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Physical Quantities and Measurement MCQs — Physics (page 3)

121 multiple-choice questions on Physical Quantities and Measurement from Physics, each with the correct answer and, where available, a teacher's explanation. Read through them to revise the chapter, then practise the same questions one by one to test yourself.

51. Which is the most reasonable estimate of the power of a household electric kettle?

  1. 2 MW
  2. 2 kW
  3. 200 kW
  4. 2 W

Answer: B) 2 kW

Explanation: A sensible order of magnitude for the power of a household electric kettle is 2 kW. SLO P-11-A-01 · Understanding

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52. Random errors can be reduced by:

  1. using a calibrated scale only once
  2. correcting the zero error
  3. taking many readings and averaging
  4. changing the unit

Answer: C) taking many readings and averaging

Explanation: Averaging cancels random scatter. SLO P-11-A-05 · Application

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53. The kinetic energy of a body depends on m and v: E = km^av^b. Then

  1. a = 1, b = 2
  2. a = 1, b = 1
  3. a = 12, b = 2
  4. a = 2, b = 1

Answer: A) a = 1, b = 2

Explanation: ML^2T^-2 = M^a( LT^-1)^b: a = 1, b = 2 (k = 12 cannot be found by dimensions). SLO P-11-A-04 · Application

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54. Accuracy of a measurement describes:

  1. how close repeated readings are to each other
  2. how many decimal places it has
  3. how close it is to the true value
  4. the smallest division of the scale

Answer: C) how close it is to the true value

Explanation: Accuracy is about closeness to the true value (systematic error). SLO P-11-A-05 · Application

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55. Readings of time for 20 oscillations: 31.2 s, 31.4 s, 31.3 s. The best value of the period is:

  1. 31.3 s
  2. 0.313 s
  3. 3.13 s
  4. 1.565 s

Answer: D) 1.565 s

Explanation: Mean = 31.3 s for 20 oscillations, so T = 31.3 / 20 = 1.565 s. SLO P-11-A-05 · Application

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56. The dimensions of force are:

  1. [ M L^2 T^-1]
  2. [ M L T^-2]
  3. [ M L^2 T^-2]
  4. [ M L T^-1]

Answer: B) [ M L T^-2]

Explanation: Write force in terms of mass, length and time: [ M L T^-2]. SLO P-11-A-03 · Application

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57. The dimensions of work are:

  1. [ M L^2 T^-2]
  2. [ M L T^-2]
  3. [ M L^2 T^-3]
  4. [ T^-1]

Answer: A) [ M L^2 T^-2]

Explanation: Write work in terms of mass, length and time: [ M L^2 T^-2]. SLO P-11-A-03 · Application

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58. Which is the most reasonable estimate of the speed of sound in air?

  1. 3 10^8 m/s
  2. 34 m/s
  3. 340 m/s
  4. 3400 m/s

Answer: C) 340 m/s

Explanation: A sensible order of magnitude for the speed of sound in air is 340 m/s. SLO P-11-A-01 · Understanding

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59. A rod's true length is 50.0 cm. Four students measure it five times each. Which set is both accurate and precise?

  1. 50.1, 49.9, 50.0, 50.1, 49.9 cm
  2. 52.1, 52.2, 52.1, 52.0, 52.1 cm
  3. 47.0, 53.5, 49.0, 51.8, 48.6 cm
  4. 45.2, 55.0, 52.3, 47.9, 54.1 cm

Answer: A) 50.1, 49.9, 50.0, 50.1, 49.9 cm

Explanation: The values are close to each other (precise) and their mean is close to 50.0 cm (accurate). SLO P-11-A-05 · Application

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60. Systematic errors cannot be reduced by:

  1. improving the method
  2. averaging repeated readings
  3. correcting zero error
  4. calibrating the instrument

Answer: B) averaging repeated readings

Explanation: All readings are shifted equally, so the average is shifted too. SLO P-11-A-05 · Application

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61. Two lengths are (25.4 pm 0.1) cm and (12.6 pm 0.1) cm. Their difference is:

  1. (12.8 pm 0.05) cm
  2. (12.8 pm 0.2) cm
  3. (12.8 pm 0) cm
  4. (38 pm 0.2) cm

Answer: B) (12.8 pm 0.2) cm

Explanation: For a sum or difference, add the absolute uncertainties. SLO P-11-A-06 · Application

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62. Reaction time adds uncertainty mainly to:

  1. the reading of a thermometer
  2. measurements of time with a hand-held stopwatch
  3. the mass of a block
  4. the length of a rod

Answer: B) measurements of time with a hand-held stopwatch

Explanation: Human reaction time is about 0.1–0.3 s. SLO P-11-A-07 · Understanding

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63. Which can dimensional analysis not find?

