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# Phys prac

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Hey.. was wondering if anyone could help me with my phys prac i'm not exactly sure on what to do

here goes: when a lamp is dissipating a greater power the temperature increases and hence the resistance of the filament changes. you are to investigate how the power P dissipated by the filament of a lamp varies with the resistance R of the filament.. we were giving a pic of a circuit but i cant draw that in here.. hehe

is it just V=IR and P=IV and stuff i like i have to investigate

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Hello

You would place an ammeter in series (anywhere) to measure the current of the circuit. Then connect a volmeter across your filament lamp to measure the voltage. The power dissiapated across it the lamp would be P = VI and its resistance would be R = V/I. I'm not too sure how to change the resistance of the filament lamp, i'm pretty sure its temperature would rise way too fast for you to measure any change in resistance. I think replacing the filament lamp with a variable resistor would work. This way, you can easily have differing values of resistance and you can calculate it easily from the voltage and current readings.

After you calculate the values for the resistance and its corresponding power, plot that on a graph. Power on y-axis and resistance on x-axis. Since the relationship between resistance and power is P = I^2*R, the gradient of the graph u plot should equal to the current squared.

Michael

Disclaimer: I'm not really sure what i describe above would accomplish what you asked. I'd really appreciate if someone with more knowledge about phsyics could check it and tell me if i'm wrong. Should I be changing the power supply instead of the resistance of the "lamp"?

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Thanks a lot michael

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Np, tell me if it worked!