physics form 4

1. 1.4 Understanding Measurement
Ms. KONILIA M. S.

2. Error in Measurement
the difference between the actual value of a
quantity and the value obtained in measurement.
may occur due to incorrect skill of
handling the instruments or when
reading the data.
Error can be reduce if error are
known and how it happen

3. 2 Types of Error
•Systematic Error
•Random Error

4. Systematic errors
 tend to shift all measurements in a systematic way so their
mean value is displaced.
 can be compensated if the errors are known.
Examples of systematic errors
1. Zero error
o cause by an incorrect position of the zero point of measuring
instrument.
o consistently present in every reading of a measurement.
o can be positive or negative

6. 2. an incorrect calibration of the measuring
instrument.
3. consistently improper use of equipment.
Systematic error can be reduced by
1. Conducting the experiment with care.
2. Repeating the experiment by using different
instruments.

7. Random errors
 arise from unknown and unpredictable variations in condition.
 It vary from one measurement to the next.
 caused by factors that are beyond the control of the
observers.
 Factor of random error can cause by
1. personal errors such as human limitations of sight and
touch.
2. lack of sensitivity of the instrument: the instrument fail
to respond to the small change.
3. natural errors such as changes in temperature or wind,
while the experiment is in progress.
4. wrong technique of measurement (parallax error)

8. Parallax error
• error in reading an
instrument due to
the eye of the
observer and pointer
are not in a line
perpendicular to the
plane of the scale.

9. Random error can be reduced by
1. taking repeat readings.
2. find the average value of the reading.

10. Sensitivity of measuring instrument
• ability to detect small changes in the quantity
that is being measured.
• a sensitive instrument can quickly detect a
small change in measurement.
• Measuring instruments that have smaller
scale parts are more sensitive.
• Sensitive instruments need not necessarily be
accurate.

11. Try this!....
• Which instrument is more sensitive, a vernier
calliper or micrometer screw gauge?
• Why measurement of large quantities (kg or
km) does not required sensitive instrument?

12. Precision and Accuracy
Precision
• the ability of an instrument in measuring a
quantity in a consistent manner with only a small
relative deviation between readings.
• The precision of a reading can be indicated by its
relative deviation.
• Can be improve by:
Eliminating parallax error during measurement
Using instrument which is not defective.

13. Accuracy
• the approximation of the measurement to the actual
value.
• The measurement is more accurate if its number of
significant figures increases.
• The accuracy of a measurement can be increased by
1. repeat readings to calculate the mean value of the reading.
2. avoiding the end errors or zero errors.
3. taking into account the zero and parallax errors.
4. using more sensitive equipment such as a vernier caliper to
replace a ruler.