📌 Topics for Long Questions – Chapter 1 (Physical Quantities and Measurements)
In this chapter, the following topics are important for long questions in board exams:
1. Physical and Non-Physical Quantities
Define physical and non-physical quantities with examples. Explain the difference between them.
Key Points to Cover:
Physical Quantity: A quantity that can be measured (e.g., length, mass, time, temperature)
Non-Physical Quantity: A quantity that cannot be measured (e.g., love, beauty, happiness)
Physical quantities are measurable and have numerical values with units
Non-physical quantities are subjective and cannot be quantified
2. Base and Derived Physical Quantities
Define base and derived physical quantities. List the seven base quantities with their SI units.
Key Points to Cover:
Base Quantities: Fundamental quantities that cannot be derived from other quantities
Seven Base Quantities:
Length (meter)
Mass (kilogram)
Time (second)
Electric Current (ampere)
Temperature (kelvin)
Amount of Substance (mole)
Luminous Intensity (candela)
Derived Quantities: Quantities that are derived from base quantities (e.g., speed, force, pressure, volume)
3. Measurement of a Physical Quantity
Define measurement. Explain how a physical quantity is measured.
Key Points to Cover:
Measurement: The comparison of an unknown quantity with a standard quantity
Every measurement has two parts: Numerical Value and Unit
Example: Length = 5 m (5 is numerical value, m is unit)
Accuracy and precision are important in measurements
4. International System of Units (SI)
Explain the International System of Units (SI). Describe its advantages.
Key Points to Cover:
SI Units: Modern metric system adopted internationally
Advantages:
Internationally accepted
Coherent and consistent
Decimal-based for easy conversion
Based on fundamental constants
5. Derived Units
Define derived units with examples. Explain how derived units are formed from base units.
Key Points to Cover:
Derived Units: Units derived from base quantities
Examples:
Speed = m/s
Force = kg·m/s² (Newton)
Pressure = kg/(m·s²) (Pascal)
Volume = m³
Density = kg/m³
6. SI Prefixes
Explain SI prefixes used to express very large or very small quantities.
Key Points to Cover:
Prefixes: Added before units to represent multiples or fractions
Common Prefixes:
Giga (G) = 10⁹
Mega (M) = 10⁶
Kilo (k) = 10³
Hecto (h) = 10²
Deca (da) = 10¹
Deci (d) = 10⁻¹
Centi (c) = 10⁻²
Milli (m) = 10⁻³
Micro (μ) = 10⁻⁶
Nano (n) = 10⁻⁹
Pico (p) = 10⁻¹²
7. Scientific Notation
Explain scientific notation. Describe how to convert numbers into scientific notation.
Key Points to Cover:
Scientific Notation: Expressing numbers in the form a × 10ⁿ where 1 ≤ a < 10
Examples:
1500 = 1.5 × 10³
0.00025 = 2.5 × 10⁻⁴
Helps in writing very large or very small numbers conveniently
Useful in physics calculations
8. Length Measuring Instruments
Explain the instruments used to measure length.
Key Points to Cover:
Ruler/Meter Scale: For measuring length up to 1 mm accuracy
Vernier Callipers: For measuring length up to 0.01 mm accuracy
Micrometer Screw Gauge: For measuring length up to 0.001 mm accuracy
Choice of instrument depends on required precision
9. Vernier Callipers
Describe the construction and working of vernier callipers. Explain how to take a measurement.
Key Points to Cover:
Construction:
Main Scale (fixed)
Vernier Scale (movable)
Jaws (outer and inner)
Strip (depth measurement)
Least Count: Smallest value that can be measured
LC = 1 MSD – 1 VSD
For standard vernier: LC = 0.01 cm = 0.1 mm
How to Measure:
Place object between jaws
Read main scale reading
Read vernier scale reading
Total = MSR + (VSR × LC)
10. Measurement Using Vernier Callipers
Explain the step-by-step method of measuring length using vernier callipers.
Key Points to Cover:
Step 1: Check for zero error
Step 2: Place object between jaws and gently close
Step 3: Note main scale reading (MSR)
Step 4: Note vernier scale reading (VSR) – where lines coincide
Step 5: Apply formula: Length = MSR + (VSR × LC)
Step 6: If zero error exists, apply correction
11. Micrometer Screw Gauge
Describe the construction and working of micrometer screw gauge.
Key Points to Cover:
Construction:
U-shaped frame
Fixed stud (anvil)
Movable spindle (screw)
Main scale (on sleeve)
Circular scale (on thimble)
Ratchet
Least Count: LC = Pitch / Total divisions on circular scale
For standard micrometer: LC = 0.01 mm = 0.001 cm
12. Checking for Zero Error
Explain how to check for zero error in measuring instruments.
Key Points to Cover:
Zero Error: Error when instrument reads non-zero when measuring nothing
Positive Zero Error: When reading is positive with no object
Negative Zero Error: When reading is negative with no object
Correction: Subtract zero error from measured reading
Formula: Actual Reading = Observed Reading – Zero Error
13. Measurement Using Screw Gauge
Explain the step-by-step method of measuring length using screw gauge.
