I have this circuits question that i've tried to do, but i'm not sure about my answers and i'm sure i'm going wrong somewhere...(adsbygoogle = window.adsbygoogle || []).push({});

The 4.00 V cell in the circuits below has zero internal resistance. An accurately calibrated voltmeter across XY reads 1.50 V

http://home.ripway.com/2005-7/361234/circiut.bmp

a) Calculate the resistance of the voltmeter.

i did this :

Vyz = 1.5 V

therefore Vxy=4.00-1.50=2.50V

Ixy=Vxy/Rxy

=2.5/60

=0.041666666...

therefore Is=0.041666... (supply current)

I(40 ohm resistor)=V(40 ohm resistor)/R(40 ohm resistor)

=1.5/40

=0.0375

therefore Ivoltmeter=0.041666...-0.0375

=0.00416666...

1/Req=1/40 + 1/R(voltmeter)

=(Rv+40)/40Rv

Req=40Rv/(Rv=40)

Vs=Is x R(total)

R(total)=60+ ( 40Rv/(Rv+40) )

4.00=0.04166666... x 60+ ( 40Rv/(Rv+40) )

96=60+ ( 40Rv/(Rv+40) )

36=40Rv/(Rv+40)

36Rv+1440=40Rv

4Rv=1440

Rv=360

Voltmeter resistance=360 Ohms

This seem way too low for a decent voltmeter, so i think it's wrong, but i can't see how!!

and for part b): Calculate the voltmeter reading when it is connected across Y'Z'

I did this:

1/Req=1/400 + 1/360

=19/3600

Req=189.473...

R(total)=189.473...+600

=789.473...

Is=Vs/R(total)

=0.0050666...

V(600 ohm resistor)=Is x R(600 ohm resistor)

=3.04V

V(400 ohm resistor)=Vs - V(600 ohm resistor)

=o.96

Voltmeter reads 0.960V

this seems so wrong!!

i have no idea!!

please help

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# Homework Help: Circuits problem

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