9th Physics Federal Board Notes: Unit 1 Physical Quantities and Measurement
📋 Table of Contents
- 1. Multiple Choice Questions
- 2. Short Response Questions
- 2.1 Role of Physics in Daily Life
- 2.2 Age Estimation in Minutes and Seconds
- 2.3 Base Quantities in Derived Quantities
- 2.4 Prefix Comparison: Micro vs Milli
- 2.5 Displacement vs Energy: Vector vs Scalar
- 2.6 Screw Gauge vs Vernier Calipers
- 2.7 Mechanical vs Digital Stopwatch
- 2.8 Measuring Volume with Cylinder
- 2.9 Precautions with Measuring Cylinder
- 2.10 Importance of Significant Digits
- 2.11 Reducing Random Errors
- 2.12 Precision vs Accuracy
- 3. Long Response Questions
- 3.1 Definition and Role of Physics
- 3.2 Branches of Physics
- 3.3 Physical Quantities: Base vs Derived
- 3.4 Units: Base vs Derived
- 3.5 Prefixes in Measurement
- 3.6 Scientific Notation
- 3.7 Vernier Calipers
- 3.8 Screw Gauge
- 3.9 Errors in Measurement
- 3.10 Scalars vs Vectors
- 3.11 Measuring Cylinder for Liquid Volume
- 3.12 Precision vs Accuracy
🔬 Introduction to Unit 1
Unit 1: Physical Quantities and Measurement forms the foundation of physics. This unit introduces students to the fundamental concepts of measurement, different types of physical quantities, units of measurement, and various measuring instruments. Understanding these concepts is crucial for all subsequent topics in physics as they provide the tools and methods for scientific inquiry and experimentation.
Multiple Choice Questions
Kilogram is a base unit in the International System of Units (SI), while pascal, newton, and watt are derived units. Pascal is derived from force and area (N/m²), newton from mass, length, and time (kg·m/s²), and watt from energy and time (J/s).
The mole is the SI base unit for measuring the amount of substance. It represents a specific number of particles (atoms, molecules, ions, etc.), which is approximately 6.022 × 10²³ particles (Avogadro's number).
The number 0.00650 has 3 significant figures. Leading zeros are not significant, but trailing zeros after a decimal point are significant. So the significant digits are 6, 5, and 0.
9000.8 has 5 significant figures. Let's check all options:
- A. 9000.8 → 5 significant figures
- B. 4 → 1 significant figure
- C. 5174.00 → 6 significant figures
- D. 0.001248 → 4 significant figures
Among the given prefixes:
- Mega (M) = 10⁶
- Pico (p) = 10⁻¹²
- Peta (P) = 10¹⁵
- Kilo (k) = 10³
A micrometer, also known as a micrometer screw gauge, is a precision instrument used for measuring small lengths, such as the diameter of wires or thickness of sheets, with high accuracy.
Vernier calipers have inside jaws specifically designed to measure internal dimensions like the diameter of pipes or containers. Screw gauges are better for measuring small external dimensions, while metre rules and measuring tapes lack the precision for such measurements.
Total reading = Main scale reading + (Circular scale reading × Least count)
= 0.03 mm
Mole is one of the seven base units in the International System of Units (SI). Pascal (pressure), coulomb (charge), and meter per second (speed) are all derived units.
Let's check the significant figures in each:
- A. 1.1 → 2 significant figures
- B. 6.0 → 2 significant figures
- C. 7.1 → 2 significant figures
- D. 6×10² → 1 significant figure (only the digit 6 is significant)
1 micrometer = 10⁻⁶ m
Ratio = (10⁻³ m) / (10⁻⁶ m) = 10³ = 1000
Short Response Questions
1. How physics plays an important role in our life?
🌍 Physics in Daily Life
Physics is fundamental to understanding and improving our daily lives. Its principles form the basis for most modern technologies and natural phenomena we encounter every day.
🏥 Medical Technology
Advanced medical devices like PET scans, MRI machines, and microscopic robots used in cancer treatment rely on principles of physics. These technologies enable precise diagnosis and targeted treatments.
🚗 Transportation
Physics principles are applied in designing vehicles, airplanes, and space shuttles. Concepts of mechanics, aerodynamics, and thermodynamics make modern transportation safe and efficient.
📱 Communication
Technologies like smartphones, computers, and the internet function based on electromagnetic waves and electronic circuits. Physics enables global connectivity and information exchange.
🏠 Household Appliances
Everyday gadgets like microwaves, refrigerators, and air conditioners work using principles of thermodynamics and electricity. Physics makes modern comfort and convenience possible.
