π Chapter 1: Physical Quantities and Measurements β Short Questions
Prepared by Muhammad Tayyab, Subject Specialist Physics, Govt Christian High School Daska. Based on PECTAA 2026 syllabus (National Curriculum 2023).
π What's Inside: This section covers short questions from Chapter 1 Physical Quantities and Measurements including science, physical and non-physical quantities, base and derived quantities, SI units, prefixes, scientific notation, measuring instruments (metre rule, measuring tape, Vernier Callipers, screw gauge, stopwatch, measuring cylinder), errors (human, systematic, random), significant figures, precision and accuracy. Each question is presented with a precise answer as per the official PECTAA 2026 Physics curriculum. Perfect for Punjab Boards (Lahore, Gujranwala, Multan, etc.) and all BISE boards across Pakistan.
π Related Resources β Chapter 1: Physical Quantities and Measurements
π Exercise Short Qs
π Short Qs
π Comprehensive Qs
π’ Numerical Problems
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MCQs
βοΈ Constructed Response
Physical Quantities and Measurements covers fundamental concepts of measurement, SI units, and measuring instruments.
π Quick Jump to Questions
π Short Questions & Answers (PECTAA 2026)
1 What is science?
Answer: This field of observation and experimentation to understand about the world around us is known as science.
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Science: Observation and experimentation to understand the world.
2 What are physical and non-physical quantities?
Answer:
Physical Quantities: Physical quantities are quantities that can be measured directly or indirectly using tools and instruments, such as the length of an object using a ruler, the time duration of an event using a clock.
Non-physical Quantities: Quantities that cannot be measured using tools and instruments. They mostly help to understand and analyze human behavior, emotions, and social interactions. For example, love, affection, fear, wisdom, and beauty etc.
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Physical: Measurable. Non-physical: Cannot be measured (e.g., love, fear).
3 Is a non-physical quantity has dimensions?
Answer: No, non-physical quantities do not have dimensions because they cannot be measured.
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Non-physical quantities have no dimensions.
4 What is difference between base quantities and derived physical quantities?
Answer:
| Base Quantities | Derived Quantities |
|---|---|
| Quantities selected arbitrarily by scientists to play a key role in describing physical phenomena. | Quantities that can be described in terms of one or more base quantities. |
| Base quantities are length, mass, time, temperature, electric current, etc. | For example, speed is a derived quantity depending on distance and time. |
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Base: Arbitrarily selected (length, mass, time). Derived: From base quantities (speed, area, volume).
5 What is measurement? Name its two parts.
Answer: Measurement is a process of comparison of an unknown quantity with a widely accepted standard quantity. Its two parts are: (i) A number (magnitude). (ii) A unit (standard of measurement).
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Measurement: Comparison with a standard. Two parts: Number and Unit.
6 What is a Unit?
Answer: The standard amount of a physical quantity, which is used to compare larger or smaller amounts, is called the unit.
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Unit: Standard amount for comparison.
7 What is the International System of Units (SI)? Also write its advantage.
Answer: The International System of Units (SI) is a system of measurement consisting of seven base units, recommended by the international committee on weights and measures in 1961.
Advantage: The SI system is used all over the world, enabling scientists to share and compare their observations and results easily.
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SI: Seven base units. Advantage: Global standardization.
8 What is difference between Base Units and Derived Units?
Answer:
Base Units: Base units cannot be derived from one another and cannot be resolved into anything more basic.
| No. | Physical quantity | Unit | Symbol |
|---|---|---|---|
| 1 | Length | metre | m |
| 2 | Mass | kilogram | kg |
| 3 | Time | second | s |
| 4 | Temperature | kelvin | K |
| 5 | Electric current | ampere | A |
| 6 | Intensity of light | candela | cd |
| 7 | Amount of substance | mole | mol |
Derived Units: Derived units are the units of quantities that can be expressed in terms of base units.
| No. | Physical quantity | Unit | Symbol |
|---|---|---|---|
| 1 | Area | square metre | mΒ² |
| 2 | Volume | cubic metre | mΒ³ |
| 3 | Speed | metre per second | ms-1 |
| 4 | Force | newton | N |
| 5 | Pressure | pascal | Pa |
| 6 | Electric charge | coulomb | C |
| 7 | Plane angle | radian | rad |
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Base units: Independent (m, kg, s). Derived units: From base units (mΒ², mΒ³, ms-1).
