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A question about relay

  1. Feb 4, 2015 #1
    [PLAIN]http://[url=http://postimg.org/image/pwudznwxd/][PLAIN]http://s16.postimg.org/pwudznwxd/image.jpg [Broken] [Broken] Hello everyone,

    I'm new to this forum. I'm glad that there is a forum for physics as there are questions that I try to solve but to no avail , I hope to find the answer here.
    I study IGCSE and yesterday I was doing a past paper exam and I couldn't agree with the answer in the mark scheme of one of the questions.

    I know that the function of the relay is to switch on a circuit with powerful current using a circuit with small power , which is safer. But in the answer I found the function of the relay is very different from what I know. I attached the question and the answer.

    I hope I can find an explanation here.

    Thank you all very much in advance.

    Last edited by a moderator: May 7, 2017
  2. jcsd
  3. Feb 4, 2015 #2


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    All I see for your links or images or whatever they are is a broken-link symbol
  4. Feb 4, 2015 #3
    Sorry, it's my first time to upload an image using a host site.

  5. Feb 4, 2015 #4


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    2017 Award

    Hi there
    Welcome to PF :)

    since you have told us noting else about the circuit
    voltages, lamp type its requirements etc

    and you appear to be using TTL or CMOS gates/triggers that means their outputs are VERY limited in the amount of current they can supply
    So they will switch a relay which in turn will switch the higher current requires by the lamp

  6. Feb 5, 2015 #5
    Ok great I understand now. Thank you very much for explaining it to me.
  7. Feb 5, 2015 #6


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    2017 Award

    Relays are also used to switch high voltages (not just high currents), btw.
    The Mark Scheme answer is spot on.
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