A laboratory power supply delivers a constant potential difference to a purely…
PHYSICS · Multi-part · CBSE · Physics · Current Electricity · Current Electricity
Problem
A laboratory power supply delivers a constant potential difference V0=120V to a purely resistive load. You are asked to design a resistor that will safely dissipate thermal energy under varying line conditions.
(a) Starting from fundamental relationships among electrical quantities, derive an algebraic expression for the power P dissipated in a resistor of resistance R connected across the supply in terms of V0 and R.
(b) Using your expression from part (a), determine the resistance that will cause the resistor to dissipate exactly 25W when the supply is at its nominal value of 120V.
(c) In actual operation the supply voltage may vary by ±5% of its nominal value. For the resistance found in part (b), calculate the maximum power that could be dissipated due to this voltage variation.
(d) Commercial power resistors are often specified to handle 1.5 times their nominal power rating without damage. Evaluate whether a resistor rated at 25W is adequate for this application, providing quantitative justification.