  1. whether an equation is homogeneous
  2. the dimensions of a constant such as G
  3. the value of a dimensionless constant such as 2pi
  4. the powers of the variables

Answer: C) the value of a dimensionless constant such as 2pi

Explanation: Pure numbers have no dimensions, so they cannot be found this way. SLO P-11-A-04 · Application

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64. A digital balance shows 25.38 g. The uncertainty is about:

  1. pm 0.1 g
  2. pm 0.01 g
  3. pm 1 g
  4. zero

Answer: B) pm 0.01 g

Explanation: The last digit shown is uncertain. SLO P-11-A-07 · Understanding

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65. The pressure p at depth h in a liquid depends on rho, g and h: p = krho^ag^bh^c. Then

  1. a = 1, b = 2, c = 1
  2. a = 1, b = 1, c = 2
  3. a = 2, b = 1, c = 1
  4. a = b = c = 1

Answer: D) a = b = c = 1

Explanation: M: a = 1; T: -2b = -2 Rightarrow b = 1; L: -3a + b + c = -1 Rightarrow c = 1: p = krho g h. SLO P-11-A-04 · Application

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66. The dimensions of power are:

  1. [ M L T^-2]
  2. [ L T^-2]
  3. [ M L^2 T^-3]
  4. [ M L^2 T^-2]

Answer: C) [ M L^2 T^-3]

Explanation: Write power in terms of mass, length and time: [ M L^2 T^-3]. SLO P-11-A-03 · Application

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67. Which is the most reasonable estimate of the radius of the Earth?

  1. 6.4 10^4 m
  2. 6.4 10^6 m
  3. 6.4 10^3 m
  4. 6.4 10^9 m

Answer: B) 6.4 10^6 m

Explanation: A sensible order of magnitude for the radius of the Earth is 6.4 10^6 m. SLO P-11-A-01 · Understanding

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68. A rod's true length is 50.0 cm. Readings 47.0, 53.5, 49.0, 51.8, 48.6 cm are:

  1. precise but not accurate
  2. neither — they are all equal
  3. both accurate and precise
  4. fairly accurate on average but not precise

Answer: D) fairly accurate on average but not precise

Explanation: Their mean (50.0 cm) is right, but they are widely scattered. SLO P-11-A-05 · Application

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69. Which is the most reasonable estimate of the time taken by light to reach the Earth from the Sun?

  1. 0.5 s
  2. 500 s (about 8 minutes)
  3. 50,000 s
  4. 5 s

Answer: B) 500 s (about 8 minutes)

Explanation: A sensible order of magnitude for the time taken by light to reach the Earth from the Sun is 500 s (about 8 minutes). SLO P-11-A-01 · Understanding

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70. How many significant figures are in 0.004050?

  1. 3
  2. 4
  3. 6
  4. 7

Answer: B) 4

Explanation: Leading zeros don't count; the trailing zero after 5 does: 4, 0, 5, 0. SLO P-11-A-07 · Understanding

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71. In R = V/I, the two measured quantities have uncertainties of pm0.2 in 20 and pm0.1 in 4. The percentage uncertainty in the result is:

  1. 1.5%
  2. 3.5%
  3. 1%
  4. 1.25%

Answer: B) 3.5%

Explanation: For a product or quotient, add the percentage uncertainties: 1% + 2.5% = 3.5%. SLO P-11-A-06 · Application

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72. The dimensions of frequency are:

  1. [ T^-1]
  2. [ L T^-2]
  3. [ M L^-1 T^-2]
  4. [ M L T^-1]

Answer: A) [ T^-1]

Explanation: Write frequency in terms of mass, length and time: [ T^-1]. SLO P-11-A-03 · Application

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73. Which is the most reasonable estimate of the mass of a mango?

  1. 3 kg
  2. 0.003 kg
  3. 0.3 kg
  4. 30 kg

Answer: C) 0.3 kg

Explanation: A sensible order of magnitude for the mass of a mango is 0.3 kg. SLO P-11-A-01 · Understanding

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74. The SI base units of impulse are:

  1. kg,m,s^-2
  2. kg,m,s^-1
  3. m,s^-2
  4. s^-1

Answer: B) kg,m,s^-1

Explanation: Impulse = FDelta t: N s = kg m s^-1, the same as momentum. SLO P-11-A-02 · Understanding

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75. The constant k in Hooke's law F = kx has dimensions:

  1. [ M L T^-2]
  2. [ M L^2 T^-2]
  3. [ L T^-2]
  4. [ M T^-2]

Answer: D) [ M T^-2]

Explanation: k = F/x: MLT^-2/L = MT^-2. SLO P-11-A-04 · Application

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