A Level Physics 14.2 Temperature Scales MCQs – 30 Practice Questions with Answers (Cambridge 9702)
This page covers Section 14.2, Temperature Scales, from the Cambridge International AS & A Level Physics (9702) syllabus – an A Level (A2) topic. Work through 30 original multiple-choice questions on converting between the Celsius and kelvin scales, absolute zero and the thermodynamic scale, and how temperatures are measured in practice, each with a fully worked answer.
Formula recap: T / K = θ / °C + 273.15 (use 273 in calculations at this level). A temperature change of 1 K is exactly equal to a change of 1 °C. For the complete list of 9702 equations, see the A Level Physics Formula Sheet.
Celsius & Kelvin Scales
Q1. The ice point of water, 0 °C, expressed on the kelvin scale is
- (A) 0 K
- (B) 273 K
- (C) 100 K
- (D) −273 K
Show Answer
Answer: B – T = θ + 273 = 0 + 273 = 273 K. The kelvin scale starts at absolute zero, so everyday Celsius temperatures convert to kelvin values about 273 higher.
Q2. The steam point of water, 100 °C, expressed in kelvin is
- (A) 100 K
- (B) 173 K
- (C) 373 K
- (D) 473 K
Show Answer
Answer: C – T = 100 + 273 = 373 K. The interval between the ice point and the steam point is 100 K, exactly the same size as 100 °C.
Q3. A thermodynamic temperature of 300 K is equal to
- (A) 27 °C
- (B) 573 °C
- (C) −27 °C
- (D) 300 °C
Show Answer
Answer: A – θ = T − 273 = 300 − 273 = 27 °C. To convert from kelvin to Celsius, subtract 273.
Q4. On a very cold day the temperature is −40 °C. This temperature in kelvin is
- (A) 40 K
- (B) 313 K
- (C) −40 K
- (D) 233 K
Show Answer
Answer: D – T = −40 + 273 = 233 K. Negative Celsius temperatures are perfectly possible, but the kelvin value is still positive.
Q5. A liquid warms up from 20 °C to 45 °C. The rise in temperature expressed in kelvin is
- (A) 25 °C worth, so 298 K
- (B) 25 K
- (C) 65 K
- (D) 318 K
Show Answer
Answer: B – The rise is 45 − 20 = 25 Celsius degrees, and a change of 1 °C is exactly the same interval as a change of 1 K, so the rise is 25 K. Only the zero points of the two scales differ, not the size of the degree.
Q6. The lower fixed point used when setting up the Celsius scale is
- (A) the temperature of pure melting ice at standard atmospheric pressure
- (B) the temperature of a healthy human body
- (C) the lowest temperature reached in a freezer
- (D) the temperature at which water has its maximum density
Show Answer
Answer: A – The ice point – pure ice melting in equilibrium with water at standard atmospheric pressure – is defined as 0 °C. The upper fixed point, the steam point, is defined as 100 °C.
Q7. The upper fixed point of the Celsius scale, the steam point, is the temperature of
- (A) steam formed at any pressure
- (B) water boiling in an open beaker on a stove
- (C) the hottest part of a Bunsen flame
- (D) steam in equilibrium with boiling water at standard atmospheric pressure
Show Answer
Answer: D – The steam point is defined as 100 °C at standard atmospheric pressure (1.01 × 105 Pa). Because the boiling point of water depends on pressure, the pressure must be specified for the fixed point to be reproducible.
Q8. Which of the following temperatures is impossible?
- (A) −100 °C
- (B) 0 °C
- (C) −50 K
- (D) 10 K
Show Answer
Answer: C – The kelvin scale begins at absolute zero, 0 K, so a negative kelvin temperature cannot occur. Celsius temperatures can be negative because the Celsius zero is set at the ice point, well above absolute zero.
Q9. Room temperature, 25 °C, expressed in kelvin is
- (A) 298 K
- (B) 248 K
- (C) 25 K
- (D) 273 K
Show Answer
Answer: A – T = 25 + 273 = 298 K. This value, just under 300 K, is worth remembering as a typical room temperature on the thermodynamic scale.
Q10. A metal block cools from 80 °C to 30 °C. The fall in temperature expressed in kelvin is
- (A) 110 K
- (B) 50 K
- (C) 323 K
- (D) 223 K
Show Answer
Answer: B – The fall is 80 − 30 = 50 Celsius degrees. Temperature differences have the same numerical value on both scales, so the fall is 50 K. (323 K and 223 K are the two end temperatures converted individually – not the difference.)
Absolute Zero & the Thermodynamic Scale
Q11. Absolute zero, expressed on the Celsius scale, is
- (A) 0 °C
- (B) −100 °C
- (C) −273.15 °C
- (D) −373 °C
Show Answer
Answer: C – Absolute zero is 0 K, and using the exact conversion T / K = θ / °C + 273.15 gives θ = 0 − 273.15 = −273.15 °C. At this level, −273 °C is an acceptable approximation.
