📘 FORM FIVE PHYSICS
📏 TOPIC: MEASUREMENTS
1.0 MEANING OF MEASUREMENT
Measurement is the process of comparing a physical quantity with a standard unit.
Examples:
Length → metre (m)
Mass → kilogram (kg)
Time → second (s)
2.0 PHYSICAL QUANTITIES
(a) Fundamental (Base) Quantities
These are basic quantities that cannot be derived from others:
Quantity SI Unit
Length metre (m)
Mass kilogram (kg)
Time second (s)
Electric current ampere (A)
Temperature kelvin (K)
Amount of substance mole (mol)
Luminous intensity candela (cd)
(b) Derived Quantities
Formed from base quantities:
Quantity Formula
Area m²
Volume m³
Velocity m/s
Acceleration m/s²
Force kg m/s² (Newton)
3.0 UNITS AND SI SYSTEM
The SI system (International System of Units) is used worldwide to standardize measurements.
Advantages:
Universal
Easy conversion
Reduces confusion
4.0 ACCURACY AND PRECISION
(a) Accuracy
How close a measurement is to the true value.
(b) Precision
How close repeated measurements are to each other.
5.0 ERRORS IN MEASUREMENT
Types of errors:
1. Systematic Errors
Caused by faulty instruments
Same direction every time
2. Random Errors
Caused by human mistake or environment
Unpredictable
3. Gross Errors
Mistakes like reading wrong scale
6.0 SIGNIFICANT FIGURES
Rules:
All non-zero digits are significant
Zeros between digits are significant
Leading zeros are NOT significant
Example:
0.0045 → 2 significant figures
12.30 → 4 significant figures
7.0 DIMENSIONAL ANALYSIS
Used to:
Check correctness of equations
Convert units
Example:
Force = mass × acceleration
= kg × m/s²
= kg m s⁻²
📊 DIMENSIONAL FORMULAS
Quantity Dimensional Formula
Velocity [LT⁻¹]
Acceleration [LT⁻²]
Force [MLT⁻²]
Pressure [ML⁻¹T⁻²]
🧠 EXAM QUESTIONS
SECTION A: SHORT ANSWERS
1. Define measurement.
2. List five base SI quantities.
3. What is the SI unit of force?
4. Differentiate between accuracy and precision.
5. What is a derived quantity?
SECTION B: STRUCTURED QUESTIONS
6. (a) State three types of errors in measurement.
(b) Explain each type briefly.
7. (a) Define significant figures.
(b) Write 0.006780 in 3 significant figures.
8. (a) State two uses of dimensional analysis.
(b) Find the dimensional formula of energy.
SECTION C: PROBLEM SOLVING
9. A student measures length as 12.4 cm, 12.6 cm, 12.5 cm.
(a) Find average value.
(b) Comment on precision.
10. A force is given by F = ma.
If m = 5 kg and a = 2 m/s², calculate force and its SI unit.
🎯 ANSWERS (SHORT)
9(a) = (12.4 + 12.6 + 12.5)/3 = 12.5 cm
10 = F = 5 × 2 = 10 N
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