Question

Two lamps, one rated 100W at 220V and the other 60W at 220V, are
connected parallel. What current is drawn from the supply?​

Answer 1

Answer:

Lamp 1

P = 100W , V= 220 V , I = ?

I = P/V

I = 100/220

I (1)= 0.45 A

Lamp 2

P = 60W , V = 220V , I = ?

I = P/V

I = 60/220

I (2)= 0.27 A

I(P) = I(1) + I(2)

= 0.45 + 0.27

I(P) = 0.72 A

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Answer 2

There are two cases in this question. In the first case power of lamp is 100W and voltage is 220V. Whereas in second case, power is 60W and voltage is 220V.

Both the lamps are connected in parallel.

We have to find the current drawn from the supply.

Now,

R = V²/P

For FIRST CASE:

R1 = (220)²/100

R1 = 484 ohm

For SECOND CASE:

R2 = (220)²/60

R2 = 806.6 ohm

As, both the lamps are connected in parallel. So,

1/Rp = 1/R1 + 1/R2

1/Rp = (R2 + R1)/R1R2

Rp = R1R2/(R2 + R1)

Substitute the values of R1 and R2

→ Rp = (484 × 806.6)/(806.6 + 484)

→ Rp = 390394.4/1290.6

→ Rp = 302.5 ohm

Total resistance is 302.5 ohm and voltage is 220V. So,

From ohm's law,

V = IR

→ 220 = I × 302.5

→ 220/302.5 = I

→ 0.73 = I

Therefore, the current drawn from the supply is 0.73A.