Show how would you join three resistors, each of
resistance 9 12 so that the equivalent resistance of
the combination is (a) 13.5 S2 (b) 6 12?
OR
(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.
Please say the right and complete answer
Answers
Explanation:
For equivalent resistance to be 13.5 ohms---
we will connect two resistances in parallel and one in series
Verification--
R (series) = 9
1/R (parallel) = 1/9 + 1/9
1/R = 2/9
R = 9/2
R = 4.5 ohms
Total resistance = R(series) + R(parallel)
= 9 + 4.5
= 13.5 ohms
For equivalent resistance to be 6 ohms---
we will connect two resistances in series and one in parallel
Verification--
R(series) = 9 + 9
R(series) = 18 ohms
1/R(parallel) = 1/18 + 1/9
1/R(parallel) = 1+2/18
R = 18/3
R. = 6 ohms
Answer:
Explanation:
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