A student wants to determine the true emf of a dry cell using a digital voltmeter of…
PHYSICS · Subjective · CBSE · Physics · Units and Measurements · Units and Measurements
Problem
A student wants to determine the true emf of a dry cell using a digital voltmeter of range 0–10 V and a milliammeter. The voltmeter has a constant positive zero error of +0.05 V, while the milliammeter occasionally shows small fluctuations of ±0.5 mA around its mean reading.
The following measurements are recorded:
Open-circuit voltmeter reading = 1.63 V
Current through a known resistance of 10.0 Ω connected across the cell = 165 mA (average of 10 readings)
Answer the questions that follow:
(a) Classify the error due to the zero shift of the voltmeter and the fluctuations of the milliammeter, giving justification for each classification.
(b) Calculate the best estimate of the internal resistance of the cell using the given data.
(c) Using your result in (b), compute the percentage error introduced in the emf because of the voltmeter’s zero error.
(d) Which of the two error sources in this experiment is more significant for the final value of emf? Give a quantitative or logical reason for your choice.