1994 ce questions(urgent)

Zidane

2011-12-29 1:25 am

1. 100kW of of electrical power is transmitted at 20 kV through cables of total resistance 4 ohm. Find the potential drop and power loss in the cables.
ans: 20V and 100W

How to calculate the 2 ans? What is meant by 'transmitted at 20kV'? Does it mean that at the beginning of the cable the potential is 20kV, at the end of the cable it is 19980V(potential drop)?

2. 'The major energy change of a ticker-tape time is from electrical to mechanical.' Why is this statement correct? Can some1 describe the changes take place?

thanks

更新1:

another question: In which parts of a ticker-tape timer make use of electromagnet?

回答 (1)

天同

2011-12-29 3:54 am

✔ 最佳答案

1. Current through the cable = 100,000/20,000 A = 5 A
Hence, potential drop = 5 x 4 v = 20 v

Power loss = 5^2 x 4 w = 100 w

You interpretation is right.

2. The reason is apparent. Electrical signal is fed into the ticker-timer to cause the "ticker" to vibrate at a pre-set period. The vibration is a mechanical movement.

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