ELECTROMAGNETISM

Numerical No:    15.1   15.2   15.3   15.4   15.5   15.6   15.7

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NUMERICAL NO: 15.1

A transformer is needed to covert a mains 240 V supply into a 12 V supply. If there are 2000 turns on the primary coil, then find the numbers of turns on the secondary coil.

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NUMERICAL NO: 15.2

A step-up transformer has a turn ratios of 1:100. An Alternate supply of 20 V is connected across the primary coil. What is secondary voltage?

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NUMERICAL NO: 15.3

step-down transformer has a turn's ratio of 1:100. An ac voltage of amplitude 170 V is applied to the primary. If the current in the primary is 1.0 mA, what is the current in the secondary?

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NUMERICAL NO: 15.4

A transformer, designed to convert the voltage from 240 V a.c. mains to 12 V, has 4000 turns on the primary coil. How many turns should be on the secondary coil? If the transformer were 100% efficient, what current should flow through the primary coil when current in the primary coil was 0.4 A?

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NUMERICAL NO: 15.5

A power station generates 500 M W of electrical power which is fed to a transmission line. What current would flow in the transmission line if the input voltage is 250 kW?

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NUMERICAL NO: 15.6

The diagram shows a wind turbine which runs a 150 kW generated with an output voltage of 1000 V. the voltage is increased by transformer T₁ to 10000 V for transmission to a town 5 km away through power lines with a total resistance of 2 Ω. Another transformer T₂, at the town reduces the voltage to 250 V. Assume that the transformers are ideal. When the system is running at full power:
    a.    What is the current in the Power line?
    b.    What is the voltage drop and power lost along the power line? Also find the voltage at the input to the town transformer.

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NUMERICAL NO: 15.7

A step-up transformer has 80 turns on its primary coil and 1200 turns on its secondary coil. The primary circuit is supplied with an alternating current at 120 V.
    a.    What voltage is being applied across the secondary circuit?
    b.    The current in the secondary circuit 1s 2.0 A. What current is in the primary circuit?
    c.    What are the power input and output of the transformer?

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