Chapter -1.1 "Physical quantities and measurement techniques" - Short Question

1.1 Physical Quantities and Measurement Techniques

Q1. State the SI unit of length.

Answer: metre (m)

Q2. Name the instrument used to measure length in the laboratory.

Answer: Ruler or metre rule

Q3. What is the smallest division on a typical school ruler?

Answer: 1 mm

Q4. Define parallax error.

Answer: Error caused when the scale is read from an angle instead of at eye level.

Q5. How can parallax error be avoided when using a ruler?

Answer: Read the scale at eye level directly above the marking.

Q6. Why should repeated measurements be taken?

Answer: To reduce random error and improve reliability.

Q7. A student measures from 2.0 cm to 7.5 cm. Calculate the length.

Answer:

Length = 7.5 − 2.0 = 5.5 cm

Q8. Why is it better to measure 10 sheets of paper instead of one sheet?

Answer: To reduce percentage uncertainty.

Q9. Where is the length of a pendulum measured from?

Answer: From pivot to centre of the bob.

Q10. State one precaution when measuring a curved object.

Answer: Use a string to follow the curve and then measure the string with a ruler.

Q11. State the unit used for volume in a measuring cylinder.

Answer: millilitre (mL) or cubic centimetre (cm³)

Q12. State the relationship between cm³ and mL.

Answer: 1 cm³ = 1 mL

Q13. What is the curved surface of a liquid in a measuring cylinder called?

Answer: Meniscus

Q14. Where should the volume be read for water?

Answer: At the bottom of the meniscus.

Q15. Why must the measuring cylinder be placed on a flat surface?

Answer: To ensure accurate reading.

Q16. A stone is placed in water. Water rises from 30 mL to 44 mL. Calculate the volume of the stone.

Answer:

Volume = 44 − 30 = 14 mL

Q17. Name the method used to measure the volume of an irregular solid.

Answer: Water displacement method.

Q18. State one source of error when using a measuring cylinder.

Answer: Parallax error.

Q19. What is the uncertainty if the smallest division is 2 mL?

Answer: ±1 mL

Q20. Define percentage error.

Answer: (Uncertainty ÷ Measured value) × 100

Q21. Define accuracy.

Answer: Closeness of a measured value to the true value.

Q22. Define precision.

Answer: How close repeated measurements are to each other.

Q23. Why should the smallest possible measuring cylinder be used?

Answer: To increase accuracy and reduce percentage error.

Q24. State one advantage of taking the average of readings.

Answer: Reduces effect of random errors.

Q25. State one precaution when measuring liquid volume.

Answer: Read the scale at eye level.

Q26. Convert 35 cm into metres.

Answer:

35 ÷ 100 = 0.35 m

Q27. Convert 4.5 m into centimetres.

Answer:

4.5 × 100 = 450 cm

Q28. A ruler has 1 mm divisions. State its precision.

Answer: ±0.5 mm

Q29. Why is the zero mark sometimes avoided when measuring?

Answer: It may be worn or damaged, causing error.

Q30. State one reason why air bubbles affect displacement readings.

Answer: They increase the apparent volume measured.

Q31. State the SI unit of time. 

Answer: Second (s).

Explanation: The second is the base SI unit used for measuring time in Physics.

Q32. Name two instruments used to measure time intervals. 

Answer: Stopwatch and digital timer.

Explanation: Both instruments are designed to measure time intervals accurately in experiments.

Q33. What is meant by the period of a pendulum?

Answer: The period is the time taken for one complete oscillation.

Explanation: One oscillation means one full back and forth movement.

Q34. A pendulum takes 30 s to complete 15 oscillations. Calculate the period. 

Answer:

Period = 30 ÷ 15 = 2 s.

Explanation: Period is found by dividing total time by number of oscillations.

Q35. Why is it better to time 20 oscillations instead of one? 

Answer: It reduces percentage uncertainty.

Explanation: Measuring a longer total time makes the effect of reaction time smaller compared to the total time measured.

Q36. Define frequency. 

Answer: Frequency is the number of oscillations per second.

Explanation: It tells how many complete cycles occur in one second and is measured in hertz (Hz).

Q37. Write the formula relating frequency and period. 

Answer:

Frequency = 1 ÷ Period

Explanation: Frequency and period are inversely related.

Q38. A period is 0.5 s. Calculate the frequency. 

Answer:

Frequency = 1 ÷ 0.5 = 2 Hz.

Explanation: One divided by 0.5 equals 2 oscillations per second.

Q39. State one disadvantage of using a stopwatch. 

Answer: Reaction time error.

Explanation: Human delay when pressing start or stop introduces error.

Q40. What type of error is caused by reaction time? 

