# Physics - Variable resistor limitations

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#1
Hi,
I was wondering how do I explain a variable resistor not being able to obtain the maximum or minimum voltage in a circuit. I will post a picture here
Last edited by Sclaremonths; 1 month ago
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1 month ago
#2
Do the earlier parts of the question tell you that the working voltage of the lamp is 12 V? I'm assuming that this is the case, so you want a circuit that can give any p.d. across the lamp from 0 V to 12 V.

Is it going to be possible to get the p.d. across the lamp down to 0 V? I know you could do this by opening the switch, but the idea would then be to increase the p.d. across the lamp from 0 V, so that wouldn't work. The closest you could get with this circuit would be when the variable resistor is set to its maximum value - would that be enough to stop the current in the circuit?

Similarly, is it going to be possible to get the p.d. across the lamp up to 12 V? The closes you could get with this cicuit would be when the variable resistor is set to its minimum value (i.e. zero) - would that be sufficent for there to be 12 V across the lamp?

Considering it's only two marks, there won't be a lot of detail required.
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#3
(Original post by Pangol)
Do the earlier parts of the question tell you that the working voltage of the lamp is 12 V? I'm assuming that this is the case, so you want a circuit that can give any p.d. across the lamp from 0 V to 12 V.

Is it going to be possible to get the p.d. across the lamp down to 0 V? I know you could do this by opening the switch, but the idea would then be to increase the p.d. across the lamp from 0 V, so that wouldn't work. The closest you could get with this circuit would be when the variable resistor is set to its maximum value - would that be enough to stop the current in the circuit?

Similarly, is it going to be possible to get the p.d. across the lamp up to 12 V? The closes you could get with this cicuit would be when the variable resistor is set to its minimum value (i.e. zero) - would that be sufficent for there to be 12 V across the lamp?

Considering it's only two marks, there won't be a lot of detail required.
okay thank you!
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