The magnetic field lines inside a solenoid are :

1. parallel and circular
2. straight and parallel to the axis of solenoid
3. straight and perpendicular to the axis of solenoid
4. circular

On reversing the direction of current in a wire, the magnetic field produced by it:

1. gets reversed in direction
2. increases in strength
3. decreases in strength
4. remains unchanged in strength and direction.

Horse shoe magnets are used in :

1. d.c. motor
2. a.c. generator
3. electric bell
4. all of the above

How is magnetic field due to a straight current carrying wire affected if current in wire is (a) decreased, (b) reversed?