E X E R C I S E S CHAPTER 12 Magnetic Effects of Electric Current SCIENCE NCERT TEXTBOOK (CBSE) CLASS 10:

 E X E R C I S E S  

CHAPTER  12  Magnetic Effects of  Electric Current 


1. Which of the following correctly describes the magnetic field near a long straight wire?

  • (a) The field consists of straight lines perpendicular to the wire.
  • (b) The field consists of straight lines parallel to the wire.
  • (c) The field consists of radial lines originating from the wire.
  • (d) The field consists of concentric circles centered on the wire.

Answer: (d) The field consists of concentric circles centered on the wire.
Explanation: The magnetic field around a long straight current-carrying wire forms concentric circles centered on the wire. The direction of the field is given by the right-hand thumb rule.

2. At the time of short circuit, the current in the circuit:

  • (a) reduces substantially.
  • (b) does not change.
  • (c) increases heavily.
  • (d) varies continuously.

Answer: (c) increases heavily.
Explanation: In the case of a short circuit, the resistance in the circuit becomes very low, leading to a large current, which can cause damage or heating.

3. State whether the following statements are true or false:

  • (a) The field at the center of a long circular coil carrying current will be parallel straight lines.
  • (b) A wire with a green insulation is usually the live wire of an electric supply.

Answer:

  • (a) True. The magnetic field at the center of a long circular coil (solenoid) is uniform and parallel to the axis of the coil.
  • (b) False. A wire with green insulation is usually the earth wire (ground), not the live wire. The live wire is typically color-coded red or brown.

4. List two methods of producing magnetic fields.

Answer:

  1. Electric current through a wire: When an electric current flows through a conductor, it generates a magnetic field around it.
  2. Using a permanent magnet: Permanent magnets, like bar magnets, generate a magnetic field naturally without the need for any external power source.

5. When is the force experienced by a current-carrying conductor placed in a magnetic field largest?

Answer: The force is largest when the current-carrying conductor is perpendicular to the magnetic field.
Explanation: The force experienced by the conductor is given by F=BILsin⁡θF = BIL \sin \theta, where θ\theta is the angle between the magnetic field and the current. The force is maximum when θ=90∘\theta = 90^\circ (i.e., the conductor is perpendicular to the magnetic field).

6. Imagine that you are sitting in a chamber with your back to one wall. An electron beam, moving horizontally from the back wall towards the front wall, is deflected by a strong magnetic field to your right side. What is the direction of the magnetic field?

Answer: The magnetic field is directed out of the chamber (towards you).
Explanation: Using the right-hand rule for the direction of force on a moving electron (which has a negative charge), the force on the electron beam is to the right, which means the magnetic field must be directed towards the observer (out of the chamber) to produce this effect.

7. State the rule to determine the direction of:

  • (i) Magnetic field produced around a straight conductor carrying current.
  • (ii) Force experienced by a current-carrying straight conductor placed in a magnetic field which is perpendicular to it.
  • (iii) Current induced in a coil due to its rotation in a magnetic field.

Answer:

  • (i) Right-hand thumb rule: Point your right-hand thumb in the direction of the current, and your fingers will curl around the conductor in the direction of the magnetic field.
  • (ii) Fleming’s Left-Hand Rule: Place your left hand such that the thumb, first finger, and second finger are all perpendicular to each other. The thumb gives the direction of the force, the first finger gives the direction of the magnetic field, and the second finger gives the direction of the current.
  • (iii) Fleming's Right-Hand Rule: Point the thumb of your right hand in the direction of the motion of the conductor, the first finger in the direction of the magnetic field, and the second finger will point in the direction of the induced current.

8. When does an electric short circuit occur?

Answer: An electric short circuit occurs when there is a low-resistance connection between the live and neutral wires, bypassing the normal load. This causes an excessive current to flow, which can damage the circuit and lead to overheating or fires.

9. What is the function of an earth wire? Why is it necessary to earth metallic appliances?

Answer:

  • Function of an earth wire: The earth wire provides a safe path for electric current to flow to the ground in case of a fault, such as when the live wire comes into contact with a metal part of an appliance.
  • Why is it necessary to earth metallic appliances? It is necessary to earth metallic appliances to prevent electric shocks. If there is a fault in the appliance, the metal body can become live, and earthing ensures that the current safely flows to the ground instead of through a person touching the appliance.

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