Q5-9702_w18_qp_11

2018 paper (oct/nov) component 11

A digital meter has an accuracy of $\pm$ 1%.

The meter is used to measure the current in an electrical circuit.

The reading on the meter varies between 3.04 A and 3.08 A. What is the value of the current, with its uncertainty?

Solution

The raw reading, when taken account of the fluctuation, has a value of (3.06+-0.02) A, because the current has a max value of 3.08 A and min value of 3.04 A, both is 0.02 A from 3.06.

Moreover, each value of reading has an meter accuracy of 1%. So 3.08 A *0.01=0.03 A of added uncertainty, and 3.04 A *0.01 also yield 0.03 A. So the new max value becomes (3.08+0.03)=3.11 A, the new min value becomes (3.04-0.03)=3.01 A. Now, the new uncertainty would be 3.11-3.06=3.06-3.01=0.05 A.