Answer: Random error.

Explanation: Reaction time varies each time, so it is not consistent.

Q41. Why should a pendulum be released at a small angle? 

Answer: To keep the motion regular and period consistent.

Explanation: Large angles may slightly change the time of oscillation.

Q42. A student records 10 s for 5 oscillations. Calculate the frequency. 

Answer:

Period = 10 ÷ 5 = 2 s

Frequency = 1 ÷ 2 = 0.5 Hz

Explanation: First find period, then calculate frequency.

Q43. What is the advantage of using a digital timer with light gates? 

Answer: It removes reaction time error and increases accuracy.

Explanation: The timer starts and stops automatically using sensors.

Q44. Convert 2 minutes into seconds. 

Answer:

2 × 60 = 120 s.

Explanation: 1 minute equals 60 seconds.

Q45. Define uncertainty in time measurement. 

Answer: Uncertainty is the possible range within which the true value lies.

Explanation: It is usually half the smallest scale division of the instrument.

Q46. A stopwatch reads to 0.1 s. What is its uncertainty? 

Answer: ±0.1 s.

Explanation: The uncertainty is approximately equal to the smallest division.

Q47. Why should measurements be repeated? 

Answer: To reduce random error and improve reliability.

Explanation: Averaging repeated readings gives a more accurate result.

Q48. A student times 40 oscillations in 20 s. Calculate the period. 

Answer:

Period = 20 ÷ 40 = 0.5 s.

Explanation: Divide total time by number of oscillations.

Q49. If total time for 50 oscillations is 25 s, what is the frequency? 

Answer:

Frequency = Number of oscillations ÷ Time

Frequency = 50 ÷ 25 = 2 Hz

Explanation: Frequency is oscillations per second.

Q50. State one precaution when counting oscillations. 

Answer: Use a fixed reference point.

Explanation: Counting each time the pendulum passes the same point avoids mistakes.

Q51. Define random error. 
Answer: Random error is an unpredictable variation in measurement that causes readings to fluctuate above or below the true value.
Explanation: It occurs due to reaction time, small environmental changes, or instrument limitations.

Q52. Why is a single reading often unreliable? 
Answer: A single reading may be affected by random error and may not represent the true value.
Explanation: Without repetition, there is no way to check consistency.

Q53. State the formula for calculating an average value. 
Answer:
Average = Sum of readings ÷ Number of readings
Explanation: This formula combines all readings and divides by the total number taken.

Q54. A student records 8.0 s, 8.2 s, and 7.8 s. Calculate the average. 
Answer:
Sum = 8.0 + 8.2 + 7.8 = 24.0
Average = 24.0 ÷ 3 = 8.0 s
Explanation: The higher and lower values balance out.

Q55. What is an anomalous result? 
Answer: A result that is very different from other readings.
Explanation: It does not follow the general pattern of results.

Q56. Give one reason why an anomalous reading may occur. 
Answer: Misreading the instrument.
Explanation: Human error can produce an unusual value.

Q57. Why should anomalous results be checked? 
Answer: To confirm whether it was a mistake before excluding it.
Explanation: Excluding results without justification reduces reliability.

Q58. Define reliability. 
Answer: Reliability is the consistency of repeated measurements.
Explanation: Results are reliable if they are close to each other.

Q59. Define accuracy. 
Answer: Accuracy is how close a measurement is to the true value.
Explanation: Accurate results are near the correct value.

Q60. How does averaging improve reliability? 
Answer: It reduces the effect of random errors by balancing higher and lower readings.
Explanation: The final value becomes more consistent.

Q61. A student measures 2.0 mm, 2.1 mm, and 1.9 mm. Calculate the average thickness. 
Answer:
Sum = 2.0 + 2.1 + 1.9 = 6.0
Average = 6.0 ÷ 3 = 2.0 mm
Explanation: The average gives a more reliable value.

Q62. Why does measuring many sheets of paper reduce percentage uncertainty? 
Answer: The measured value increases while uncertainty stays the same.
Explanation: Percentage uncertainty decreases when measured value increases.

Q63. Write the formula for percentage uncertainty. 
Answer:
Percentage uncertainty = (Uncertainty ÷ Measured value) × 100

Q64. If uncertainty is ±0.5 cm and measured value is 5 cm, calculate percentage uncertainty. 
Answer:
(0.5 ÷ 5) × 100 = 10%
Explanation: The uncertainty is large compared to the measurement.

Q65. Why is timing 20 oscillations better than timing one? 
Answer: It reduces percentage uncertainty.
Explanation: Larger total time reduces effect of reaction time error.

Q66. What happens to percentage uncertainty if measured value increases? 
Answer: It decreases.
Explanation: Because uncertainty becomes smaller relative to the value.

