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Physical Quantities and Measurement MCQs — Physics

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.

1. The uncertainty of a single reading on a metre rule (smallest division 1 mm) is usually taken as:

  1. pm 1 mm (or pm 0.5 mm per end)
  2. pm 1 cm
  3. zero
  4. pm 0.01 mm

Answer: A) pm 1 mm (or pm 0.5 mm per end)

Explanation: It is limited by the smallest division of the scale. SLO P-11-A-07 · Understanding

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2. Every measurement contains some uncertainty because:

  1. SI units are not exact
  2. instruments have a limited resolution and readings involve judgement
  3. scientists make careless mistakes
  4. the true value always changes

Answer: B) instruments have a limited resolution and readings involve judgement

Explanation: Even a perfect method is limited by the smallest scale division and by random effects. SLO P-11-A-07 · Understanding

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3. Which is the most reasonable estimate of the mass of an electron?

  1. 9.1 10^-31 kg
  2. 1.67 10^-27 kg
  3. 9.1 10^-41 kg
  4. 9.1 10^-21 kg

Answer: A) 9.1 10^-31 kg

Explanation: A sensible order of magnitude for the mass of an electron is 9.1 10^-31 kg. SLO P-11-A-01 · Understanding

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4. Two lengths are (8.2 pm 0.05) cm and (3.15 pm 0.05) cm. Their difference is:

  1. (11.35 pm 0.1) cm
  2. (5.05 pm 0.1) cm
  3. (5.05 pm 0.025) cm
  4. (5.05 pm 0) cm

Answer: B) (5.05 pm 0.1) cm

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

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5. Is the equation F = mv^2r dimensionally correct (homogeneous)?

  1. No
  2. Yes
  3. Only if the constants are dimensionless
  4. It cannot be checked by dimensions

Answer: B) Yes

Explanation: mv^2/r: M L^2T^-2/L = MLT^-2. SLO P-11-A-03 · Application

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6. Which is the most reasonable estimate of the wavelength of visible light?

  1. 500 mm
  2. 5 m
  3. 500 pm
  4. 500 nm

Answer: D) 500 nm

Explanation: A sensible order of magnitude for the wavelength of visible light is 500 nm. SLO P-11-A-01 · Understanding

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7. The tesla (T) expressed in SI base units is:

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

Answer: C) kg,s^-2,A^-1

Explanation: B = F/(IL): N A^-1 m^-1 = kg s^-2 A^-1. SLO P-11-A-02 · Understanding

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8. The percentage uncertainty in the measured quantity is 1%. For A = pi r^2 the percentage uncertainty is:

  1. 0.5%
  2. 3%
  3. 2%
  4. 1%

Answer: C) 2%

Explanation: A quantity raised to the power 2 has 2 times the percentage uncertainty: 2 1% = 2%. SLO P-11-A-06 · Application

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9. The percentage uncertainty in the measured quantity is 2%. For Ek = 12mv^2 ( only v uncertain) the percentage uncertainty is:

  1. 6%
  2. 2%
  3. 4%
  4. 1%

Answer: C) 4%

Explanation: A quantity raised to the power 2 has 2 times the percentage uncertainty: 2 2% = 4%. SLO P-11-A-06 · Application

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10. An ammeter reads 0.05 A with no current. This is:

  1. a parallax error
  2. human reaction error
  3. a random error
  4. a zero error

Answer: D) a zero error

Explanation: The instrument does not read zero when it should. SLO P-11-A-05 · Application

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11. Measured values are given with a sensible number of significant figures because:

  1. calculators require it
  2. it removes uncertainty
  3. more figures are always better
  4. the number of figures shows the precision of the measurement

Answer: D) the number of figures shows the precision of the measurement

Explanation: Extra digits would claim a precision that wasn't achieved. SLO P-11-A-07 · Understanding

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12. Two masses are (12 pm 0.3) kg and (5 pm 0.2) kg. Their total mass is:

  1. (17 pm 0.06) kg
  2. (7 pm 0.5) kg
  3. (17 pm 0.5) kg
  4. (17 pm 0.3) kg

Answer: C) (17 pm 0.5) kg

Explanation: Absolute uncertainties add. SLO P-11-A-06 · Application

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13. Is the equation v = u + at dimensionally correct (homogeneous)?

