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Physics Question 27 – JEE-MAIN 2026

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In an experiment to determine the resistance of a given wire using Ohm's law, the voltmeter and ammeter readings are noted as 10 V and 5 A, respectively. The least counts of voltmeter and ammeter are 500 mV and 200 mA, respectively. The estimated error in the resistance measurement is _______ Ω

When physical quantities are measured, there's always some uncertainty. When these quantities are used in a formula to calculate another quantity, the uncertainties propagate.

Step 1: Calculate the nominal resistance✦ Active

Given voltmeter reading V=10 V and ammeter reading I=5 A. Using Ohm's law, the resistance R is:

R=VI=10 V5 A=2 Ω
Step 2: Determine the fractional error in resistance○ Expand

The least count of the voltmeter is ΔV=500 mV=0.5 V. The least count of the ammeter is ΔI=200 mA=0.2 A. For a quantity R=VI, the fractional error is given by:

ΔRR=ΔVV+ΔII

Substitute the values:

ΔRR=0.5 V10 V+0.2 A5 A=0.05+0.04=0.09
💡 Teacher's Secret Hint

Ensure units are consistent (V and A for readings, V and A for least counts) before calculation.

Step 3: Calculate the absolute error in resistance○ Expand

Now, calculate the absolute error ΔR:

ΔR=R×0.09=2 Ω×0.09=0.18 Ω
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