Question

Two lamps 1 rated 100 watt at 220v and other 200 watt at 220v are connected then find the current drawn in series and in parallel

Answer 1

HI !

Power = P = 100 W
Voltage = V = 220v
Resistance = R

P = V²/R
100 = 220 ×220/R
R = 220 × 220/100
= 484 Ω
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Power = P = 60 W
Voltage = V = 220v
Resistance = R

P = V²/R
60 = 220 × 220/R
R = 220× 220/60
= 806.7 Ω
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As the resistors are connected in parallel ,
total resistance = 1/R

1/R = 1/484 + 1/806.7
= 806.7 + 484/484×806.7
= 1290.7/390442.8
R = 390442.8/ 1290.7 = 302.5 ohms

Total resistance = 302.5 Ω


I = current

V = IR
220 = I × 302.5

I = 220/302.5
= 0.73 A

The current drawn is 0.73 A

Answer 2

Answer:

I_series = 0.30 A

I_parallel = 1.36 A

Explanation:

Given :

Two lamps power as 100 W and 200 W at 220 V.

We have resistance formula :

R₁ = 220 × 220 / 100 = 484 Ω

R₂ = 220 × 220 / 200 = 242 Ω

In series combination :

R_net = 484 + 242 Ω

= > 726 Ω

We have ohm's law :

V = I R

I = 220 / 726 A

I = 0.30 A

( ii ) In parallel combination :

1 / R_net = 1 / 484 + 1 / 242 Ω

R_net = 484 / 3 Ω

Given :  V = 220 V

I' = 220 / 484 × 3 A

I' = 1.36 A