Chapter 1 Form 4 - Tutorial 2 (Physics)
Measurement and Vernier Caliper
1. We as a human frequently need to make measurements for physical quantities by using standard measuring instruments.
2. There are two types of errors
a) Systematic Errors
-Cumulative errors that can be corrected. Usually caused by the measuring instrument when it does not start exactly from zero. To correct it, the following equation can be used
Actual Reading = Measuring – Zero Error
Example: Zero Error
b) Random Errors
-Errors due to natural error or wrong techniques of measurement. To minimise the error, the position ot the eye must be in line with the reading, and for the instrument which have a scale and a pointer like an ammeter, a mirror is placed behind the pointer to minimise the error.
Example: Parallax Error
3. A pair of Vernier Calipers can be used to measure the thickness, diameter of a wire and depth of a liquid. Below is the picture of how the Vernier Calipers looks like.
4. The main scale is marked in divisions of 1mm, while the Vernier scale is marked in divisions of 0.1mm.
5. We need to check for zero error in order to obtain the accurate readings.
Micrometer Screw Gauge
1. The Micrometer Screw Gauge is used to measure very small thickness and diameters to the accuracy of 0.01mm.
2. Below are some of the error while taking the reading of the Micrometer Screw Gauge and ways to correct it.
Accuracy And Precision (Consistency)
1. Accuracy is the degree of a measuring instrument to record readings close to the actual values.
2. Precision/Consistency is the degree of a measuring instrument to record the consistent readings for each measurement by the same way.
3. Sensitivity is the degree of a measuring instrument to record the small change in its readings.
Accurancy
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Precision/Consistency
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Sensitivity
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How close the readings taken are to the actual value
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The consistency of the readings taken (less relative deviation)
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The ability of a measuring a small apparatus to detect small changes of the physical quantity
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To increase accurancy:
- Use more sensitive equipment
- Repeat reading taken
- Avoid Parallax Errors
- Avoid Zero Errors or end Edge Error
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To increase Precision:
- Use a magnifying glass when reading the scale
- Avoid Parallax Error
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To increase sensitivity (eg. Mercury thermometer)
- Use thin glass bulb wall
- Use a narrow capillary tube
- Use a smaller bulb size
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Experimental Errors
1. The systematic error is the error that appears in one direction only. The measurement obtained is deviated either consistently too high (always positive) or too low (always negative) from the actual value.
2. The sources of systematic error:
a. Zero Error of measuring instruments
b. Incorrectly Calibrated scale of measuring instruments
c. Repeated Error in reaction time
d. Wrong Assumption
3. Random Error has non-constant size of error and is unpredictable. The distribution of reading is sometimes positive and sometimes negative from the actual value. The sources of random error:
a. Parallax Error when reading a scale
b. Changes in the surroundings such as the temperature or pressure.
4. Random Error can be reduced by taking the mean value(average) of repeating measurements.
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