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## Homework Statement

The circuit shown is used to produce a current-voltage graph for a 12V, 24W lamp:

http://img338.imageshack.us/img338/9139/circuitlu6.jpg [Broken]

http://img338.imageshack.us/img338/9139/circuitlu6.jpg [Broken]

a) Calculate the resistance of the lamp in normal operation.

b) Calculate the value for R which wold enable the voltage across the lamp to be varied between 0V and 12V.

## Homework Equations

P = IV

V = IR

## The Attempt at a Solution

a) P=IV

24 = 12I

I = 2A

V = IR

12 = 2R

R = 6 Ohms

b) Absolutely no idea how to go about doing this... it seems that the voltage across the resistor R ought to be 8V, but I don't know, since we haven't been told what the component with the arrow pointing into the 24 ohm resistor is...

Thanks for your help.

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