Question

A 30V-90W lamp is operated on a 120V DC line. A resistor is connected in series with the lamp in order to glow it properly. The value of resistance

• A. 10 \(\Omega\)
• B. 30 \(\Omega\)
• C. 20 \(\Omega\)
• D. 40 \(\Omega\)

Hint:

Use the formula \( P = \frac{V^2}{R} \) to determine the resistance needed for devices working at a specific power.

Answer 1

The Correct Option is C

Using the power formula \( P = \frac{V^2}{R} \), we calculate the required resistance for the lamp to operate at its specified power. The total resistance needed is found to be 20 \(\Omega\).