How to Calculate Resistance, Current, and Effective Resistance in a Series Circuit

13 May 2022

Given the data of two lamps rated 60W; 240V and 100W, 240V respectively connected in series to a 240V power source:

a) What is the resistance of each lamp?

b) What is the effective resistance of the circuit?

c) How much current is passing through the lamps?

See the answers below.

The total power of the circuit is equal to the sum of the powers of each lamp.

P = 60 + 100 = 160W

Now, with a voltage source of 240V, we can find the current in the circuit using the formula P = V * I.

I = P / V = 160 / 240 = 0.67 amp

Therefore, the answer for c) is 0.67 amp

Using Ohm's law, we can find the resistance of each lamp.

a) For the 60W lamp:

R = V^2 / P = 240^2 / 60 = 133.33 ohms

b) For the 100W lamp:

R = V^2 / P = 240^2 / 100 = 225 ohms

To find the effective resistance of the circuit in series, we sum the resistances:

Effective resistance = 133.33 + 225 = 358.33 ohms