2. Estimate your age in minutes and seconds.
⏰ Age Calculation
To calculate age in minutes and seconds, we use the following conversion factors:
- 1 year = 365 days
- 1 day = 24 hours
- 1 hour = 60 minutes
- 1 minute = 60 seconds
For a 15-year-old student:
= 15 × 365 × 1440
= 7,884,000 minutes
= 473,040,000 seconds
3. What base quantities are involved in these derived physical quantities; force, pressure, power and charge.
| Derived Quantity | Formula | Derived Unit | Base Quantities |
|---|---|---|---|
| Force (F) | F = m × a | Newton (N) = kg·m/s² | Mass, Length, Time |
| Pressure | P = F/A | Pascal (Pa) = N/m² = kg/(m·s²) | Mass, Length, Time |
| Power | P = W/t | Watt (W) = J/s = kg·m²/s³ | Mass, Length, Time |
| Charge | Q = I × t | Coulomb (C) = A·s | Electric Current, Time |
4. Show that prefix micro is thousand times smaller than prefix milli.
📏 Prefix Comparison
Let's compare the multipliers for micro and milli prefixes:
- Milli (m) = 10⁻³ = 0.001
- Micro (μ) = 10⁻⁶ = 0.000001
To find how many times micro is smaller than milli:
This shows that the prefix "micro" is 1000 times smaller than "milli".
Example: 1 millimeter = 1000 micrometers
5. Justify that displacement is a vector quantity while energy is a scalar quantity.
| Quantity | Type | Justification |
|---|---|---|
| Displacement | Vector | Displacement has both magnitude (distance) and direction (path from initial to final position). It follows vector addition rules and requires both numerical value and direction for complete description. |
| Energy | Scalar | Energy has only magnitude and no specific direction. Different forms of energy (kinetic, potential, thermal) can be added algebraically without considering direction. |
6. Screw gauge is more precise than vernier calipers. Justify.
| Instrument | Least Count | Precision | Application |
|---|---|---|---|
| Vernier Calipers | 0.01 cm or 0.1 mm | Good for measurements up to 0.1 mm | Measuring length, diameter, depth of objects |
| Screw Gauge | 0.001 cm or 0.01 mm | Higher precision for very small measurements | Measuring thickness of sheets, diameter of wires |
The screw gauge has a smaller least count (0.01 mm) compared to vernier calipers (0.1 mm), making it 10 times more precise. This higher precision makes screw gauge suitable for measuring very small dimensions where vernier calipers would not provide sufficient accuracy.
7. Differentiate between mechanical stopwatch and digital stopwatch.
| Aspect | Mechanical Stopwatch | Digital Stopwatch |
|---|---|---|
| Working Principle | Uses mechanical springs and gears | Uses electronic circuits and quartz crystal |
| Display | Analog dial with hands | Digital LCD or LED display |
| Accuracy | Less accurate, affected by temperature and wear | More accurate, consistent performance |
| Least Count | Typically 0.1 or 0.2 seconds | Typically 0.01 seconds |
| Operation | Manual winding and pressing buttons | Electronic buttons, often with memory function |
| Maintenance | Requires periodic servicing and oiling | Minimal maintenance, battery replacement |
8. How can we measure the volume of an irregular shaped solid with the help of measuring cylinder?
⚗️ Volume Measurement
The volume of an irregular solid can be measured using a measuring cylinder through the displacement method:
- Fill the measuring cylinder partially with water and note the initial volume (V₁)
- Carefully lower the irregular solid into the cylinder, ensuring it's completely submerged
- Note the new volume reading (V₂)
- Calculate the volume of the solid: V = V₂ - V₁
Example: If initial volume is 50 mL and final volume is 75 mL, then volume of solid = 75 - 50 = 25 mL = 25 cm³
9. What are the precautions for using measuring cylinder?
⚠️ Precautions with Measuring Cylinder
- Place the cylinder on a flat, stable surface before taking readings
- Keep the cylinder vertical while taking measurements
- Read the measurement at eye level to avoid parallax error
- Note the bottom of the meniscus (curved surface of liquid) for accurate reading
- Handle with care as glass cylinders are fragile
- Clean and dry the cylinder before use to avoid contamination
- Use appropriate size cylinder for the volume being measured for better accuracy
- Avoid sudden temperature changes that could cause breakage
10. Why significant digits are important in measurements?
🔢 Importance of Significant Figures
Significant digits are crucial in scientific measurements for several reasons:
- Indicate Precision: The number of significant digits reflects the precision of the measuring instrument
- Prevent False Accuracy: They prevent reporting measurements with more precision than the instrument can provide
- Standardize Reporting: Provide consistent rules for recording and communicating measurements
- Calculation Accuracy: Help maintain appropriate precision during mathematical operations
- Scientific Communication: Ensure clear understanding of measurement reliability among scientists
Example: Reporting a length as 2.5 cm (2 significant figures) indicates the measurement is precise to the nearest 0.1 cm, while 2.50 cm (3 significant figures) indicates precision to the nearest 0.01 cm.