9 Define SI prefixes and explain their advantage.
Answer: Prefixes are the words or symbols added before SI unit such as milli, centi, kilo, mega, giga etc. Prefixes helps simplify large or small quantities for convenience.
| Type | Prefix | Symbol | Powers of Ten |
|---|---|---|---|
| Sub-multiples | atto | a | 10-18 |
| femto | f | 10-15 | |
| pico | p | 10-12 | |
| nano | n | 10-9 | |
| micro | ΞΌ | 10-6 | |
| milli | m | 10-3 | |
| centi | c | 10-2 | |
| deci | d | 10-1 | |
| Multiples | kilo | k | 103 |
| mega | M | 106 | |
| giga | G | 109 | |
| tera | T | 1012 | |
| peta | P | 1015 | |
| exa | E | 1018 |
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Prefixes simplify large/small quantities (e.g., 50,000,000 m = 5 Γ 10β· m).
10 What is scientific notation?
Answer: Scientific notation is a method of representing very large or very small numbers in a compact form. It expresses numbers as a product of a number between 1 and 10, multiplied by a power of 10.
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Scientific notation: \(N \times 10^n\) where \(1 \le N < 10\).
11 What is a metre rule? Also define least count.
Answer: A metre rule is commonly used in laboratories to measure length. The smallest division on a metre rule is \(1 \text{ mm}\), which is known as the least count of the metre rule.
Least count: The least count is the smallest measurement that can be accurately taken with an instrument.
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Metre rule: Measures length. Least count = 1 mm.
12 What is parallax error and how can it be avoided?
Answer: Parallax error occurs due to the incorrect position of the eye when taking measurements. This results in inaccurate readings. It can be avoided by keeping the line of sight directly above and perpendicular to the scale mark being read.
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Parallax error: Eye position error. Avoid by keeping eye perpendicular to scale.
13 What is a measuring tape, and what is its least count?
Answer: A measuring tape is used to measure lengths ranging from \(1 \text{ mm}\) to several metres. Its least count is \(1 \text{ mm}\).
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Measuring tape: Measures up to several metres. Least count = 1 mm.
14 What is a Vernier Callipers? For what purpose, a Vernier Callipers is used?
Answer: The Vernier Calliper is an instrument used to measure small lengths with high precision, down to \(\frac{1}{10}\) th of a millimetre. It can measure the thickness, diameter, width, or depth of an object.
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Vernier Callipers: Measures small lengths precisely (0.1 mm).
15 How is the least count of a Vernier Calliper determined?
Answer: The least count of a Vernier Calliper is the difference between one main scale division (\(1 \text{ mm}\)) and one Vernier scale division (\(0.9 \text{ mm}\)). Hence, least count = \(1 \text{ M.S div} - 1 \text{ V.S div} = 1 \text{ mm} - 0.9 \text{ mm} = 0.1 \text{ mm}\).
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The least count is usually found by dividing the length of one small division on the main scale by the total number of divisions on the Vernier scale. For example,
\[L.C = \frac{\text{Smallest reading on main scale}}{\text{Total no. of divisions on vernier scale}} = \frac{1 \text{ mm}}{10} = 0.1 \text{ mm} = 0.01 \text{ cm}\]
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Least count = 1 M.S div - 1 V.S div = 0.1 mm = 0.01 cm.
16 What is zero error in Vernier Callipers, and when does it occur?
Answer: Zero error occurs if, on joining the jaws of Vernier Callipers, the zeros of the main scale and Vernier scale do not exactly coincide with each other. This error in the instrument is called zero error.
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Zero error: Non-coinciding zeros when jaws are closed.
