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# Can anybody help me in this question in A2 phy red book by miles hudson watch

1. It is page 59 Q 3 b
2. Since current is decreasing according to the graph, using V=IR states that voltage will also decrease. Once the voltage drops bellow 4v the hand dryer will no longer work. Use the known values of V0 (6v, initial voltage) and V (4v, final voltage) in the discharge equation

V = V0e^-(t/RC).

This will give the answer in seconds. Hope this helps.

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3. Apologies, it asks to use the graph. V= IR , 4 = I x 200 therefor I = 0.02. Use the graphs line of best fit which gives approx 8 seconds.

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4. (Original post by x11chickling)
Since current is decreasing according to the graph, using V=IR states that voltage will also decrease. Once the voltage drops bellow 4v the hand dryer will no longer work. Use the known values of V0 (6v, initial voltage) and V (4v, final voltage) in the discharge equation

V = V0e^-(t/RC).

This will give the answer in seconds. Hope this helps.

Posted from TSR Mobile
but why is this wrong ? (I know it asks for a graph but theoretically i mean)
5. (Original post by x11chickling)
Apologies, it asks to use the graph. V= IR , 4 = I x 200 therefor I = 0.02. Use the graphs line of best fit which gives approx 8 seconds.

Posted from TSR Mobile
I did that but the answer is in the range of 50 to 55 so you'll have to deduct 60 from 8 you have any idea why?
6. Dont think it is unless ive messed mytheory up, but it gives the same answer as interpretation. Although, as you actually sub in T = RC as you value for RC as your given a time constant. The answer actually comes out as about 8.1s. So your using V = V0e^-(t/T). But non the less, I over complicated it with that method as it wanted you to interpret the graph. Apologies.

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7. The books answer is from 50-55 :O ? seems strange considering the math behind it.

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