11. How can we reduce random errors in measurement?
📊 Reducing Random Errors
Random errors are unpredictable fluctuations in measurements that can be minimized through these methods:
- Take Multiple Readings: Measure the same quantity several times and calculate the average
- Use Precise Instruments: Select instruments with smaller least counts
- Control Environmental Factors: Minimize temperature variations, vibrations, and air currents
- Improve Technique: Practice proper measurement techniques to reduce human error
- Use Statistical Methods: Apply standard deviation to understand the spread of measurements
- Calibrate Instruments: Regularly check and adjust instruments against standards
- Eliminate Parallax: Always read measurements at eye level perpendicular to the scale
12. Differentiate between precision and accuracy.
| Aspect | Precision | Accuracy |
|---|---|---|
| Definition | Closeness of measurements to each other | Closeness of measurements to the true value |
| Focus | Reproducibility and consistency | Correctness and validity |
| Error Type | Related to random errors | Related to systematic errors |
| Improvement | Take multiple measurements and average | Calibrate instruments and eliminate bias |
| Example | All measurements cluster together but away from true value | Measurements are close to true value but scattered |
| Visualization | Tight grouping of shots on a target | Shots centered on the bullseye |
Long Response Questions
1. Define physics. How physics play important role in our daily life?
🔭 Definition of Physics
Physics is the branch of science that deals with the study of matter, energy, and their interactions. It seeks to understand the fundamental principles governing the behavior of the universe through observation, experimentation, and mathematical analysis.
🏗️ Construction and Infrastructure
Physics principles ensure structural stability in buildings and bridges. Concepts of mechanics, material strength, and load distribution are crucial for safe construction practices and earthquake-resistant designs.
⚡ Energy Production
From hydroelectric dams to nuclear power plants, physics enables efficient energy generation and distribution. Understanding thermodynamics and electromagnetism is essential for meeting global energy demands.
🌤️ Weather Prediction
Meteorology relies on physics to understand atmospheric phenomena. Principles of fluid dynamics, thermodynamics, and radiation help predict weather patterns and climate changes.
🔊 Entertainment Technology
Audio systems, television, and digital media all function based on principles of sound waves, electromagnetism, and optics. Physics enhances our entertainment experiences through technological innovation.
2. Write a note on branches of physics.
📏 Mechanics
Study of motion, forces, and energy in physical systems. Includes kinematics, dynamics, and statics. Applications include vehicle design, structural engineering, and sports science.
⚡ Electromagnetism
Study of electric and magnetic fields and their interactions. Includes electrostatics, magnetostatics, and electromagnetic waves. Essential for electrical engineering and communications.
🔥 Thermodynamics
Study of heat, temperature, and energy transfer. Governs engines, refrigerators, and power plants. Key concepts include laws of thermodynamics and entropy.
💡 Optics
Study of light and its properties. Includes reflection, refraction, diffraction, and polarization. Applications in lenses, microscopes, telescopes, and fiber optics.
🔬 Atomic and Nuclear Physics
Study of atoms, atomic nuclei, and their interactions. Includes radioactivity, nuclear reactions, and particle physics. Applications in medicine, energy, and dating techniques.
🌀 Quantum Mechanics
Study of behavior of matter and energy at atomic and subatomic scales. Includes wave-particle duality and uncertainty principle. Foundation for modern electronics and materials science.
🌌 Relativity
Study of space, time, and gravity, especially at high speeds and strong gravitational fields. Includes special and general relativity. Essential for GPS and cosmology.
🔊 Acoustics
Study of sound waves and their propagation. Includes ultrasound, noise control, and architectural acoustics. Applications in music, medicine, and environmental science.
