i) A fuse of 5 A is used for lights and fans.
(ii) A fuse of 15 A is used for appliances of 2 kW or more.
In simple words: The fuse melts and cuts off the circuit when the current is too high.

Teacher's Note:
1. Mention the heating effect.
2. Give the numerical ratings.

Long Answer Questions (5 Marks)

Question 13. A coil of insulated copper wire is connected to a galvanometer. A bar magnet with its south pole towards one face of the coil is (i) moved quickly towards the coil, (ii) moved quickly away from it, (iii) held near the face of the coil. State what is observed in each case and name the phenomenon involved. (5 marks)
Answer:
(i) The galvanometer needle shows a deflection in one direction, since the magnetic field linked with the coil increases and a current is induced.
(ii) The needle deflects in the opposite direction, since the linked field decreases.
(iii) There is no deflection, because the field linked with the coil is not changing.
The phenomenon is electromagnetic induction.
A faster motion of the magnet gives a larger deflection.
In simple words: Moving the magnet induces a current; keeping it still does not.

Teacher's Note:
1. Mention that the deflection is in opposite directions in (i) and (ii).
2. Name the phenomenon at the end.