Question

The emf of a cell is 12 volt in a closed curcit having a resistance of 10 ohm it sends a current of 1 ampere find the internal resistance of a cell

Answer 1

Explanation:

Emf is the work done by the cell to carry a unit charge through the closed circuit. So, it is the sum of the work done to carry the charge through the conducting wire with external resistance(R) and cell with internal resistance (r).

ℰ = V+V’ ——————–(1)

By Ohms Law

V=IR ———— (2)

V’ =Ir ————–(3)

From equation (2) and (3)

ℰ = IR + Ir

v = I (r + R)

I=ℰ /(R+r) ———————(4)

Substituting (4) in (2)

V= IR = (Rℰ)/(R+r)

Now, from equation (1)

V= ℰ – V’

= ℰ – Ir

Ir = ℰ – V

r = (ℰ -V) / I

putting I=V/R

r =(ℰ -V)R / I

so V=IR=1x10=10V

r=(12-10)10/1

r=2x10

r=20ohm