Question

a)An electric bulb is labelled at 100W-220V. The bulb is connected to a supply of 120V.
Calculate heat produced by the bulb in 2 minutes. (3)
b)State Joule's law of heating. (1)
c) Define the SI unit of potential difference. (1)​

Answer 1

Answer: (i)

given - P= 100w

And V = 220v

So We know P = V^2/R

Therefore R= V^2/P

= 220x220/100

=484ohm

Now V= 120v

t= 2min

360sec

H= I^2Rt

H=120(I X R = V) X V/R X 360

= 120x 0.24X360

= 10368JOULES /SEC

HENCE HEAT PRODUCED IS 10368J/S

(ii)Joules law of heating states that the heat produced when electricity grows through a circuit is directly proportional to the square of current flowing through it , resistance of the object and the time till which current flows.

(iii) SI unit of potential difference is defined as the 1joule of work done to move and 1coulomb of charge from one point to another .

That is V= W/Q