17 Differentiate between positive and negative zero error in Vernier Callipers.
Answer:
Positive Zero Error: Occurs when the zero of the Vernier scale lies to the right side of the main scale zero; it is corrected by subtracting the value from observed readings.
Negative Zero Error: Occurs when the zero of the Vernier scale lies to the left side of the main scale zero; it is corrected by adding the value to observed readings.
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Positive: Vernier zero right of main zero (subtract). Negative: Vernier zero left of main zero (add).
18 What is a Screw Gauge, and how is it used to measure small lengths?
Answer: Screw gauge is an instrument which can measure length correct up to \(0.01 \text{ mm}\).
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Screw gauge: Measures lengths up to 0.01 mm precision.
19 What is the pitch of a screw gauge?
Answer: The pitch of the screw gauge is the distance the spindle moves along the main scale when the thimble completes one full rotation. For example, if the spindle moves \(0.5 \text{ mm}\) in one complete turn, the pitch is \(0.5 \text{ mm}\).
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Pitch: Distance moved in one full rotation.
20 Define least count of screw gauge.
Answer: The least count of a screw gauge is calculated using the formula:
\[ \text{Least Count} = \frac{\text{Pitch of the Screw Gauge}}{\text{Number of Divisions on the Circular Scale}} \]
\[ \text{Least Count} = \frac{0.5 \text{ mm}}{50} = 0.01 \text{ mm or } 0.001 \text{ cm} \]
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Least count = Pitch / Number of circular divisions = 0.01 mm.
21 What is zero error in a screw gauge?
Answer: Zero error in a screw gauge occurs when the zero of the circular scale does not coincide with the horizontal line of the main scale when the anvil and spindle are fully closed.
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Screw gauge zero error: Circular scale zero not aligned with main scale when closed.
22 Differentiate between mass and weight.
Answer:
| Mass | Weight |
|---|---|
| Mass is the measure of the quantity of matter in a body. | Weight is the force by which a body is attracted toward the Earth. |
| Measured in kilograms (kg) or grams (g). | Measured in Newtons (N). |
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Mass: Matter quantity (kg). Weight: Gravitational force (N).
23 What is a physical balance?
Answer: In laboratories, we use physical balance which is based on the principle of lever.
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Physical balance: Based on lever principle.
24 What is a stopwatch?
Answer: The duration of an event is measured by a stopwatch, which contains two needles: one for seconds and one for minutes.
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Stopwatch: Measures duration with seconds and minutes needles.
25 Compare mechanical and digital stopwatches.
Answer: A mechanical stopwatch uses two hands and a top knob to measure time intervals to a least count of \(\frac{1}{10} = 0.1 \text{ s}\). A digital/electronic stopwatch measures time electronically on a screen down to a least count of \(\frac{1}{100} \text{ s} = 0.01 \text{ s}\).
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Mechanical: 0.1 s least count. Digital: 0.01 s least count.
26 What is a measuring cylinder and what is it used for?
Answer: A measuring cylinder is a cylinder made of glass or transparent plastic, with a scale marked in cubic centimeters (\(\text{cm}^3\) or cc) or milliliters (\(\text{mL}\)). It is used to find the volume of liquids and non-dissolvable solids.
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Measuring cylinder: Measures volume of liquids and solids.
27 What is meniscus?
Answer: The meniscus is the curved surface of the liquid. For water, the surface curves downward, and the reading is taken at the bottom edge of the meniscus. For mercury, which curves upward, the reading is taken at the top edge of the meniscus.
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Meniscus: Curved liquid surface. Water: read bottom. Mercury: read top.
28 Describe human errors in measurements and how to reduce them.
Answer: Human errors occur due to personal performance factors, such as faulty procedures when reading a scale, reaction time delays, or inaccurate estimation. They are reduced by proper technique training, focusing, or switching to digital automated instruments.
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Human errors: Due to personal factors. Reduce by training and automation.
