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March 29, 2024, 11:23:28 pm

Author Topic: Need help with a question  (Read 635 times)  Share 

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Samueliscool223

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Need help with a question
« on: February 14, 2020, 10:17:01 pm »
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A projector lamp is designed to take a current of 4.0A when used with a 32V home lighting unit, what resistance ought to be placed in series with the lamp if it is to be used on a 240V supply?



The answer is 52 ohms, how do you get it? I thought you'd have to derive the resistance by using i=v/r ... 4=240/r
r=60, but i guess not. Please help

sweetiepi

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Re: Need help with a question
« Reply #1 on: February 14, 2020, 10:40:34 pm »
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A projector lamp is designed to take a current of 4.0A when used with a 32V home lighting unit, what resistance ought to be placed in series with the lamp if it is to be used on a 240V supply?



The answer is 52 ohms, how do you get it? I thought you'd have to derive the resistance by using i=v/r ... 4=240/r
r=60, but i guess not. Please help
Hey!
The whole circuit will use 240V. The lighting uses 32V. This leaves 208V for the resistor.

Assuming this circuit is in series, the current for both the light and the resistor must be the same.

\(\therefore R=\frac{V}{I}\) = \(R = \frac{208V}{4.0 A}\)
\(\therefore R = 52 \Omega\)

Hope this helps! :)
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Samueliscool223

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Re: Need help with a question
« Reply #2 on: February 14, 2020, 10:51:06 pm »
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Hey!
The whole circuit will use 240V. The lighting uses 32V. This leaves 208V for the resistor.

Assuming this circuit is in series, the current for both the light and the resistor must be the same.

\(\therefore R=\frac{V}{I}\) = \(R = \frac{208V}{4.0 A}\)
\(\therefore R = 52 \Omega\)

Hope this helps! :)
Ok I get it now, I think I mustve read the question wrong, haha. Thanks