Reading with Uncertainty

lundi 29 juillet 2013

1. The problem statement, all variables and given/known data

The manufacturer of a digital ammeter quotes its uncertainty as ±1.5% ±2 digits.

a. Determine the uncertainty in a constant reading of 2.64 A

b. The meter is used to measure the current from a d.c. power supply. The current is found to fluctuate randomly between 1.58 A and 2.04 A. Determine the most likely value of the current, with its uncertainty

2. Relevant equations

Not sure

3. The attempt at a solution

The answer of (a) is ±0.06 A and (b) is (2.01 ± 0.09) A

I am not sure what ± 2 digits means. Is it ± 0.02 ?

My attempts:

(a) uncertainty = 2.64 x 1.5 % + 0.02 = 0.0596 ≈ 0.06 A

(b)

Average = (1.58 + 2.04) / 2 = 1.81 A

Uncertainty for 1.58 A = 1.58 x 1.5% + 0.02 = 0.0437 ≈ 0.04 A

Uncertainty for 2.04 A = 2.04 x 1.5% + 0.02 = 0.0506 ≈ 0.05 A

Total uncertainty = 0.04 + 0.05 = 0.09 A

Then stuck....

Thanks