Clock Face Rule

A current carrying loop works like a disc magnet. The polarity of this magnet can be easily understood with the help of clock face rule. If the current is flowing in anti-clockwise direction, then the face of the loop shows north pole. On the other hand, if the current is flowing in clockwise direction, then the face of the loop shows south pole. The figure on the left hand side shows anti-clockwise current and North Pole. The figure on the right hand side shows clockwise current and South Pole.

Magnetic field and number of turns of coil

Magnitude of magnetic field gets summed up with increase in the number of turns of coil. If there are n turns of coil, magnitude of magnetic field will be n times of magnetic field in case of a single turn of coil.

Magnetic Field due to a current in a Solenoid:

Solenoid is the coil with many circular turns of insulated copper wire wrapped closely in the shape of a cylinder. In other words, a solenoid is a device which converts electrical energy into magnetic force. The term solenoid was coined by Andre Marie Ampere in 1823.

A current carrying solenoid produces similar pattern of magnetic field as a bar magnet. One end of solenoid behaves as the north pole and another end behaves as the south pole. Magnetic field lines are parallel inside the solenoid, similar to a bar magnet. It shows that magnetic field is same at all points inside the solenoid.

By producing a strong magnetic field inside the solenoid, magnetic materials can be magnetized. Magnet formed by producing magnetic field inside a solenoid is called electromagnet.

Uses of Solenoid

Solenoid or electromagnet is used in many devices. It is used in call bell. It is used in electric motor. In fact, a solenoid is used wherever a controlled magnetic field is required.