Physics

Alternating Current

Transformer

(a) Describe, with the help of a suitable diagram, the working

Question

Easy

Solving time: 2 mins

(a) Describe, with the help of a suitable diagram, the working principle of a step-up transformer. Obtain the relation between input and output voltages in terms of the number of turns of primary and secondary windings and the currents in the input and output circuits.
(b) Given the input current 15 A and the input voltage of 100 V for a step-up transformer having 90% efficiency, find the output power and the voltage in the secondary if the output current is 3 A.

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Exam:

Class 12th Board 2017

Text solutionVerified

(a) Working principle: It worked on the principle of mutual induction. Whenever current in one coil changes an emf gets induced in the neighboring coil.
Voltage across secondary.

V_{s} = e_{s} = - N_{s} \frac{d ϕ}{d t}

Voltage across primary

V_{p} = e_{p} = - N_{p} \frac{d ϕ}{d t} \frac{V _{s}}{V _{p}} = \frac{N _{s}}{N _{p}} (here N_{s} > N_{p})

In an Ideal transformer
Power Input

=

Power Input

I_{p} V_{p} = I_{s} V_{s} \frac{V _{s}}{V _{p}} = \frac{I _{p}}{I _{s}} ∴ \frac{V _{s}}{V _{p}} = \frac{N _{s}}{N _{p}} = \frac{I _{p}}{I _{s}}

(b) Input power,

P_{i} = I_{i} \cdot V_{i} = 15 \times 100

= 1500 W

Power output,

P_{0} = P_{i} \times \frac{90}{100} = 1350 W

\Rightarrow I_{0} V_{0} = 1350 W

Output voltage,

V_{0} = \frac{1350}{3} V = 450 V

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(a) Describe, with the help of a suitable diagram, the working principle of a step-up transformer. Obtain the relation between input and output voltages in terms of the number of turns of primary and secondary windings and the currents in the input and output circuits.
(b) Given the input current 15 A and the input voltage of 100 V for a step-up transformer having 90% efficiency, find the output power and the voltage in the secondary if the output current is 3 A.

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Question Text	(a) Describe, with the help of a suitable diagram, the working principle of a step-up transformer. Obtain the relation between input and output voltages in terms of the number of turns of primary and secondary windings and the currents in the input and output circuits. (b) Given the input current 15 A and the input voltage of 100 V for a step-up transformer having 90% efficiency, find the output power and the voltage in the secondary if the output current is 3 A.
Topic	Alternating Current
Subject	Physics
Class	Class 12
Answer Type	Text solution:1
Upvotes	140

Text solutionVerified

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