Question

(a) Write Joule’s law of heating.
(b) Two lamps, one rated 100 W; 220 V, and the other 60 W; 220 V, are connected in parallel to electric mains supply. Find the current drawn by two bulbs from the line, if the supply voltage is 220 V.

Answer 1

Answer:

a) Joule's law of heating can be defined as:  when current passes through a conductor, heat is generated.  It is also known as Ohmic heating or resistive heating.

P = I² R = V²/R

Where, P is in watts, I is in Amperes, R is in ohms and V is volts.

b) firstly we would find the resistance of the lamps.

P₁ = 100 W

V₁ = 220 V

R ₁ = V₁²/P₁ = 484 Ω

P₂ = 60 W

V₂ = 220 V

R₂ = V₂²/P₂ = 806.67 Ω

The lamps are connected in parallel. Equivalent resistance =

R = (R₁×R₂)/(R₁+R₂) = (484 Ω×806.67 Ω)( 484 Ω+806.67 Ω) = 302.5 Ω

From Ohm's law, current drawn is given by:

I = V /R = 220 V/ 302.5Ω = 0.727 A

Answer 2

Answer:

The answer is given in the attachment.

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