Q67. A student records 10 s, 10 s, and 15 s. What should be done? 
Answer: Check the 15 s reading and repeat the measurement.
Explanation: 15 s may be anomalous.

Q68. Why should results be recorded with units? 
Answer: To clearly indicate the quantity being measured.
Explanation: Units are essential for correct scientific reporting.

Q69. What does a large spread of results indicate? 
Answer: Poor reliability.
Explanation: The experiment may contain significant random errors.

Q70. Why is averaging especially important for short time intervals? 
Answer: Because reaction time error becomes large compared to small time values.
Explanation: Averaging reduces the effect of this error.

Q71. Define a scalar quantity. 

Answer: A scalar quantity has magnitude only and no direction.

Explanation: It is fully described by its size and unit.

Q72. Define a vector quantity. 

Answer: A vector quantity has both magnitude and direction.

Explanation: Without direction, a vector is incomplete.

Q73. Give two examples of scalar quantities. 

Answer: Speed and mass.

Explanation: Both have magnitude only.

Q74. Give two examples of vector quantities. 

Answer: Force and velocity.

Explanation: Both require direction.

Q75. Why is velocity a vector quantity? 

Answer: Because it has magnitude and direction.

Explanation: Velocity describes speed in a given direction.

Q76. State one difference between speed and velocity. 

Answer: Speed has magnitude only, while velocity has magnitude and direction.

Explanation: Direction makes velocity a vector.

Q77. Is mass a scalar or vector? Give a reason. 

Answer: Mass is a scalar because it has magnitude only.

Explanation: It does not depend on direction.

Q78. Why is weight a vector? 

Answer: Because weight is a force and always acts downward.

Explanation: It has both magnitude and direction.

Q79. What is the direction of gravitational field strength near Earth? 

Answer: Toward the centre of the Earth (downward).

Q80. What is meant by resultant force? 

Answer: The single force that has the same effect as all the forces acting together.

Explanation: It is found by adding vectors.

Q81. Two forces act in the same direction. How are they combined? 

Answer: They are added together.

Q82. Two forces act in opposite directions. How are they combined? 

Answer: Subtract the smaller magnitude from the larger.

Explanation: Direction of larger force remains.

Q83. A car travels 100 m north. Is this distance or displacement? 

Answer: Displacement.

Explanation: Direction (north) is given.

Q84. A car travels 100 m. Is this distance or displacement? 

Answer: Distance.

Explanation: No direction is given.

Q85. Which quantity can change even if speed remains constant? 

Answer: Velocity.

Explanation: Velocity changes if direction changes.

Q86. What happens to velocity when an object moves in a circle at constant speed? 

Answer: Its direction changes continuously.

Explanation: Therefore velocity changes.

Q87. Define momentum. 

Answer: Momentum = mass × velocity.

Explanation: Since velocity is vector, momentum is vector.

Q88. Why is acceleration a vector quantity?

Answer: Because it describes change in velocity, which includes direction.

Q89. Give one example of a scalar quantity used in daily life. 

Answer: Temperature.

Q90. Give one example of a vector quantity used in daily life. 

Answer: Wind velocity.

Q91. What is required to fully describe a vector quantity? 

Answer: Magnitude and direction.

Q92. What is required to fully describe a scalar quantity? 

Answer: Magnitude only.

Q93. Which is a vector: energy or force? 

Answer: Force.

Q94. Which is scalar: displacement or distance? 

Answer: Distance.

Q95. If the resultant force on an object is zero, what can be said about motion? 

Answer: The object is either at rest or moving at constant velocity.

Explanation: Balanced forces mean no acceleration.

Q96. State one example of a vector field. 

Answer: Electric field strength.

Q97. Why is electric field strength a vector? 

Answer: It has magnitude and direction of force on a positive charge.

Q98. Define displacement. 

Answer: The shortest distance from initial to final position in a given direction.

Q99. Can displacement be zero even if distance is not zero? Explain. 

Answer: Yes.

Explanation: If an object returns to its starting point, displacement is zero.

Q100. What symbol is commonly used to represent vector quantities in diagrams? 

Answer: An arrow.

Explanation: Arrow length shows magnitude and arrow direction shows direction.

Q101. Define a scalar quantity. 

Answer: A scalar quantity has magnitude only and no direction.

Q102. Define a vector quantity. 

Answer: A vector quantity has both magnitude and direction.

Q103. Give two examples of scalar quantities. 

Answer: Speed and mass.

Q104. Give two examples of vector quantities. 

Answer: Force and velocity.

Q105. Why is speed a scalar quantity? 

Answer: Because it has magnitude only and no direction.

