Q#2 (Past Exam Paper – November 2012 Paper 12 Q6)
Variables x and y are related by the equation y = p – qx where p and q are constants.
Values of x and y are measured experimentally. The results contain a systematic error.
Which graph best represents these results?
Solution:
Answer: A.
Equation: y = p – qx
Comparing with the equation of a line y = mx + c, the gradient is negative and constant (m = -q). So, it is a straight line. [C and D incorrect]
Systematic error is due to the instrument, so all points should lie on the line as the error always occurs in the same direction.
From the equation, when x = 0, y = p, but due to systematic error, this value is reduced.
Choice A is correct as it shows no random error but a systematic error with the line not going through p.
Choice B shows random error without systematic error.
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