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Question

The transformation ratio in the step-up transformer is


A

one

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B

greater than one

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C

less than one

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D

the ratio greater or less than one depends on the other factors

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Solution

The correct option is B

greater than one


Explanation for the correct answer:-

Option (B)

Step 1: Formula Used,
Transformation Ratio = VsVp=N2N1

Vs=N2dϕdt, Vp=N1dϕdt

dϕdt is the rate of change of magnetic flux.

The number of turns in the primary coil is N1and the number of turns in the secondary coil is N2.

Vp= Primary voltage

Vs= Secondary voltage

Step 2: Calculating the transformation ratio in the step-up transformer,

The transformer consists of two coils wound on a soft-core. They are completely insulated from each other.

The number of turns on these coils are not the same. The number of turns in the primary coil is N1and the number of turns in the secondary coil is N2.
When the input voltage Vpis applied on the input coil, emf is generated on the second coil due to mutual inductance.
Vs=N2dϕdt
where dϕdt is the rate of change of magnetic flux.
Due to change in the magnetic flux linked to the same coil an emf is induced in the primary coil. This is called a back emf.
Vp=N1dϕdt
Thus,
VsVp=N2N1
This implies that the induced voltage in the secondary coil depends on the ratio of turns in the 2 coils. This ratio is called the transformation ratio.
In a step-up transformer, the output voltage is greater than the input voltage.

In such cases, the transformation ratio,
VsVp=N2N1>1
Hence, the correct option is Option B.


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