Q106. Why is velocity a vector quantity? 

Answer: Because it includes both magnitude and direction.

Q107. State one difference between distance and displacement. 

Answer: Distance is scalar, while displacement includes direction and is vector.

Q108. State one difference between mass and weight.

Answer: Mass is scalar, while weight is a vector force acting downward.

Q109. What is meant by resultant force? 

Answer: The single force that has the same effect as all the forces acting together.

Q110. How are scalar quantities added? 

Answer: They are added using normal arithmetic.

Q111. How are vectors acting in opposite directions combined? 

Answer: Subtract the smaller magnitude from the larger and keep the direction of the larger.

Q112. What is the unit of force? 

Answer: Newton (N).

Q113. Why is acceleration a vector quantity? 

Answer: Because it describes change in velocity, which includes direction.

Q114. What happens to velocity in circular motion at constant speed? 

Answer: Its direction changes continuously.

Q115. Give one example of a vector field. 

Answer: Electric field strength.

Q116. Why is momentum a vector quantity? 

Answer: Because momentum depends on velocity, which has direction.

Q117. State the formula for momentum. 

Answer: Momentum = mass × velocity.

Q118. Which quantity can be zero even when distance is not zero? 

Answer: Displacement.

Q119. What does the length of an arrow in a vector diagram represent? 

Answer: Magnitude.

Q120. What does the direction of an arrow in a vector diagram represent? 

Answer: Direction of the quantity.

Q121. Give one scalar quantity related to motion. 

Answer: Speed.

Q122. Give one vector quantity related to motion. 

Answer: Velocity.

Q123. If two equal forces act in opposite directions, what is the resultant? 

Answer: Zero.

Q124. Why must direction be included when stating velocity? 

Answer: Because without direction, it becomes speed, which is scalar.

Q125. State one similarity between scalars and vectors. 

Answer: Both have magnitude.

Q126. State the formula for the resultant of two perpendicular vectors. 

Answer: Resultant = √(A² + B²)

Q127. Which mathematical theorem is used to find the resultant of two perpendicular vectors? 

Answer: Pythagoras’ theorem.

Q128. What condition must be satisfied to use Pythagoras’ theorem for vectors? 

Answer: The two vectors must act at right angles (90°) to each other.

Q129. What does the hypotenuse of a right angled vector triangle represent? 

Answer: The resultant vector.

Q130. Two forces of 3 N and 4 N act at right angles. What is the resultant? 

Answer: 5 N.

Q131. Why cannot you directly add 3 N and 4 N to get 7 N when they are perpendicular? 

Answer: Because direction must be considered and vector rules must be used.

Q132. Write the formula used to calculate the direction of the resultant. 

Answer: tan θ = opposite ÷ adjacent.

Q133. What does the angle θ represent in vector problems? 

Answer: The direction of the resultant vector relative to one component.

Q134. If one perpendicular component is 6 N and the other is 8 N, what is the resultant? 

Answer: 10 N.

Q135. Two perpendicular velocities are 5 m/s and 12 m/s. What is the resultant speed? 

Answer: 13 m/s.

Q136. When finding resultant using Pythagoras, what is the final step? 

Answer: Take the square root.

Q137. In vector addition diagrams, what does arrow length represent? 

Answer: Magnitude.

Q138. In vector addition diagrams, what does arrow direction represent? 

Answer: Direction of the quantity.

Q139. If tan θ = 4/3, what does this ratio represent? 

Answer: The ratio of the perpendicular component to the horizontal component.

Q140. What unit is used for resultant force? 

Answer: Newton (N).

Q141. What unit is used for resultant velocity? 

Answer: Metres per second (m/s).

Q142. Why must the direction be included when stating a resultant vector? 

Answer: Because vectors require both magnitude and direction to be complete.

Q143. If two equal forces act at right angles, how does the resultant compare to one force? 

Answer: It equals one force multiplied by √2.

Q144. A boat moves east while river flows north. Why is Pythagoras used? 

Answer: Because the velocities are perpendicular.

Q145. What happens if two perpendicular vectors are both zero? 

Answer: The resultant is zero.

Q146. If resultant force is zero, what does this mean about motion? 

Answer: The object is at rest or moving at constant velocity.

Q147. State one real life example of perpendicular vectors. 

Answer: A plane flying in crosswind.

Q148. Why is vector addition important in force problems? 

Answer: Because forces have direction and must be combined correctly.

Q149. What shape is formed when adding two perpendicular vectors? 

Answer: A right angled triangle.

Q150. If two perpendicular forces are 9 N and 12 N, what is the resultant? 

Answer: 15 N.

Thank You!

Sana Shariq

For revision visit

https://youtu.be/LmnpKQv4_ys