Q12. At absolute zero, the particles of a substance
- (A) have the minimum possible kinetic energy
- (B) stop existing as separate particles
- (C) all join together into a single solid block
- (D) move at their greatest possible speed
Show Answer
Answer: A – Absolute zero is the temperature at which the particles of a substance have the least possible kinetic energy, which is why no lower temperature can exist. Thermal energy cannot be removed below this minimum state.
Q13. The thermodynamic (kelvin) temperature scale is defined using two fixed points. These are
- (A) the ice point and the steam point of water
- (B) the freezing and boiling points of mercury
- (C) the melting point of ice and the temperature of the Sun
- (D) absolute zero and the triple point of water
Show Answer
Answer: D – The kelvin scale is fixed by absolute zero (0 K) and the triple point of water, which is assigned the value 273.16 K. One kelvin is 1/273.16 of the interval between these two points.
Q14. The triple point of water – the temperature at which ice, liquid water and water vapour coexist in equilibrium – has the value
- (A) 0 K
- (B) 273.16 K
- (C) 373.16 K
- (D) 100 K
Show Answer
Answer: B – The triple point of water is 273.16 K, which is 0.01 °C – very slightly above the ice point. It is used as a fixed point because, unlike the ice point, it does not depend on the surrounding pressure being exactly standard.
Q15. The SI base unit of temperature is the
- (A) kelvin
- (B) degree Celsius
- (C) degree Fahrenheit
- (D) joule
Show Answer
Answer: A – The kelvin (symbol K, with no degree sign) is the SI base unit of thermodynamic temperature. The degree Celsius is a derived unit of the same size, offset by 273.15.
Q16. An important advantage of the thermodynamic temperature scale is that it
- (A) gives larger numbers that are easier to plot
- (B) can only be measured with one particular thermometer
- (C) does not depend on the properties of any particular substance
- (D) never requires fixed points for its definition
Show Answer
Answer: C – Because the kelvin scale is anchored to absolute zero and the triple point of water, its values are the same whatever thermometric substance is used to measure them. Scales built on a single liquid’s expansion, by contrast, can disagree slightly with each other.
Q17. A gas is held in a sealed container at 20 °C. The gas is heated until its thermodynamic temperature has doubled. The final temperature of the gas is
- (A) 40 °C
- (B) 313 °C
- (C) 586 °C
- (D) 566 °C
Show Answer
Answer: B – First convert: 20 °C = 293 K. Doubling gives 586 K. Converting back: 586 − 273 = 313 °C. Doubling a Celsius temperature does NOT double the thermodynamic temperature – ratios only work on the kelvin scale, which starts at absolute zero.
Q18. Which statement about a temperature of 0 K is correct?
- (A) It is the temperature of melting ice
- (B) It can be reached easily with a good freezer
- (C) It is equal to 273 °C
- (D) It is the lowest temperature that can exist
Show Answer
Answer: D – 0 K is absolute zero, the lower limit of temperature. In practice it can be approached very closely but never quite reached, and temperatures below it are impossible.
Q19. The pressure of a fixed mass of gas at constant volume is directly proportional to its temperature, provided the temperature is measured
- (A) on the thermodynamic (kelvin) scale
- (B) on the Celsius scale
- (C) on any scale with an arbitrary zero
- (D) in degrees Fahrenheit
Show Answer
Answer: A – Gas-law proportionalities such as p ∝ T only hold when T is measured from absolute zero. On the Celsius scale, a gas at 0 °C would wrongly appear to have zero pressure; in kelvin it is at 273 K, with plenty of molecular motion remaining.
Q20. The mean kinetic energy of the molecules of an ideal gas is directly proportional to
- (A) the Celsius temperature of the gas
- (B) the square of the Celsius temperature
- (C) the thermodynamic temperature of the gas
- (D) the pressure alone, whatever the temperature
Show Answer
Answer: C – Kinetic theory gives mean molecular kinetic energy ∝ T, where T is in kelvin. This is the deep reason the thermodynamic scale is the natural one for physics: it is zero exactly when the molecular kinetic energy is at its minimum.
Measuring Temperature
Q21. A physical property used to measure temperature – a thermometric property – must
- (A) be a property of water only
- (B) stay constant as the temperature changes
- (C) change only when the temperature reaches a fixed point
- (D) vary continuously with temperature, and ideally vary linearly
Show Answer
Answer: D – A useful thermometric property (such as the length of a liquid thread or the resistance of a wire) must change smoothly and continuously as temperature changes, so that each value of the property corresponds to one temperature. A linear variation makes calibration and reading simplest.
