Ram is a student of class `X` in a village school. His uncle gifted him a bicycle with a dynomo fifted in it. He was very excited to get it. While cycling during night, he could light the bulb and see the objects on the road. He, however, did not know how this device works. He asked this questions to his teacher. The teacher considered it an opprtunity to explain the working to the whole class.
Answer the following questions :
`(i)` State the principle and working of dynamo.
`(ii)` Write two values each displayed by Ram and his school teacher.

Explanation

`(i)` Principle : It works on the principle of electromagnetic induction. When a coil is rotated in a magnetic field, magnetic flux linked to it changes continuously giving rise to an alternating emf.
Working : When the armature coil is rotated in the strong magnetic field, the magnetic flux linked with the coil changes and the current is induced in the coil. Considering the armature of be in vertical position and as it rotates in anticlock wise direction, the side ab moves upward and cd downward, so that the direction of induced current is shown in fig. In the circuit, the current flows along `B_(1)`, `R_(1)`, `B_(2)`. The direction of current remains unchanged during the first half turn of armature. During the second half revolution, the wire ab moves downward and cd upward, so the direction of current it reversed and in external circuit it flows along `B_(2)R_(l)B_(1)`. Thus, the direction of induced emf and current changes in the external circuit after each half revoluation.
`(ii)` Ram is very curious to know, quest for knowledge. Teacher is very helping and having good knowledge of science.