  1. It cannot be checked by dimensions
  2. No
  3. Yes
  4. Only if the constants are dimensionless

Answer: C) Yes

Explanation: Each term has dimensions [ LT^-1] (at: LT^-2 T). SLO P-11-A-03 · Application

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14. The SI base units of the spring constant k are:

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

Answer: D) kg,s^-2

Explanation: k = F/x: N m^-1 = kg s^-2. SLO P-11-A-02 · Understanding

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15. In P = VI, the two measured quantities have uncertainties of pm0.1 in 5 and pm0.04 in 2. The percentage uncertainty in the result is:

  1. 6%
  2. 5%
  3. 2%
  4. 4%

Answer: D) 4%

Explanation: For a product or quotient, add the percentage uncertainties: 2% + 2% = 4%. SLO P-11-A-06 · Application

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16. The result of 4.52 2.1 should be given as:

  1. 9.492
  2. 9.5
  3. 9
  4. 9.49

Answer: B) 9.5

Explanation: Keep the smallest number of significant figures (2). SLO P-11-A-07 · Understanding

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17. A reading is (12.5 pm 0.25). Its fractional uncertainty is:

  1. 0.25
  2. 50
  3. 2
  4. 0.02

Answer: D) 0.02

Explanation: Fractional uncertainty = 0.2512.5 = 0.02 (that is 2%). SLO P-11-A-06 · Application

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18. A zero error in a micrometer screw gauge causes:

  1. no error at all
  2. a random error that affects precision
  3. an error only in repeated readings
  4. a systematic error that affects accuracy

Answer: D) a systematic error that affects accuracy

Explanation: Every reading is shifted by the same amount. SLO P-11-A-05 · Application

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19. Which is the most reasonable estimate of the mass of an adult person?

  1. 7 kg
  2. 700 kg
  3. 70 kg
  4. 7000 kg

Answer: C) 70 kg

Explanation: A sensible order of magnitude for the mass of an adult person is 70 kg. SLO P-11-A-01 · Understanding

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20. A reading is (80 pm 2). Its fractional uncertainty is:

  1. 2.5
  2. 40
  3. 2
  4. 0.025

Answer: D) 0.025

Explanation: Fractional uncertainty = 280 = 0.025 (that is 2.5%). SLO P-11-A-06 · Application

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21. Dimensional analysis fails to derive a formula that contains:

  1. a single constant
  2. only products of powers
  3. a sum of terms or trigonometric/exponential functions
  4. mass, length and time

Answer: C) a sum of terms or trigonometric/exponential functions

Explanation: The method assumes the quantity is a product of powers of the variables. SLO P-11-A-04 · Application

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22. The percentage uncertainty in measuring 2.0 mm with a ruler of resolution 1 mm is large because:

  1. the uncertainty is a large fraction of a small reading
  2. the ruler is broken
  3. small lengths can't be measured
  4. mm is not an SI unit

Answer: A) the uncertainty is a large fraction of a small reading

Explanation: 12 100% = 50% — use a more precise instrument. SLO P-11-A-07 · Understanding

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23. The watt (W) expressed in SI base units is:

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

Answer: A) kg,m^2,s^-3

Explanation: P = W/t: J s^-1 = kg m^2 s^-3. SLO P-11-A-02 · Understanding

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24. Parallax error when reading a scale is avoided by:

  1. keeping the eye perpendicular to the scale
  2. taking only one reading
  3. using a longer scale
  4. reading quickly

Answer: A) keeping the eye perpendicular to the scale

Explanation: Viewing at an angle shifts the apparent reading. SLO P-11-A-05 · Application

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25. Which is the most reasonable estimate of the diameter of an atom?

  1. 10^-10 m
  2. 10^-15 m
  3. 10^-2 m
  4. 10^-5 m

Answer: A) 10^-10 m

Explanation: A sensible order of magnitude for the diameter of an atom is 10^-10 m. SLO P-11-A-01 · Understanding

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