Powering Earth

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Question 28
Medium

This question is about how electricity is transferred in power networks.

a.

State:

  1. What a step-up transformer does to the potential difference.
  2. The primary reason for using a step-up transformer immediately after a power station generator before long-distance transmission.
[2]
b.

The table below shows information for a transmission-line step-up transformer:

QuantityValue
Potential difference across primary coil (VpV_pVp​)24 000 V24\,000\text{ V}24000 V
Current in primary coil (IpI_pIp​)8000 A8000\text{ A}8000 A
Potential difference across secondary coil (VsV_sVs​)400 000 V400\,000\text{ V}400000 V

Assuming the transformer is 100%100\%100% efficient, calculate the current in the secondary coil (IsI_sIs​) of the transformer.

[2]
c.

An oscilloscope is connected across the output of a large AC generator at a power plant. The trace on the screen shows a wave that continuously alternates between positive and negative peaks.

  1. Identify the type of current supplied by this generator.
  2. Explain how this trace on the oscilloscope indicates that this is not a direct current (d.c.) supply.
[2]

Powering Earth Questions

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