Question 10
The resistance R of a resistor is
to be determined. The current I in the resistor and the potential
difference V across it are
measured.
The results, with their
uncertainties, are
I = (2.0 ± 0.2) A V = (15.0 ± 0.5) V.
The value of R is calculated to
be 7.5 Ω.
What is the uncertainty in this value
for R ?
A ± 0.3 Ω B ± 0.5 Ω C ± 0.7 Ω D ± 1 Ω
Reference: Past Exam Paper – November 2014 Paper 13 Q5
Solution:
Answer:
D.
Ohm’s law: V = IR
R = V / I = 15.0 / 2.0 =
7.5 Ω
ΔR / R = ΔV/V + ΔI/I
ΔR / 7.5 = 0.5/15 + 0.2/2
ΔR = (0.5/15 + 0.2/2) × 7.5 = ± 1
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