Physics Unit 1: Physical Quantities and Measurement
Multiple Choice Questions
1. Which one of the following unit is not a derived unit?
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Correct Answer: B. Kilogram is a base unit in SI, while pascal, newton, and watt are derived units.
2. Amount of a substance in terms of numbers is measured in:
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Correct Answer: D. The mole represents approximately 6.022 × 10²³ particles (Avogadro’s number).
3. The number of significant figures in 0.00650 s are:
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Correct Answer: B. 0.00650 has 3 significant figures. Leading zeros are not significant.
4. Which of the following numbers show 4 significant digits?
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Correct Answer: D. 0.001248 → 4 significant figures.
5. Which of the following prefix represents a largest value?
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Correct Answer: C. Peta (P) = 10¹⁵, which is the largest among given prefixes.
6. Micrometer can be used to measure:
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Correct Answer: C. Micrometer measures small lengths like wire diameter or sheet thickness.
7. The instrument that best measures the internal diameter of a pipe is:
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Correct Answer: B. Vernier calipers have inside jaws for internal measurements.
8. Least count of screw gauge is 0.01 mm. If main scale reading is zero and the third line of circular scale coincides, the measurement is:
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Correct Answer: C. Total reading = 0 + (3 × 0.01 mm) = 0.03 mm.
9. 9.483×10³ m is the standard form of:
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Correct Answer: D. 9.483 × 10³ = 9483 m.
10. Which of the following is a base unit?
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Correct Answer: D. Mole is a base unit; others are derived units.
11. The numbers having one significant digit is:
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Correct Answer: D. Only the digit 6 is significant.
12. Ratio of millimetre to micrometre is:
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Correct Answer: C. 1 mm / 1 μm = 10³ = 1000.
13. 0.2 mm in units of meters is:
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Correct Answer: C. 0.2 mm = 0.0002 m = 2×10⁻⁴ m.
2. 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 dayMedical 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.
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:
Age in minutes:
15 × 365 × 24 × 60 = 15 × 365 × 1440 = 7,884,000 minutes
Age in seconds:
7,884,000 × 60 = 473,040,000 seconds
1 year = 365 days
1 day = 24 hours
1 hour = 60 minutes
1 minute = 60 seconds
For a 15-year-old student:
Age in minutes:
15 × 365 × 24 × 60 = 15 × 365 × 1440 = 7,884,000 minutes
Age in seconds:
7,884,000 × 60 = 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) | P = F/A | Pascal (Pa) = N/m² = kg/(m·s²) | Mass, Length, Time |
| Power (P) | P = W/t | Watt (W) = J/s = kg·m²/s³ | Mass, Length, Time |
| Charge (Q) | Q = I × t | Coulomb (C) = A·s | Electric Current, Time |
4. Show that prefix micro is thousand times smaller than prefix milli.
Comparison of Multipliers:
Milli (m) = 10⁻³ = 0.001
Micro (μ) = 10⁻⁶ = 0.000001
Ratio: Milli / Micro = (10⁻³) / (10⁻⁶) = 10³ = 1000
Conclusion: The prefix “micro” is 1000 times smaller than “milli”.
Example: 1 millimeter = 1000 micrometers
Milli (m) = 10⁻³ = 0.001
Micro (μ) = 10⁻⁶ = 0.000001
Ratio: Milli / Micro = (10⁻³) / (10⁻⁶) = 10³ = 1000
Conclusion: 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.
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.
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 | PrecisionApplication | |
|---|---|---|---|
| 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 |
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 (Displacement Method):
The volume of an irregular solid can be measured using a measuring cylinder through the displacement method:
1. Fill the measuring cylinder partially with water and note the initial volume (V₁)
2. Carefully lower the irregular solid into the cylinder, ensuring it is completely submerged
3. Note the new volume reading (V₂)
4. Calculate the volume of the solid: V = V₂ – V₁
Example:
If initial volume is 50 mL and final volume is 75 mL,
Volume of solid = 75 − 50 = 25 mL = 25 cm³
💡 Practical Tip:
Use a thread to lower dense objects gently to avoid breaking the cylinder. For floating objects, use a sinker to submerge them completely.
The volume of an irregular solid can be measured using a measuring cylinder through the displacement method:
1. Fill the measuring cylinder partially with water and note the initial volume (V₁)
2. Carefully lower the irregular solid into the cylinder, ensuring it is completely submerged
3. Note the new volume reading (V₂)
4. Calculate the volume of the solid: V = V₂ – V₁
Example:
If initial volume is 50 mL and final volume is 75 mL,
Volume of solid = 75 − 50 = 25 mL = 25 cm³
💡 Practical Tip:
Use a thread to lower dense objects gently to avoid breaking the cylinder. For floating objects, use a sinker to submerge them completely.
9. What are the precautions for using measuring cylinder?
Precautions:
• 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
• 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:
• 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.
• 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 the following 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
Random errors are unpredictable fluctuations in measurements that can be minimized through the following 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 |