10th Students Magnetic effects of Electric Current

Answers to Science Questions

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 centred on the wire.

Answer: (d) The field consists of concentric circles centred on the wire.

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

(a) reduces substantially.

(b) does not change.

(c) increases heavily.

(d) vary continuously.

Answer: (c) increases heavily.

State whether the following statements are true or false.

(a) The field at the centre of a long circular coil carrying current will be parallel straight lines.

Answer: True

(b) A wire with a green insulation is usually the live wire of an electric supply.

Answer: False

List two methods of producing magnetic fields.

Answer: 1. By passing an electric current through a straight conductor. 2. By using a current-carrying coil or solenoid.

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

Answer: The force is largest when the current is perpendicular to the magnetic field.

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

Answer: Using the right-hand rule for the force on a negative charge, if the electron (negative) moves forward and is deflected right, the magnetic field must be upward (out of the page, toward the ceiling).

State the rule to determine the direction of a (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, and (iii) current induced in a coil due to its rotation in a magnetic field.

Answer: (i) Right-hand thumb rule: Curl fingers around the wire in the direction of current, thumb points to the magnetic field direction.

(ii) Fleming’s left-hand rule: Thumb (force), forefinger (magnetic field), middle finger (current) are perpendicular.

(iii) Fleming’s right-hand rule: Thumb (motion), forefinger (magnetic field), middle finger (induced current) are perpendicular.

When does an electric short circuit occur?

Answer: An electric short circuit occurs when live and neutral wires come into direct contact, often due to damaged insulation, causing a sudden increase in current.

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

Answer: The earth wire provides a path for excess current to flow into the ground, preventing electric shocks. It is necessary to earth metallic appliances to protect users from lethal shocks if a fault causes the metal to become live.