29 What are systematic errors and how can they be minimized?
Answer: Systematic errors are consistent errors that affect all readings equally due to instrument zero errors, poor calibration, or incorrect scale markings. They can be reduced by comparing the instrument against a standard calibrated model and applying a correction factor.
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Systematic errors: Consistent errors. Reduce by calibration and correction.
30 What are random errors and how can their effect be minimized?
Answer: Random errors occur when repeated measurements yield different values under identical conditions due to unknown, unpredictable fluctuations in environment (e.g., temperature, pressure, or voltage). Their effect is reduced by taking multiple readings and calculating their average (mean) value.
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Random errors: Unpredictable fluctuations. Reduce by averaging multiple readings.
31 What is uncertainty in measurement?
Answer: Uncertainty is the range of possible error in a measurement, showing how much the measured value may differ from the true value due to limitations of instruments or methods.
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Uncertainty: Range of possible error in measurement.
32 Name some repetitive processes occurring in nature which could serve as reasonable time standard.
Answer: The period of oscillation of a pendulum, rotation of Earth, etc.
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Natural time standards: Pendulum oscillation, Earth's rotation.
33 Define significant figures.
Answer: Significant figures (or digits) are the digits of a measurement that are reliably known. They include all the accurately known digits and the first doubtful digit, which is determined by estimation and has a probability of error.
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Significant figures: Reliably known digits including one estimated digit.
34 What are the rules for determining the number of significant figures in a measurement?
Answer: The following rules help determine the significant figures in a measurement:
(a) All digits from 1 to 9 are significant. Example: 345 m has 3 significant figures.
(b) Zeros may or may not be significant:
(i) Zero between digits is significant. Example: In \(5.06 \text{ m}\), the zero between 5 and 6 is significant, so the number has 3 significant figures.
(ii) Zeros on the left side of a measured value are not significant. Example: In \(0.0034 \text{ m}\), the zeros before 3 and 4 are not significant, so the number has 2 significant figures.
(iii) Zeros to the right of a decimal are significant. Example: In \(2.40 \text{ mm}\), the zero after 4 is significant, so the number has 3 significant figures.
(iv) In scientific notation, all digits before the exponent are significant. Example: In \(3.50 \times 10^{4} \text{ m}\), all digits (3, 5, and 0) are significant, so the number has 3 significant figures.
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Rules: Non-zero digits significant. Zeros between digits significant. Leading zeros not significant. Trailing zeros after decimal significant.
35 What is the difference between precision and accuracy in physical measurements?
Answer:
Precision: Precision refers to how close together a group of measurements are.
Accuracy: Accuracy refers to how close the measured value is to the true value.
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Precision: Consistency of measurements. Accuracy: Closeness to true value.
π Key Formulas β Physical Quantities and Measurements
Least Count of Vernier Callipers: \( L.C = \frac{\text{Smallest reading on main scale}}{\text{Total no. of divisions on vernier scale}} \)
Least Count of Screw Gauge: \( L.C = \frac{\text{Pitch}}{\text{Number of divisions on circular scale}} \)
Scientific Notation: \( N \times 10^n \) where \( 1 \le N < 10 \)
π‘ Exam Tip:
For short questions, always write precise and to-the-point answers. Use key terms like "science", "physical quantities", "base quantities", "derived quantities", "SI units", "Vernier Callipers", "least count", "zero error", "systematic errors", "random errors", "significant figures", and "precision/accuracy" as they are commonly tested in exams. These questions follow the PECTAA 2026 pattern and are prepared by Subject Specialist Muhammad Tayyab.
Chapter 1β¨ Physical Quantities and Measurements
Chapter 2Kinematics
Chapter 3Dynamics
Chapter 4Turning Effect of Forces
Chapter 5Work and Energy
Chapter 6Mechanical Properties of Matter
Chapter 7Thermal Properties of Matter
Chapter 8Magnetism
Chapter 9Nature of Science
π Complete syllabus coverage for Class 9 Physics (PECTAA 2026) β Chapters 1 to 9
Created by Hira Science Academy | Aligned with PECTAA 2026 Syllabus