Question

What is a potential meter explain its principal
(a)Explain how it can be used to compare the emf of two cells
(b)Explain how it can be used to determine the internal resistance of a cells.

Answer 1

Potentiometer

It is a three terminal resistor with a sliding or rotating contact that format an adjustable voltage devider

(a) compare Emf of two cells

Ref. image 1

Ref. image 2

$E_k=i\left(\rho l_1\right)E_u=i\left(\rho l_2\right)$

$\rho =$ Resistance of wire ab per unit length

$\frac{E_k}{E_u}=\frac{l_1}{l_2}$

(b) Determine internal resistance

ref. image 3

$i=\frac{E}{R+r}$ __(I)

$V=E-ir=iR$ ___(II)

From eq (I) and (II)

$r=R(\frac{E}{V}-1)$