Key Points to Cover:
Step 1: Check for zero error
Step 2: Place object between anvil and spindle
Step 3: Turn ratchet until it clicks
Step 4: Note main scale reading (MSR)
Step 5: Note circular scale reading (CSR)
Step 6: Apply formula: Diameter = MSR + (CSR × LC)
Step 7: If zero error exists, apply correction
14. Mass Measuring Instruments
Explain the instruments used to measure mass.
Key Points to Cover:
Physical Balance: For measuring mass accurately
Beam Balance: Common laboratory balance
Electronic Balance: Digital balance for precise measurement
Triple Beam Balance: For measuring mass of objects
15. Physical Balance
Describe the construction and working of a physical balance.
Key Points to Cover:
Construction:
Beam
Two pans (left and right)
Pointer
Scale
Pillars
Leveling screws
Principle: Works on the principle of equal arms
How to Use:
Check zero position
Place object on left pan
Add standard masses on right pan until balanced
Read the total mass
16. Time Measuring Instruments
Explain the instruments used to measure time.
Key Points to Cover:
Stopwatch: For measuring time intervals accurately
Digital Stopwatch: Precise time measurement up to 0.01 seconds
Analog Clock: For general time reading
Digital Clock: For accurate time display
17. Stopwatch
Describe the construction and use of a stopwatch.
Key Points to Cover:
Analog Stopwatch: Has start, stop, and reset buttons
Digital Stopwatch: Displays time digitally with high precision
Least Count: 0.01 seconds for digital, 0.1 seconds for analog
Uses: Measuring time intervals in experiments
18. Volume Measuring Instruments
Explain the instruments used to measure volume.
Key Points to Cover:
Measuring Cylinder: For measuring liquid volume
Beaker: For approximate volume measurement
Pipette: For accurate transfer of liquids
Burette: For dispensing liquids accurately
Displacement Can: For measuring volume of irregular objects
19. Measuring Cylinder
Describe the construction and use of a measuring cylinder.
Key Points to Cover:
Construction: Graduated glass cylinder with markings
Use: To measure volume of liquids
Reading: Read at eye level, at the bottom of the meniscus
Least Count: Varies depending on cylinder size
Unit: Usually in milliliters (mL) or cubic centimeters (cm³)
20. Displacement Can Method
Explain the displacement can method for measuring volume of irregular objects.
Key Points to Cover:
Principle: Objects displace their own volume of water
Method:
Fill displacement can with water until it overflows
Place measuring cylinder under spout
Gently lower irregular object into water
Collect displaced water in measuring cylinder
Read volume of displaced water = Volume of object
This method works for irregular shapes
21. Errors in Measurements
Define measurement errors. Explain the different types of errors.
Key Points to Cover:
Error: Difference between measured and true value
Types of Errors:
Human Errors
Systematic Errors
Random Errors
Errors affect the accuracy and precision of measurements
22. Human Errors
Explain human errors in measurements.
Key Points to Cover:
Definition: Errors due to mistakes by the observer
Examples:
Parallax error (wrong angle of viewing)
Reading error (misreading scale)
Calculation error
Carelessness
How to Minimize: Careful observation, proper techniques
23. Systematic Errors
Explain systematic errors and their causes.
Key Points to Cover:
Definition: Errors that occur consistently in the same direction
Causes:
Faulty instruments (zero error)
Environmental conditions
Poor calibration
Characteristics: Always have same sign (positive or negative)
How to Minimize: Calibrate instruments, use correction factors
24. Random Errors
Explain random errors and their causes.
Key Points to Cover:
Definition: Errors that occur randomly with no fixed pattern
Causes:
Variations in environmental conditions
Observer’s personal limitations
Unpredictable fluctuations
Characteristics: Can be positive or negative
How to Minimize: Take multiple readings and calculate average
25. Uncertainty in a Measurement
Define uncertainty in measurements. Explain how to determine uncertainty.
Key Points to Cover:
Uncertainty: The doubt or lack of precision in a measurement
Absolute Uncertainty: Smallest division of the instrument
Relative Uncertainty: (Absolute Uncertainty / Measured Value) × 100
How to Express: Value ± Uncertainty (e.g., 5.0 ± 0.1 cm)
26. Significant Figures
Define significant figures. Explain the rules for counting significant figures.
Key Points to Cover:
Significant Figures: Digits that carry meaningful information
Rules:
Non-zero digits are always significant
Zeros between non-zero digits are significant
Leading zeros are NOT significant
Trailing zeros after decimal are significant
Trailing zeros without decimal are NOT significant
Examples:
2.5 has 2 SF
0.025 has 2 SF
2500 has 2 SF (unless specified)
has 4 SF
27. Precision and Accuracy
Differentiate between precision and accuracy with examples.
Key Points to Cover:
Precision: Closeness of repeated measurements to each other
Accuracy: Closeness of a measurement to the true value
Difference:
High precision but low accuracy: Consistent but wrong
Low precision but high accuracy: Inconsistent but correct
High precision and high accuracy: Consistent and correct
28. Rounding Off the Digits
Explain the rules for rounding off numbers to significant figures.
Key Points to Cover:
Rules:
If digit after last significant digit is < 5, keep it (round down)
If digit after last significant digit is ≥ 5, increase by 1 (round up)
Examples:
2.346 → 2.35 (3 SF)
2.341 → 2.34 (3 SF)
2.345 → 2.35 (3 SF)