A potentiometer wire has length 4 m and resistance 8 ohm. The resistance that must be connected in series with the wire and an accumulator of e.m.f. 2V, so as to get a potential gradient 1 mV per cm on the wire is:

  • Option 1)

    44 ohm

  • Option 2)

    48 ohm

  • Option 3)

    32  ohm

  • Option 4)

    40  ohm

 

Answers (1)

As we learnt in

Potential gradient -

V=iR= left (frac{e}{R+R_{n}+r} 
ight )R

x=frac{V}{L}=frac{e}{(R+R_{n}+r)}frac{R}{L}

- wherein

r- internal resistance

 

 

 

Potential \:gradient=\frac{dv}{dr}=1mV/cm

So for 400 cm \Delta V=\frac{V}{R+Rs}\times R

\\0.4=\frac{2}{8+R}\times 8

=8+R=\frac{16}{0.4}=40

R=32\ ohm


Option 1)

44 ohm

Incorrect

Option 2)

48 ohm

Incorrect

Option 3)

32  ohm

Correct

Option 4)

40  ohm

Incorrect

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