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O-Level Pressure
What the O-Level syllabus expects for Pressure, and how to practise it.
What the syllabus expects
- Define pressure using force and area.
- Recall and use pressure = force / area in unfamiliar situations or problem solving.
- Describe and account for how pressure is transmitted in hydraulic systems, particularly the hydraulic press.
- Recall and use density = mass / volume in unfamiliar situations or problem solving.
- Describe using the height of a liquid column to measure atmospheric pressure.
- Describe how a manometer measures a pressure difference.
How it's examined
Questions on this topic most often ask you to find, calculate, explain, identify. About 8% of the past-paper style questions in Rae's bank for this subject sit in this topic.
Worked examples
Example 1 (2 marks)
(c) Explain why the pressure has the same value at every point on the inner walls of the syringe.
Show the worked answer
The syringe contains a gas whose particles are in constant, rapid, random motion, colliding with the walls equally often in all directions. Because the pressure of an enclosed fluid is transmitted equally throughout it, the force per unit area on the walls is the same everywhere, so the pressure has the same value at every point.
Example 2 (2 marks)
Treating the asteroid 2023 DZ2 as a simple sphere 64 m in diameter, calculate its volume, using: volume of a sphere = (4/3)πr³, where r is the sphere's radius.
Show the worked answer
Radius r = 64/2 = 32 m. V = (4/3) pi r³ = (4/3) x pi x 32³ = (4/3) x pi x 32768 = 1.37 x 10⁵ m³.
Example 3 (2 marks)
A gas bubble travels upwards from the school of fish (at a depth of 360 m) to the sea surface. Atmospheric pressure is 100 kPa and seawater has a density of 1030 kg m^-3. (c)(ii) If the bubble has a volume of 2.0 mm^3 at the 360 m depth, work out its volume just as it is about to break the sea surface. size of bubble = ......
Show the worked answer
Pressure at 360 m depth: p1 = atmospheric + rho g h = 100,000 + 1030 x 10 x 360 = 3,808,000 Pa. Pressure at surface: p2 = 100,000 Pa. Temperature constant, so Boyle's law: p1 V1 = p2 V2. V2 = p1 V1 / p2 = 3,808,000 x 2.0 / 100,000 = 76 mm³.
More worked questions on this topic
- A solid rubber bicycle tyre rests on the ground. The bicycle plus rider has a mass of 60 kg, th (3 marks)
More O-Level Pure Physics topics
Physical Quantities, Units and Measurement · Kinematics · Dynamics · Turning Effects of Forces · Energy · Kinetic Particle Model of Matter · all of O-Level Pure Physics