Homework Help: ap physics

Posted by ash on Thursday, October 25, 2007 at 11:22pm.

can you please check my answers and help me with one question?

During a lie dector test, a voltage of 6 V is impressed across two fingers. When a certain question is asked, the resistance between the fingers drops from 400,000 ohms to 200, 000 ohms. What is the current (a) initially through the fingers, and (b) when the resistance between them drops? (this question I dont understand)

How much resistance allows an impressed voltage of 6V to produce a current of 0.006 A ? I got 1000 ohm

What is the resistance of a clothes iron that draws a current of 12 A at 120 V? I got 10 ohm

The current in an incandescent lamp is 0.5A when connected to a 120-V circuit, and 0.2A when connected to a 10-V source. Does the resistance of the lamp change in these cases? Explain your answers and defend it with numerical values?( I got: 120 V/0.5A=240 ohms and 10V/0.2A=50 ohms. Yes the resistance changes in both cases.)

ap physics - drwls, Thursday, October 25, 2007 at 11:31pm
The current in the first problem is V/R in both cases. Just compute the numbers at bot values of R.

Your second answer is correct.
Your third answer is correct.
Yes, the resistance of the tungsten lamp filament increases quite a bit when it gets hotter (as it does with higher voltage operation).

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