Chapter 13: Magnetic Effects of Electric Current

Why does a compass needle get deflected when brought near a bar magnet?

Draw magnetic field lines around a bar magnet.

List the properties of magnetic lines of force.

Why don't two magnetic lines of force intersect each other?

Consider a circular loop of wire lying in the plane of the table. Let the current pass through the loop clockwise. Apply the right-hand rule to find the direction of the magnetic field inside and outside the loop.

The magnetic field in a given region is uniform. Draw a diagram to represent it.

Choose the correct option. The magnetic field inside a long straight solenoid-carrying current (a) is zero (b) decreases as we move towards its end (c) increases as we move towards its end (d) is the same at all points.

Which of the following property of a proton can change while it moves freely in a magnetic field? (There may be more than one correct answer.) (a) mass (b) speed (c) velocity (d) momentum

In Activity 13.7 (NCERT), how do we think the displacement of rod AB will be affected if (i) current in rod AB is increased; (ii) a stronger horse-shoe magnet is used; (iii) length of rod AB is increased?

A positively-charged particle (alpha-particle) projected towards west is deflected towards north by a magnetic field. The direction of magnetic field is (a) towards south (b) towards east (c) downward (d) upward.

State Fleming's left-hand rule.

What is the principle of an electric motor?

What is the role of the split ring in an electric motor?

Explain different ways to induce current in a coil.

State the principle of an electric generator.

Name some sources of direct current.

Which sources produce alternating current?

Choose the correct option. A rectangular coil of copper wires is rotated in a magnetic field. The direction of the induced current changes once in each (a) two revolutions (b) one revolution (c) half revolution (d) one-fourth revolution.

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.

The phenomenon of electromagnetic induction is (a) the process of charging a body. (b) the process of generating magnetic field due to a current passing through a coil. (c) producing induced current in a coil due to relative motion between a magnet and the coil. (d) the process of rotating a coil of an electric motor.

The device used for producing electric current is called a (a) generator (b) galvanometer (c) ammeter (d) motor.

The essential difference between an AC generator and a DC generator is that (a) AC generator has an electromagnet while DC generator has a permanent magnet. (b) DC generator will generate a higher voltage. (c) AC generator will generate a higher voltage. (d) AC generator has slip rings while DC generator has a commutator.

At the time of short circuit, the current in the circuit (a) reduces substantially (b) does not change (c) increases heavily (d) varies continuously.

State whether the following statements are true or false. (a) An electric motor converts mechanical energy into electrical energy. (b) An electric generator works on the principle of electromagnetic induction. (c) The field at the centre of a long circular coil carrying current is uniform. (d) A wire with current in a magnetic field experiences a force.

List three sources of magnetic fields.

How does a solenoid behave like a magnet? Can you determine the north and south poles of a current-carrying solenoid with the help of a bar magnet? Explain.

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

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 the magnetic field?

Draw a labelled diagram of an electric motor. Explain its principle and working. What is the function of a split ring in an electric motor?

Name some devices in which electric motors are used.

A coil of insulated copper wire is connected to a galvanometer. What will happen if a bar magnet is (i) pushed into the coil, (ii) withdrawn from inside the coil, (iii) held stationary inside the coil?

Two circular coils A and B are placed close to each other. If the current in coil A is changed, will some current be induced in coil B? Give reason.

State the rule to determine the direction of a (i) magnetic field produced around a current-carrying conductor, (ii) force experienced by a current-carrying conductor placed in a magnetic field, (iii) current induced in a coil due to its rotation in a magnetic field.

What is an electromagnet? Give two uses.

Differentiate between direct current and alternating current.