Question

In post office box experiment Q/P=1/10. In R if 142 Omega is used then we get deflection towards righ and if R=143 Omega, then deflection is towards left. What is the range of unknown resistance?

Answer 1

Given :

In post office box experiment $\dfrac{Q}{P}$  =  $\dfrac{1}{10}$

The value of R for right deflection = 142 ohm

The value of R for left deflection  = 143 ohm

To Find :

The range of unknown resistance

Solution :

Let The unknown resistance = X

So, The range of unknown resistance is given as

            $\dfrac{X}{R}$ =  $\dfrac{Q}{P}$

∵     $\dfrac{Q}{P}$ = $\dfrac{1}{10}$

So,   $\dfrac{X}{R}$  = $\dfrac{1}{10}$

i.e ,   X  =  $\dfrac{R}{10}$

Now,

For For R = 142 $\Omega$  

       X  =  $\dfrac{142}{10}$      =   14.2 $\Omega$

And , For R = 143 $\Omega$

      X  =  $\dfrac{143}{10}$      =   14.3 $\Omega$

So, The range of X = (   14.2 $\Omega$ to 14.3 $\Omega$  )

Hence, he range of unknown resistance lies between  ( 14.2 $\Omega$ to 14.3 $\Omega$  )   Answer