# Investigatory Project on Solenoid

Investigatory Project on Solenoid and the Magnet

Aim: To study the variation of force of attraction between a solenoid and a bar magnet with the current flowing through the solenoid.

Materials and apparatus required: A short solenoid of thin insulated copper wire having a large number of turns wound over a pvc pipe of radius about 0.5 cm and length about 3 cm, a bar magnet, a 4-volt battery, a rheostat, an ammeter, a accumulator, common balance, etc.

Principle:

A current carrying solenoid acts like a bar magnet. The strength of the magnetic field along its axis due to the current through a solenoid depends on (1) the current i flowing through the solenoid and (2) the number of turns per unit length n of the solenoid. As a result of it, the force of interaction between a bar magnet and the current carrying solenoid can be changed by (1) varying current and (2) varying the distance between them.

Experimental set up:

The bar magnet is suspended vertically from the stirrup at one of the ends of the beam of the common balance after removing the pan from there. The other pan is left as it is and weight are added in this pan to counter balance the weight of the magnet. The solenoid is placed just below the magnet such that the axis of the solenoid coincide with the axis of the bar magnet. The distance between the lower end of the magnet and the upper end of the solenoid should be kept constant.

The solenoid is connected in series with the battery, rheostat and ammeter through a commutator.

Procedure

The commutator is put in one direction and the rheostat is adjusted to send a suitable current. If there is a repulsion between the solenoid and the magnet, reverse the direction of current through the solenoid using the commutator to make the force attractive. Weights are added in the pan to balance the attractive force between the solenoid and the bar magnet. The additional weight m added in the pan is noted. Repeat the experiment for different values of current.

A graph is drawn taking the force of attraction, F = mg, along the y-axis and the current along the x-axis. The graph is a straight line.

Observations

 Trial Ammeter reading i(A) Weight added in the pan m(kg) Force of attraction, F = mg(N) 1 2 3 4 ….

Conclusion

The straight line graph shows that the force (F) of attraction between the current carrying solenoid and the bar magnet is directly proportional to the current (i) passing through the solenoid.