Page 59 - Physics

Measurement

Parallax error When a measurement is taken
Parallax error occurs when an observer takes using an instrument with the
measurement from wrong positions. Consider Figure pointer below or above the
2.40. zero mark shown in Figure 2.41
(a) and (b), zero errors occur.
Position 2
Position 1 Position 3 To minimise zero error,
the instrument should be
adjusted to read zero, shown
in Figure 2.42. A pointer can be
adjusted to read zero.

Figure 2.40: Parallax error

Positions 1 and 3 will give higher and lower readings
than position 2. A reading taken at position 2 will Figure 2.42: Pointer at the zero
be correct because the observer has positioned his/ mark
her eyes directly above the mark to be read. Thus, to
minimize parallax error, the observers must position For example, in a vernier
their eyes directly above the mark to be read. calliper, zero error arises when
the zero mark on the main and
Zero error vernier scales do not coincide
For a measurement to be considered accurate, the with each other when the jaws
initial reading of a pointer should be at a zero mark. are closed. A micrometre screw
gauge may also have zero error
if the zero mark on the spindle
and sleeve do not coincide after
closing the gap between the
spindle and the anvil.

Instrumental error
An instrumental error is caused
by the instrument itself. The
(a) Pointer below (b) Pointer after error occurs because of defects
zero mark zero mark in the instrument used in taking a

Figure 2.41: Zero errors of a voltmeter measurement. These defects can

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Physics Form 1 Final.indd 53 16/10/2024 20:55