Question

5.    Briefly describe the main physics principles involved in the way each of the following works, making sure to tell how magnetic forces or magnetic fields are involved :   

             a. a galvanometer     

             b. an electric motor

c. a generator

Answer 1

(a) Galvenometer: The galvanometer is an instrument used to determine the presence, direction, and strength of an electric current in a conductor.

Principle: Galvanometer works on the principle of conversion of electrical energy into mechanical energy.

When a current flows in a magnetic field, it experiences a magnetic torque.

If it is free to rotate under a controlling torque, it rotates through an angle proportional to the current flowing through it.

A galvanometer is a type of ammeter. It is an instrument for detecting and measuring electric current.

(b) An electric motor :

A motor is an electrical machine which converts electrical energy into mechanical energy. The principle of working of a DC motor is that "whenever a current carrying conductor is placed in a magnetic field, it experiences a mechanical force".

The functioning principle of the electric motor is based on the fact that a current carrying conductor produces a magnetic field around it. Imagine the following situation.

Take two bar magnets and keep the poles facing each other with a small space in between. Now take a small length of a conducting wire and make a loop. Keep this loop in between the space between the magnets such that is still within the sphere of influence of the magnets. Now for the last bit. Connect the ends of the loop to battery terminals.

Once electricity flows through your simple circuit you will notice that your loop “moves”. So why does this happen? The magnetic field of the magnets interfere with that produced due to electric current flowing in the conductor. Since the loop has become a magnet, one side of it will be attracted to the north pole of the magnet and the other to the south pole. This causes the loop to continuously rotate. This is the principle of working of an electric motor.

(c) A generator :

Principle of working of an electric generator:

Electric generator is an application of electromagnetic induction.

Electric generator works on the principle that when a straight conductor is moved in a magnetic field, then current is induced in the conductor

In an electric generator a rectangular coil is made to rotate rapidly in the magnetic field between the poles of a horseshoe type magnet. When the coil rotates it cut the magnetic field lines due to which current is produced in the coil .