Chapter 1.4, The Use of Measuring Instruments, Accuracy, Consistency, Sensitivity and Errors
Chapter 1.4, The Use of Measuring Instruments, Accuracy, Consistency, Sensitivity and Errors
We need to ensure that we use the right measuring instruments to measure the quantities of length, mass, time, temperature and electric current accurately and consistently.
The Use of Right Measuring Instruments
Measuring Length
Length is the distance between two points. The S.L. unit for length is metre (m). Length can also be measured in millimetres (mm), centimetres (cm) or kilometres (km).
When using a ruler, the eyes of the observer must be parallel to the scale of the ruler to prevent parallax error (Figure 1.9). Parallax error occurs due to the wrong positioning of the eyes when taking measurements.
The Use of Measuring Instruments, Accuracy, Consistency, Sensitivity and Errors
For the purpose of measurement, different measuring instruments are needed to collect data in an experiment. We need to ensure that we use the right measuring instruments to measure the quantities of length, mass, time, temperature and electric current accurately and consistently.
Sensitivity - The ability of 1 measuring instruments to detect a small change in the measurement quantity.
Consistency- The ability of measuring instruments to give the same readings with repeated measurements.
Accuracy - - The ability of measuring instruments to obtain a value closest to the actual value.
The Use of Right Measuring Instruments
a) Measuring Length
Length is the distance between two points. The S.I. unit for length is metre (m). Length can also be measured in millimetres (mm), centimetres (cm) or kilometres (km).
When using a ruler, the eyes of the observer must be parallel to the scale of the ruler to prevent parallax error (Figure 1.9). Parallax error occurs due to the wrong positioning of the eyes when taking measurements.
b) Measuring Mass
The mass of an object is the quantity of matter in it. The S.I. unit for mass is kilogram (kg).
c) Measuring Time
The S.L. unit for time is second (s). Other units include minute (min), hour (hr), day, month, year and decade.
d) Measuring Temperature
Temperature is the degree of heat of an object. The S.I. unit for temperature is kelvin (K). However, degree Celsius (°C) is usually used as a measuring unit for temperature.
e) Measuring Electric Current
An ammeter is used to measure electric current in a circuit.
f) Measuring Volume of Water
A measuring cylinder can be used to measure the volume of water.
Using Measuring Instruments with higher Accuracy
A) Measuring Length
Vernier Callpiers
Vernier calipers is used to measure the thickness or outer diameter, inner diameter and depth of an object. The smallest division of the reading of a vernier calipers is 0.01 cm or 0.1 mm. Therefore, vernier calipers is much more accurate compared to a ruler which can only measure the smallest reading up to 0.1 cm or 1 mm.
Text book
To determine the positive zero error, the error has to be read from the "0" mark on the vernier scale. To determine the negative zero error, the error has to be read from the "10" mark on the vernier scale.
Micrometre screw gauge A micrometer screw gauge is used to measure the thickness and diameter of small objects like paper and hair. The smallest division of the micrometer screw gauge's reading is 0.001 cm or 0.01 mm. Therefore, the micrometer screw gauge is more accurate than the vernier calipers.
The vernier scale has 50 divisions. Each division on the vernier scale is 0.01 mm.
The eyes of the reader should be perpendicular to the reading to prevent parallax error.
Making an estimation before making and actual measurement
b) estimating area
click to edit
click to edit
How to minimize systematic errors and random errors
Systematic errors
Random errors
a) estimating length
Activity 1.9 Aim: To make a link between making estimation and taking the actual measurement
Materials and Apparatus: Pencil and ruler Instruction 1. Measure the length of a pencil (p cm). 2. Measure and record the length of a table using the pencil. Length of the table = number of pencil x p cm 3. Measure and record the length of the table using a ruler. Question: what is the difference between the length of the table measured using a ruler (actual measurement)?
Area is the size of a surface. The S.I. unit for area is m². For objects with regular shapes, area can be measured by using formulae. For example, the area of a square is length x width. What is the formula of the area of other objects as shown in Figure 1.19?
For objects with irregular shapes, area can be estimated by using the graph paper method.
Example
Using Measuring Instruments with higher accuracy
b) measuring mass
c) measuring time
d) measuring temperature
e) measuring electric current
digital electronic balance
digital stopwatch
thermometer
ammeter
Technology and innovation in measuring instruments
Consistent errors obtained from a measuring instrument for every measurement
The uncertainties in measurement caused by the observer when taking measurements
Example: Zero error, inaccurate measuring instrument
Ways to overcome:
Conduct experiments with caution
Repeat the experiment using different measuring instruments
Examples:
Parallax error
Carelessness of observer when taking the reading
Wrong technique
Ways to overcome
Take a few readings of measurement and take the average reading
To reduce the impact of parallax errors, the observer's eyes should be perpendicular to the scale reading
Measuring blood pressure is made easier by using the digital blood pressure monitor (Photograph 1.24). Patients who have blood pressure problems can obtain precise and reliable blood pressure reading within a few seconds. Can you give examples of other types of innovation in measuring instruments?