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Old 14th September 2005, 07:34 PM   #1
dome406 is offline dome406  United Kingdom
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Join Date: Mar 2004
Location: uk
Question Help

I have just started A-level electronics and am slightly confused at this question, I know it is very simple but it is not explained in my textbook, hope you dont mind me asking. How would you calculate it.

Calculate the maximum safe current through a resistor of:
a) 100Ohm 1W

Thanks very much.
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Old 14th September 2005, 09:10 PM   #2
Geoff is offline Geoff  United Kingdom
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Join Date: Apr 2001
Location: UK
W = V x I

Ohms Law: V = I x R

so W = (I x R) x I = I^2 x R

or I = sqrt(W / R)

so I = sqrt(1 / 100) = 0.1A

The theoretical maximum current is therefore 0.1A but in practice you would never run a component anywhere near to its maximum rating (which could be specified at a temperature rise of up to 70C). Realistically, you would limit the current through this resistor to 50mA or less.
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Old 14th September 2005, 09:21 PM   #3
dome406 is offline dome406  United Kingdom
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Join Date: Mar 2004
Location: uk
Thanks very much
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