3. What are physical quantities? Differentiate between base and derived quantities.
📐 Physical Quantities
Physical quantities are properties of objects or phenomena that can be measured and expressed numerically with appropriate units. They form the language of physics for describing the physical world quantitatively.
| Aspect | Base Quantities | Derived Quantities |
|---|---|---|
| Definition | Fundamental quantities that are independent and cannot be defined in terms of other physical quantities | Quantities derived from base quantities through mathematical operations |
| Number in SI System | 7 base quantities | Unlimited derived quantities |
| Examples | Length, Mass, Time, Electric Current, Temperature, Amount of Substance, Luminous Intensity | Area, Volume, Speed, Acceleration, Force, Energy, Power, Pressure |
| Units | Base units (meter, kilogram, second, ampere, kelvin, mole, candela) | Derived units (m², m³, m/s, N, J, W, Pa) |
| Dependence | Independent of each other | Dependent on base quantities |
4. What are units? Differentiate between base and derived units.
📏 Units of Measurement
A unit is a standard quantity used for measurement of a physical quantity. It provides a reference for comparing measurements and ensures consistency in scientific communication.
| Aspect | Base Units | Derived Units |
|---|---|---|
| Definition | Units for base quantities that are defined independently | Units formed by combining base units according to the physical laws |
| Number in SI System | 7 base units | Many derived units with special names |
| Examples | Meter (m), Kilogram (kg), Second (s), Ampere (A), Kelvin (K), Mole (mol), Candela (cd) | Newton (N), Joule (J), Watt (W), Pascal (Pa), Hertz (Hz), Coulomb (C), Volt (V) |
| Symbols | Simple symbols (m, kg, s, A, K, mol, cd) | Compound symbols (N = kg·m/s², J = N·m, W = J/s) |
| Independence | Independent of other units | Dependent on base units |
5. What are prefixes? Explain with examples.
🔢 Prefixes in Measurement
Prefixes are symbols or words added before units to indicate multiples or fractions of those units. They help express very large or very small measurements conveniently without using scientific notation excessively.
| Prefix | Symbol | Multiplier | Example |
|---|---|---|---|
| Tera | T | 10¹² | 1 Tm = 1,000,000,000,000 m |
| Giga | G | 10⁹ | 1 GHz = 1,000,000,000 Hz |
| Mega | M | 10⁶ | 1 MW = 1,000,000 W |
| Kilo | k | 10³ | 1 km = 1000 m |
| Centi | c | 10⁻² | 1 cm = 0.01 m |
| Milli | m | 10⁻³ | 1 mm = 0.001 m |
| Micro | μ | 10⁻⁶ | 1 μm = 0.000001 m |
| Nano | n | 10⁻⁹ | 1 nm = 0.000000001 m |
| Pico | p | 10⁻¹² | 1 ps = 0.000000000001 s |
6. What is scientific notation? Write the following in scientific notation: 0.00556, 0.000000042, 4560000000000
📝 Scientific Notation
Scientific notation is a way of expressing numbers that are too large or too small to be conveniently written in decimal form. It follows the format:
Where N is a number between 1 and 10 (1 ≤ N < 10), and n is an integer exponent.
Conversion Examples:
0.000000042 = 4.2 × 10-8
4560000000000 = 4.56 × 1012
7. What is vernier calipers? Explain its working and use with the help of diagram.
📐 Vernier Calipers
Vernier calipers are precision instruments used to measure internal and external dimensions of objects with high accuracy. They consist of a main scale and a sliding vernier scale that allows measurements beyond the resolution of the main scale.
Main Parts of Vernier Calipers:
- Main Scale: Fixed scale with centimeter and millimeter divisions
- Vernier Scale: Sliding scale with 10 divisions equal to 9 mm
- Jaws: External jaws for measuring outer dimensions, internal jaws for inner dimensions
- Depth Rod: For measuring depth of holes or recesses
Working Principle:
The vernier scale has 10 divisions that cover 9 mm on the main scale, making each vernier division 0.9 mm. The difference between one main scale division (1 mm) and one vernier division (0.9 mm) is 0.1 mm, which is the least count.
= 1 mm - 0.9 mm = 0.1 mm = 0.01 cm
Measurement Procedure:
- Note the main scale reading just before the zero of vernier scale
- Find which vernier division coincides with a main scale division
- Multiply the vernier division number by least count (0.01 cm)
- Total reading = Main scale reading + (Vernier division × Least count)
8. What is screw gauge? Explain its working and use with the help of diagram.
🔧 Screw Gauge (Micrometer)
A screw gauge, also known as a micrometer screw gauge, is a precision instrument used for measuring small dimensions like the diameter of wires or thickness of sheets with very high accuracy.
Main Parts of Screw Gauge:
- U-shaped Frame: Provides stable support
- Anvil and Spindle: Surfaces between which the object is placed
- Main Scale (Sleeve): Linear scale along the barrel
- Circular Scale (Thimble): Rotating scale with divisions
- Ratchet: Ensures consistent pressure during measurement
Working Principle:
The screw gauge works on the principle of a screw. When the thimble is rotated, the spindle moves linearly. One complete rotation of the thimble moves the spindle by a fixed distance called the pitch.
