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I'm doing some questions in my book and have hit a problem area.

#1) How would you change the resistance of a voltmeter to allow the voltmeter to measure a larger potential difference?

I was thinking that you would have to increase the resistance is order to measure a larger potential difference but I am not quite sure.

#2) How would you change the shunt in an ammeter to allow the ammerter to measure a larger current?

For this one I don't even know what a shunt is, my textbook hasn't really dealt with it at all. I'm not really sure what to say about it.

#3) An ohmmeter is made by connecting a 6.0V battery in series with an adjustable resistor and an ideal ammeter. The ammeter deflects full scale witha current of 1.0mA. The two leads are touched together and the resistance is adjusted so 1.0mA current flows.

a) What is the resistance of the adjustable resistor?

V/I = R 6.0V/1x10^-3A = 6000 ohms

b) The leads are now connected to an unknown resistance. What external resistance would produce a reading of 0.50 mA, half full scale?

The answer is also 6000 ohms but I'm not sure why

c) What external resistance would produce a reading of 0.25 mA, quarter scale?

The answer is 18000 ohms but I'm not sure why

d) What external resistance would produce a reading of 0.75mA, three quarter full scale?

The answer is 2000 ohms but once again I am not sure why.

I'm sure that these questions are absolutely stupid, but I really can't get my mind around them. I've done all the hard ones without a problem now I get to these and I'm stuck Any help you can give I would really appreciate! Thanks!

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