Physics 2007 JAMB Past Questions - Question 18: A 120 V, 60 W 51 amp is to be operated on 220 V a.c. supply mains. Calculate the value of non-inductive resistance that would be required :c ensure that the lamp is run on correct value.

Correct Answer

C

Explanation

To operate a 120 V, 60 W, 0.51 A lamp on a 220 V AC supply while maintaining the same power (60 W), you need to find the value of non-inductive resistance required.

The power consumed by the lamp can be calculated using the formula:

Power (P) = Voltage (V) × Current (I)

Given the original power is 60 W and the original voltage is 120 V, you can find the original current:

I = P / V
I = 60 W / 120 V
I = 0.5 A

So, the original lamp operates at 0.5 A.

Now, you want to operate it at 220 V. To calculate the resistance needed, you can use Ohm's law:

Resistance (R) = Voltage (V) / Current (I)

For the new voltage (220 V) and the original current (0.5 A), you can calculate the resistance:

R = 220 V / 0.5 A
R = 440 ohms

So, to ensure the lamp operates correctly on a 220 V AC supply while maintaining its original power, you would need a non-inductive resistance of 440 ohms.