IGCSE Physics: Pressure Practice Questions
Pressure is the force acting per unit area, calculated as pressure = force divided by area and measured in pascals. In a liquid the pressure at a depth is given by p = rho g h and acts equally in all directions.
Sub-topic 1.8 of Cambridge IGCSE Physics 0625 has two equations and one common trap: converting square centimetres to square metres. The questions below use both equations and force the conversion explicitly.
What you need to know for Pressure
- Pressure equationp = F divided by A, with force in newtons and area in square metres, giving pressure in pascals. One pascal is one newton per square metre.
- Area conversion1 m2 = 10000 cm2. To convert cm2 to m2, divide by 10000, not by 100.
- Pressure in a liquidp = rho g h, where rho is the density of the liquid, g is the gravitational field strength and h is the depth below the surface. Pressure increases with depth and does not depend on the shape of the container.
- Pressure acts in all directionsAt a given depth in a fluid, pressure acts equally in every direction, which is why a diver feels pressure on all sides.
- ManometerA U-tube containing liquid used to measure the pressure difference between a gas supply and the atmosphere. The difference in the two levels gives the pressure difference.
- Gas pressure and the particle modelGas pressure results from particles colliding with the container walls. More frequent or more forceful collisions produce a higher pressure.
IGCSE Physics Pressure questions and answers
4 exam-style questions written to the 0625 syllabus. Try each one on paper first, then open the worked answer to check your method against the marks.
A box weighs 240 N and stands on a base measuring 40 cm by 30 cm. Calculate the pressure it exerts on the floor in pascals.
Show the worked answer
- Area = 40 x 30 = 1200 cm2.
- Convert to square metres by dividing by 10000: 1200 divided by 10000 = 0.12 m2.
- Use p = F divided by A = 240 divided by 0.12.
- Pressure = 2000 Pa, which is 2000 N/m2.
Calculate the pressure due to the water at a depth of 15 m in a lake. The density of water is 1000 kg/m3 and g is 9.8 N/kg.
Show the worked answer
- Use p = rho g h.
- Substitute: p = 1000 x 9.8 x 15.
- p = 147000 Pa.
- This is the pressure due to the water alone. The total pressure on a diver also includes atmospheric pressure of about 100000 Pa acting on the surface.
Explain why the pressure in a liquid at a given depth is the same regardless of the shape or width of the container.
Show the worked answer
- The pressure at a point in a liquid is given by p = rho g h.
- The only variables in that expression are the density of the liquid, the gravitational field strength and the vertical depth below the surface.
- The width, shape and total volume of the container do not appear, so they have no effect on the pressure.
- This is why water rises to the same level in every arm of a set of connected tubes of different shapes.
Explain, in terms of particles, why the pressure of a fixed mass of gas increases when it is heated in a sealed container of constant volume.
Show the worked answer
- Heating increases the average kinetic energy of the gas particles, so they move faster.
- Faster particles reach the walls more often, so the number of collisions per second increases.
- Each collision also exerts a greater force, because the particles have greater momentum.
- Since the volume and therefore the wall area are fixed, a greater total force on the same area means a higher pressure.
Common mistakes in this topic
- Converting cm2 to m2 by dividing by 100.
- Using mass instead of weight as the force in p = F divided by A.
- Using a slant distance rather than the vertical depth in p = rho g h.
- Forgetting to add atmospheric pressure when a question asks for total pressure.
- Quoting pressure in newtons. The unit is the pascal, which is newtons per square metre.
Exam tips
- Convert every area to square metres before substituting, and show the conversion as a separate line.
- For a question about why something has a large or small area, link it directly to pressure: skis spread weight over a large area to reduce pressure, a knife blade concentrates force on a small area to increase it.
- In p = rho g h, h is always the vertical depth below the free surface.
- For manometer questions, the pressure difference comes from the difference in the two liquid levels, not from either level alone.
- Every gas pressure explanation needs collisions with the walls, their frequency and their force.
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Pressure FAQs
How do I calculate pressure?
Divide the force in newtons by the area in square metres, giving pressure in pascals. If the area is given in square centimetres, divide it by 10000 first, because one square metre contains 10000 square centimetres.
How does pressure change with depth in a liquid?
Pressure increases with depth according to p = rho g h, where rho is the liquid's density, g is gravitational field strength and h is the vertical depth below the surface. Pressure at a given depth acts equally in all directions and does not depend on the shape of the container.
Why does gas pressure increase when temperature rises?
Higher temperature gives the particles more kinetic energy, so they move faster. They collide with the container walls more frequently and each collision exerts a greater force. With the wall area unchanged, the greater total force means a higher pressure.
Why do skis stop you sinking into snow?
Pressure is force divided by area. Your weight stays the same on skis, but the area in contact with the snow is far larger, so the pressure on the snow is much smaller. The snow is therefore less likely to be compressed enough for you to sink in.
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Written to the published Cambridge IGCSE Physics (0625) syllabus. Check your school entry code and syllabus year, because Core and Extended candidates are assessed on different content. Last reviewed 2026-08-12.