A power transmission line feeds input power at 2300 V to a step-down transformer with its primary windings having 4000 turns. What should be the number of turns in the secondary in order to get output power at 230 V ?

Given, Input voltage, V 1 = 2300 V Output voltage, V 2 = 230 V No. of turns in the primary coil, n 1 = 4000 Using the formula for transformers, we get V 2 V 1 = n 2 n 1 Or, n 2 = n 1 × V 2 V 1 = 4000 × 230 2300 = 400 t u r n s

Write the relation between root mean square value and peak value of alternating current.

The relationship between the peak and the rms value of current in an a.c. circuit is I r m s = I 0 2 where, I o is the peak value of alternating current.

What is the principle of working of a transformer? Write any one reason for energy loss in transformer.

Transformer works on the principle of mutual induction. A changing alternate current in primary coil produces a changing magnetic field, which induces a changing alternating current in secondary coil. Energy losses in transformer: Flux leakage due to poor structure of the core and air gaps in the core.

A step-down transformer converts 2200 Volt transmission line voltage to 220 Volts. Number of turns in secondary coil are 500 . Evaluate the number of turns in primary coil.

V S = Ns*Vp/Np Where, V p = Primary voltage, V s = Secondary voltage, N p = number of turns in the primary N s = Number of turns in the secondary Np=Ns*Vp/Vs Np= 2200 × 500 220 = 5000 The number of turns in primary coil 5000

Write an expression for the impedances of a LCR-series circuit. In which condition these impedances is minimum?

Impedance of a LCR circuit is given by, Z = R 2 + X L - X C 2 Where, R is the resistance XL is the inductive resonance XC is the capacitive resonance The impedance of a series LCR circuit is given by will be minimum when ωL=1/ωC, i.e., when the circuit is under resonance. Hence, for this condition, Z will be minimum and will be equal to R.

E M B I B E

EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR PHYSICS>Chapter 7 - Alternating Current>Uttarakhand Board-2020>Q 8

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12th Uttarakhand Board

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What is meant by Wattless current? Clarify.

Important Questions on Alternating Current

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12th Uttarakhand Board

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EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR PHYSICS>Chapter 7 - Alternating Current>Uttarakhand Board-2020>Q 9

A light bulb and an open coil inductor are connected to an ac source through a key as shown in figure. The switch is closed and after sometime, an iron rod is inserted into the interior of the inductor. What will be effect on glow of light bulb while inserting the rod. Give your answer with reason.

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