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anonymous

  • 5 years ago

A relay is required to operate 800 m from its power supply. The power supply has negligible internal resistance. The relay requires 16.0 V and a current of 0.60 A to operate. A cable connects the relay to the power supply and two of the wires in the cable are used to supply power to the relay. The resistance of each of these wires is 0.0050 Ω per metre. What is the minimum output e.m.f. of the power supply? A 16.6 V B 18.4 V C 20.8 V D 29.3 V

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  1. JamesJ
    • 5 years ago
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    So calculate how much cable you need and the resistance of that wire. From there, how much potential difference is lost over the wires. Hence what potential difference you need at the source in order to have the desired V at the relay.

  2. anonymous
    • 5 years ago
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    The Total resistance of the relay and the wires comes out to be; R=34.6ohms and the V will then be R=V/I Got it thanks :)

  3. anonymous
    • 5 years ago
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    so the answer is C

  4. JamesJ
    • 5 years ago
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    How did you find that value of R?

  5. anonymous
    • 5 years ago
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    Resistance of relay+resistance of wires (16V/0.6A)+ (0.005ohmsx800mx2)

  6. JamesJ
    • 5 years ago
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    Got it. Good.

  7. anonymous
    • 5 years ago
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    yeah, thanks for guiding

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