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Question

According to Joule's law of heating, heat produced in a resistor is expressed by which relation?

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RRB NTPC 2025 Graduate CBT 2 Question Paper PDF (10-Jul-2026) (Shift 1)
The correct answer is

H = I2Rt

Joule's law of heating states that when an electric current flows through a resistor, the heat generated depends on three factors: the square of the current, the resistance, and the time for which current flows.

Mathematically: \(H = I^2 R t\), where H is heat produced (in joules), I is current (in amperes), R is resistance (in ohms), and t is time (in seconds).

The relation H = Vt is incomplete — it omits resistance; H = V/I gives the resistance R (by Ohm's law), not heat; H = IR gives voltage V (by Ohm's law), not heat.

Hence, the correct expression for Joule's law of heating is H = I2Rt.

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