Solving a Question on Relay with IGCSE Physics

• Syndy

Syndy

[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.

[PLAIN]http://[url=http://postimg.org/image/pwudznwxd/][ATTACH=full]199660[/ATTACH]

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Sorry, it's my first time to upload an image using a host site.

imgurl

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

Dave

Ok great I understand now. Thank you very much for explaining it to me.

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