The power consumption of an electrical device varies directly with the square of the voltage applied. If a device consumes 150 watts when the voltage is 120 volts, how much power (in watts) will it consume at 240 volts?

Correct option is D

Given:
Power consumed, P₁ = 150 watts at voltage, V₁ = 120 volts
Voltage changes to V₂ = 240 volts
Power consumed at V₂ = P₂ (to be found)
Power varies directly with the square of voltage
Formula Used:
Since power varies directly with the square of voltage,
​$$P \propto V^2 \implies \frac{P_1}{P_2} = \frac{V_1^2}{V_2^2}$$​​
Or,
​$$P_2 = P_1 \times \left(\frac{V_2}{V_1}\right)^2$$​​
Solution:
 $$P_2 = 150 \times \left(\frac{240}{120}\right)^2 = 150 \times (2)^2 = 150 \times 4 = 600 \text{ watts}$$​​
The device will consume 600 watts at 240 volts.