Typically, pitch = 1 mm = 0.1 cm
Least Count = Pitch / Number of divisions on circular scale
Usually, Least Count = 1 mm / 100 = 0.01 mm = 0.001 cm
Measurement Procedure:
- Place the object between anvil and spindle
- Rotate the ratchet until the object is gently gripped
- Note the main scale reading (in mm)
- Note the circular scale division that coincides with the reference line
- Total reading = Main scale reading + (Circular scale reading × Least count)
9. What are errors? Explain different types of errors.
⚠️ Errors in Measurement
An error is the difference between the measured value and the true value of a quantity. No measurement can be perfectly accurate due to various limitations in instruments, observers, and environmental conditions.
Types of Errors:
| Error Type | Definition | Causes | Reduction Methods |
|---|---|---|---|
| Random Errors | Unpredictable fluctuations in measurements | Environmental changes, observer limitations, instrument vibrations | Take multiple readings and average, use precise instruments |
| Systematic Errors | Consistent deviation in one direction | Faulty calibration, incorrect zero setting, personal bias | Calibrate instruments, check zero error, use different methods |
| Zero Error | Instrument doesn't read zero when it should | Wear and tear, improper manufacturing, damage | Check and correct zero reading before measurements |
| Parallax Error | Error due to viewing measurement from wrong angle | Not reading scale at eye level perpendicularly | Always position eye perpendicular to scale |
| Instrumental Error | Error due to limitations of measuring instrument | Poor design, low resolution, wear of parts | Use better instruments, regular maintenance |
10. What are scalar and vector quantities? Differentiate between them with examples.
| Aspect | Scalar Quantities | Vector Quantities |
|---|---|---|
| Definition | Quantities with magnitude only | Quantities with both magnitude and direction |
| Representation | By a number and unit only | By magnitude, unit, and direction |
| Mathematical Operations | Follow ordinary algebra rules | Follow vector algebra rules |
| Addition | Added arithmetically | Added by triangle or parallelogram law |
| Examples | Mass, Time, Temperature, Energy, Speed, Distance, Volume | Displacement, Velocity, Acceleration, Force, Momentum, Weight |
| Change with Direction | Remain unchanged with direction change | Change with direction change |
| Component | No components | Can be resolved into components |
11. Explain how you can measure the volume of a liquid using measuring cylinder.
⚗️ Liquid Volume Measurement
A measuring cylinder is a common laboratory instrument used to measure the volume of liquids accurately. Here's the proper procedure:
Measurement Steps:
- Select an appropriate sized measuring cylinder for the volume to be measured
- Place the cylinder on a flat, stable surface
- Pour the liquid slowly into the cylinder
- Position your eyes at the same level as the liquid surface
- Note the reading at the bottom of the meniscus (the curved surface of the liquid)
- Record the volume with proper units and significant figures
Important Considerations:
- Meniscus Reading: For water and most liquids, read the bottom of the concave meniscus. For mercury, read the top of the convex meniscus.
- Temperature: Volume changes with temperature, so note if precision is required.
- Cleanliness: Ensure the cylinder is clean and dry before use.
- Accuracy: Use a cylinder with appropriate capacity for better accuracy.
12. Differentiate between precision and accuracy with examples.
| Aspect | Precision | Accuracy |
|---|---|---|
| Definition | Closeness of measurements to each other (reproducibility) | Closeness of measurements to the true value (correctness) |
| Focus | Consistency and repeatability of measurements | Validity and correctness of measurements |
| Error Type | Related to random errors | Related to systematic errors |
| Improvement Method | Take multiple readings and average them | Calibrate instruments and eliminate bias |
| Target Analogy | Shots clustered together but away from bullseye | Shots centered on bullseye but scattered |
| Example 1 | Three measurements: 2.51 g, 2.52 g, 2.51 g (precise but may not be accurate) | Three measurements: 2.48 g, 2.52 g, 2.50 g (accurate if true value is 2.50 g) |
| Example 2 | A clock that consistently runs 5 minutes fast is precise but inaccurate | A clock that shows correct time on average but varies is accurate but imprecise |
| Measurement Goal | Minimize spread of repeated measurements | Minimize difference from accepted value |
📚 Master 9th Physics
Understanding physical quantities and measurement is fundamental to all areas of physics. These concepts provide the foundation for scientific inquiry and experimentation. Continue your journey through the fascinating world of physics with our comprehensive notes for all units.
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Comprehensive study guide based on Federal Board curriculum with additional insights from educational resources
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