Gas Laws: JAMB Physics Questions, Answers & Notes

What Gas Laws covers in the JAMB Physics syllabus

The gas laws describe a fixed mass of gas (always use kelvin for T). Boyle's law: at constant temperature P ∝ 1/V (PV = constant). Charles's law: at constant pressure V ∝ T (V/T = constant). The pressure law: at constant volume P ∝ T (P/T = constant). Combined: PV/T = constant. Standard temperature and pressure (s.t.p.) is 0 °C and 1 atmosphere. Kinetic theory explains gas pressure as molecules colliding with the container walls. Real gases behave most ideally at low pressure and high temperature.

For Gas Laws, JAMB expects you to be able to:

• State and apply Boyle's, Charles's and the pressure law
• Use the combined gas equation PV/T = constant with kelvin temperatures
• Relate the gas laws to kinetic theory and ideal gas behaviour

Key facts & revision notes: Gas Laws

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

• Boyle's law: at constant temperature, P ∝ 1/V, so PV = constant.
• Charles's law: at constant pressure, V ∝ T (absolute temperature), so V/T = constant.
• Boyle's law: P₁V₁ = P₂V₂ → 100 × 200 = 200 × V₂ → V₂ = 100 cm³.
• At constant volume, P ∝ T (absolute temperature), so P/T = constant.
• The combined gas law: PV/T = constant for a fixed mass of gas.
• Gas laws require absolute temperature, measured in kelvin.
• Charles's law: V₁/T₁ = V₂/T₂ → 300/300 = V₂/600 → V₂ = 600 cm³.
• Since P ∝ 1/V (Boyle's law), a graph of P against 1/V is a straight line through the origin.
• is 0 °C (273 K) and 1 atmosphere (about 76 cmHg).
• Convert to K: 300 K and 400 K.
• P/T constant → ratio = 400/300 = 4/3, i.e.
• Gas pressure results from countless molecular collisions with the walls of the container.
• V₁/T₁ = V₂/T₂ → 500/400 = V₂/200 → V₂ = 250 cm³.
• Compression at constant temperature (changing P and V) is governed by Boyle's law.
• P₁V₁ = P₂V₂ → 100 × 250 = 125 × V₂ → V₂ = 25000/125 = 200 cm³.
• An ideal gas is a theoretical gas that obeys the gas laws exactly under all conditions.
• Charles's law (V ∝ T) gives a straight line through the origin on a V–T (kelvin) graph.
• Extrapolating Charles's law, the volume would reach zero at absolute zero, 0 K.
• At low pressure and high temperature, molecules are far apart, so real gases behave nearly ideally.
• Using PV/T = constant: doubling P and T together leaves V unchanged.
• Charles's law relates V and T for a fixed mass of gas at constant pressure.
• Pressure is inversely proportional to volume at constant temperature.
• P₁V₁ = P₂V₂: 100 × 400 = 200 × V, so V = 200 cm³.
• V/T constant: 250/250 = V/500, so V = 500 cm³.

Worked examples

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

How Gas Laws is tested in JAMB Physics

Our Gas Laws bank holds 40 questions (1 easy, 26 medium, 13 hard). JAMB Physics typically returns to Gas Laws 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 Gas Laws 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 Gas Laws. 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 Gas Laws is repeated timed practice, so use the button above until the recurring patterns feel automatic.

Common mistakes to avoid in Gas Laws

The errors that cost marks on Gas Laws 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 Gas Laws actively by answering questions, not just by re-reading notes — recall under time is what the exam rewards.

Frequently asked questions

Is Gas Laws part of the JAMB Physics syllabus?

Yes. Gas Laws is a recognised topic in the JAMB Physics syllabus, covering state and apply Boyle's, Charles's and the pressure law. You should be able to recall its key facts and apply them to multiple-choice questions.

How many Gas Laws questions can I practise on Belmadeng?

There are 40 original, JAMB-standard Gas Laws 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 Gas Laws?

The gas laws describe a fixed mass of gas (always use kelvin for T). Boyle's law: at constant temperature P ∝ 1/V (PV = constant). Charles's law: at constant pressure V ∝ T (V/T = constant). The pressure law: at constant volume P ∝ T (P/T = constant). Combined: PV/T = constant. Standard temperature …

How do I answer Gas Laws questions quickly in JAMB?

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

Are these JAMB Physics Gas Laws 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 Gas Laws questions free without signing up?

Right here — tap “Start Gas Laws 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.