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A transformer is a device which increase...

A transformer is a device which increases or decreases alternating voltage through mutual induction. It consists of two coils wound on the same code. One of the coil is connected to input alternating supply. This is called primary coil. The other coil gives the output. i.e. it is connected to external load. This coil is called secondary coil. The alternating emf applied across the primary current causes an alternating current to flow through it. This alternating current creates a continuously changing magnetic flux through the core. The changing magnetic flux is linked with secondary coil. If there is no leakage of flux, then the flux linked per unit turn with primary coil is equal to the flux linked per unit turn with secondary coil. Let `phi_(S)` is flux linked in secondary coil and `phi_(P)` is flux linked in primary coil then `(phi_(S))/(N_(S))=(phi_(P))/(N_(P))` (where `N_(S)` and `N_(P)` are respective number of turns in secondary and primary of transformer)
`:. (1)/(N_(s))(d phi_(S))/(dt)=(1)/(N_(P))xx(d phi_(P))/(dt)`
or `(1)/(N_(S)) E_(S)=(1)/(N_(P))E_(P)` (`:' E = - (d phi)/(dt) = ` emf in a coil )
If the voltage in secondary is more than that in primary, the transformer is step-up. If voltage in secondary is less than that in primary, the transformer is called step down. Select the correct alternative

A

For step-up transformer `N_(S) gt N_(P)`

B

For a step-up transformer `N_(S) lt N_(P)`

C

For a step-down transformer `N_(S) gt N_(P)`

D

For a step-down transformer `N_(S)=N_(P)`

Text Solution

Verified by Experts

The correct Answer is:
A
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