Vapours: JAMB Physics Questions, Answers & Notes

What Vapours covers in the JAMB Physics syllabus

A vapour is a gas below its critical temperature, so it can be liquefied by pressure alone. Saturated vapour pressure (SVP), the pressure of a vapour in equilibrium with its liquid, depends only on temperature and rises with it. A liquid boils when its SVP equals the external pressure — so water boils cooler at altitude (lower pressure) and hotter in a pressure cooker. Humidity is the water vapour in air; relative humidity is a percentage, and the dew point is the temperature at which air saturates and dew/mist/fog forms by condensation. A hygrometer measures humidity.

For Vapours, JAMB expects you to be able to:

• Define vapour, saturated vapour pressure and critical temperature
• Relate SVP to boiling and the effect of pressure and altitude
• Explain humidity, dew point, and condensation phenomena

Key facts & revision notes: Vapours

These are the recurring points our Vapours questions test — revise them until each feels automatic, then practise the questions above to lock them in.

• A vapour is a gas below its critical temperature, so it can be liquefied by pressure alone.
• Saturated vapour pressure (SVP) is the pressure of a vapour in equilibrium with its liquid.
• Boiling occurs when the SVP of the liquid equals the surrounding atmospheric pressure.
• SVP depends only on temperature (it rises with temperature), not on volume or surface area.
• Lower atmospheric pressure means SVP equals it at a lower temperature, so water boils cooler.
• Humidity describes the water vapour content of the air.
• The dew point is the temperature at which air becomes saturated and condensation (dew) starts.
• Relative humidity is given as a percentage of the maximum vapour the air could hold at that temperature.
• An unsaturated vapour is not in equilibrium with its liquid and can accept more vapour.
• At night the ground cools below the dew point, so water vapour in the air condenses as dew.
• Higher pressure raises the boiling point, so water and food reach higher temperatures.
• A hygrometer measures the humidity of the air.
• SVP increases with rising temperature.
• Cooling warm moist air below its dew point condenses vapour into tiny droplets, forming mist or fog.
• Raising the external pressure means the SVP must reach a higher value, so the boiling point rises.
• Cooling a vapour or compressing it (below its critical temperature) causes it to condense.
• Heat, dry (low-humidity) air and wind all speed up evaporation, so clothes dry faster.
• Above its critical temperature, a gas cannot be liquefied by pressure alone, however great.
• Air holding the maximum possible water vapour at a temperature is saturated.
• The cold glass cools nearby air below its dew point, condensing vapour on the outer surface.
• Such a gas is called a vapour.
• Boiling begins when the saturated vapour pressure equals the external pressure.
• Relative humidity is measured at the current temperature.
• The cold surface cools nearby air below its dew point, so vapour condenses.

Worked examples

Three Vapours questions with the answer and a short explanation, so you can see how the topic is set before you practise the full set.

How Vapours is tested in JAMB Physics

Our Vapours bank holds 40 questions (4 easy, 29 medium, 7 hard). JAMB Physics typically returns to Vapours year after year, so steady practice on this topic is high-value revision. Questions are multiple-choice with four options, and at UTME pace you get roughly 40 seconds each — which is why timed practice matters.

How to answer Vapours questions

Work the stem first and predict the answer before you look at the options; then eliminate the ones that contradict the key facts above. Watch for “which is not…”, “all of the above” and “except” style stems, which are where rushed candidates lose easy marks on Vapours. If a calculation or a precise definition is involved, work it from first principles rather than guessing from a half-remembered rule. When two options look right, re-read the stem for the qualifier that separates them — JAMB rarely repeats an option by accident. If you are still unsure, eliminate the two weakest choices to lift your odds, flag the question, and move on; never burn a full minute on one Physics item when the exam gives you about forty seconds each. Then come back to flagged questions with whatever time remains. The single most reliable way to get faster at Vapours is repeated timed practice, so use the button above until the recurring patterns feel automatic.

Common mistakes to avoid in Vapours

The errors that cost marks on Vapours are usually careless rather than conceptual: misreading a negative stem, confusing two similar terms, or rushing a definition you actually know. Candidates also over-rely on “expo” and last-minute cramming instead of understanding the topic — which fails the moment JAMB rephrases a familiar idea. Treat every option as a claim to be checked against the facts above, keep your working tidy for any calculation, and don’t change a considered answer on a hunch. Above all, revise Vapours actively by answering questions, not just by re-reading notes — recall under time is what the exam rewards.

Frequently asked questions

Is Vapours part of the JAMB Physics syllabus?

Yes. Vapours is a recognised topic in the JAMB Physics syllabus, covering define vapour, saturated vapour pressure and critical temperature. You should be able to recall its key facts and apply them to multiple-choice questions.

How many Vapours questions can I practise on Belmadeng?

There are 40 original, JAMB-standard Vapours questions in our free bank, each with the correct answer and a worked explanation. You can practise them untimed or as a timed test.

What are the most important points to know about Vapours?

A vapour is a gas below its critical temperature, so it can be liquefied by pressure alone. Saturated vapour pressure (SVP), the pressure of a vapour in equilibrium with its liquid, depends only on temperature and rises with it. A liquid boils when its SVP equals the external pressure — so water boi…

How do I answer Vapours questions quickly in JAMB?

Read the stem carefully, eliminate clearly wrong options, and match the remaining choices to the key facts for Vapours. Practising timed Vapours questions builds the speed you need for UTME's pace of about 40 seconds per question.

Are these JAMB Physics Vapours questions past questions or original?

They are original questions written to JAMB (UTME) standard and mapped to the official syllabus — not reproduced past papers. This keeps them legal to use freely while closely mirroring how the real exam tests the topic.

Where can I practise Vapours questions free without signing up?

Right here — tap “Start Vapours practice” on this page to begin instantly. Belmadeng's CBT practice is completely free and needs no sign-up, download or subscription.

About these questions: original, JAMB-standard items written from the official UTME Physics syllabus (last reviewed 2026-09-18). Belmadeng is an independent study platform and is not affiliated with JAMB. Spotted an error? Use the report link.