Calculating Equivalent Resistance and Number of Light Bulbs in a Series Circuit

6. Several Light Bulbs Connected in Series

Several light bulbs are connected in series across a 115 V source of EMF.

a. Equivalent Resistance Calculation

Question: What is the equivalent resistance if the current in the circuit is 1.70 A?

Explanation:

a) I = V / R

1.70 = 115 / R

R = 115 / 1.70

R = 67.647

R = 67.65 ohms

Therefore, equivalent resistance is 67.65 ohms

b. Number of Light Bulbs Calculation

Question: If each light bulb has a resistance of 1.50 ohms, how many light bulbs are in the circuit?

Equivalent resistance of circuit from above sum is 67.65 ohms

Given resistance of each bulb is 1.50 ohms

Number of light bulbs = Equivalent resistance / Resistance of each bulb

= 67.65 / 1.50

= 45