Q22. In a liquid-in-glass thermometer, the thermometric property is
- (A) the colour of the liquid
- (B) the length of the liquid thread in the capillary tube
- (C) the mass of liquid in the bulb
- (D) the pressure inside the sealed tube
Show Answer
Answer: B – As the temperature rises, the liquid expands more than the glass and the thread lengthens along the capillary. The length of the thread is the measurable property that is calibrated against the fixed points.
Q23. In a thermocouple thermometer, the thermometric property is the
- (A) e.m.f. produced at the junction of two different metals
- (B) resistance of a coil of platinum wire
- (C) expansion of a gas at constant pressure
- (D) colour of light emitted by a glowing filament
Show Answer
Answer: A – When the junction of two different metal wires is at a different temperature from the reference junction, a small e.m.f. is generated that depends on the temperature difference. A voltmeter measuring this e.m.f. acts as the thermometer.
Q24. A thermocouple is particularly suitable for measuring a temperature that changes rapidly because
- (A) it contains a large bulb of liquid that stores heat
- (B) it can only be read once per minute
- (C) its junction is very small, so it responds almost immediately
- (D) it does not need to be placed in contact with the object
Show Answer
Answer: C – The measuring junction of a thermocouple has a tiny thermal capacity, so it reaches the temperature of its surroundings very quickly. This makes it ideal for rapidly changing temperatures and for measuring the temperature at a point.
Q25. In a platinum resistance thermometer, temperature is measured from changes in the
- (A) length of the platinum wire
- (B) colour of the platinum wire
- (C) mass of the platinum wire
- (D) electrical resistance of the platinum wire
Show Answer
Answer: D – The resistance of a metal wire increases steadily as its temperature rises. Measuring the resistance of the platinum coil (often with a bridge circuit) gives an accurate, repeatable temperature reading over a wide range.
Q26. Two thermometers based on different thermometric properties agree exactly at the two fixed points used to calibrate them, but may disagree slightly at temperatures in between. This is because
- (A) one of the thermometers must be faulty
- (B) the two properties do not vary with temperature in exactly the same way
- (C) fixed points cannot be reproduced accurately
- (D) all thermometric properties vary randomly with temperature
Show Answer
Answer: B – Each scale assumes its own property varies linearly between the fixed points, but different properties (for example, the expansion of mercury and the resistance of platinum) do not keep in perfect step. The readings therefore agree at the fixed points but can differ slightly elsewhere; the thermodynamic scale avoids this by definition.
Q27. In a constant-volume gas thermometer, the thermometric property is
- (A) the volume of the gas
- (B) the density of the gas
- (C) the pressure of the gas
- (D) the speed of sound in the gas
Show Answer
Answer: C – The gas is kept at constant volume, and its pressure rises in direct proportion to the thermodynamic temperature. Gas thermometers of this type are very accurate and are used to calibrate other thermometers.
Q28. Which is an advantage of a thermocouple thermometer compared with a liquid-in-glass thermometer?
- (A) It can measure over a very wide range of temperatures
- (B) It needs no electrical equipment of any kind
- (C) Its reading never depends on a reference junction
- (D) It works by the expansion of a liquid
Show Answer
Answer: A – Thermocouples can be made from metals that survive very high temperatures, giving a range far wider than a liquid-in-glass thermometer. They also give an electrical output that can be recorded automatically or fed to a data logger.
Q29. To set up a Celsius scale on an unmarked liquid-in-glass thermometer, the bulb is placed first in melting ice and then in steam at standard pressure. The length of the thread is marked in each case. The interval between the two marks is then
- (A) divided into 273 equal parts
- (B) divided into 10 equal parts
- (C) left undivided, since only the fixed points can be known
- (D) divided into 100 equal parts, each part being one Celsius degree
Show Answer
Answer: D – The ice point is marked 0 °C and the steam point 100 °C. Dividing the fundamental interval into 100 equal parts gives the Celsius scale, assuming the expansion of the liquid is uniform.
Q30. The density of water would be a poor thermometric property near 4 °C because
- (A) water has no density at 4 °C
- (B) the density does not vary monotonically with temperature – it is a maximum at 4 °C, so one density value corresponds to two different temperatures
- (C) density can only be measured at the fixed points
- (D) the density of water changes far too quickly to measure
Show Answer
Answer: B – Water contracts as it warms from 0 °C to 4 °C and expands above 4 °C, so its density passes through a maximum at 4 °C. A thermometric property must give one value for each temperature; a property that increases and then decreases cannot do this.
Keep practising: find more board-wise physics questions, organised by syllabus section, on the Physics MCQs hub, and keep the A Level Physics Formula Sheet open beside you while you revise Topic 14.
These are original practice questions written for revision purposes only. They are not Cambridge past-paper questions, and this page is not affiliated with or endorsed by Cambridge Assessment International Education.