2.1.2Thermal Physics
Particle Model — Cambridge IGCSE Physics 0625 Revision Notes & Topical Questions
5 min read 9 parts Lesson 6 of 45 1 quiz
Lesson summary
2.1.2 Particle Model — IGCSE PHYSICS notes: Describe the particle model of solids, liquids and gases, temperature, gas pressure and Brownian motion.Solid — particles are closely packed in a regular arrangement, vibrate about fixed positions and have strong forces between them.Liq…
- Properties follow from forces and distances (Extended)
- Absolute zero
- Concentration gradient
- Random motion
- Liquid — particles are close together in an irregular arrangement, move around each other and have weaker forces
- Increasing the temperature increases the average kinetic energy of the particles
Section 1 of 9Particle structure of the three states
Particle structure of the three states
Solid
- Solid particles are closely packed in a regular arrangement, vibrate about fixed positions and have strong forces between them.
Liquid
- Liquid particles are close together in an irregular arrangement, move around each other and have weaker forces.
Gas
- Gas particles are far apart in a random arrangement, move quickly in random directions and have very weak forces except during collisions.
Properties follow from forces and distances (Extended)
- Properties follow from forces and distances (Extended) gases are compressible because of the large spaces between particles.
Section 2 of 9Temperature and absolute zero
Increasing the temperature increases the average kinetic energy of the particles.
Absolute zero
−273 °C, the lowest possible temperature, where particles have the least kinetic energy.
Section 3 of 9Gas pressure
Gas pressure
Gas pressure is caused by particles colliding with the walls of the container and exerting a force on them.
Faster particles collide with the walls more often and with greater force, so the pressure is greater.
Extended explanation:
- Each collision changes the momentum of a particle.
- The wall exerts a force on the particle to cause this, and the particle exerts an equal and opposite force on the wall.
- Pressure = total force per unit area of wall.
Section 4 of 9Brownian motion
Brownian motion
Brownian motion the random, jerky motion of small visible particles, such as smoke in air or pollen in water.
It is caused by being hit by the invisible, fast-moving molecules of the fluid.
It is evidence for the kinetic particle model.
Extended
- Extended the tiny particles are struck unevenly by many light, fast molecules, so the resultant force on them changes randomly.
Section 5 of 9Observing Brownian motion
1
Fill a small glass smoke cell with smoke from a burning straw and cover it.
2
Place the cell under a microscope and shine light in from the side.
3
Focus on the bright specks of smoke.
4
Observe their random, jerky movement.
5
Explain the motion as caused by collisions with unseen air molecules.
Section 6 of 9Diffusion
Diffusion
Diffusion the spreading of particles from a region of high concentration to a region of low concentration.
It happens because particles move randomly, and it stops when the concentration is even.
It is evidence that particles are always moving.
It is fastest in gases, slower in liquids and extremely slow in solids, where particles only vibrate.
A higher temperature makes diffusion faster because the particles move faster.
Section 7 of 9More from the specification
More from the specification
Particle model
- Particle model matter is made of tiny particles whose arrangement and motion explain the properties of solids, liquids and gases
Definite volume and shape
- Definite volume and shape solids keep both, liquids keep a definite volume but take the shape of the container, gases have neither
Kelvin scale
- Kelvin scale absolute temperature in kelvin equals degrees Celsius plus 273, and zero kelvin is the lowest possible temperature
Gas pressure
- Gas pressure particles colliding with container walls cause pressure,
- so a balloon expands when heated at constant pressure because particles move faster
Particle model
- Particle model matter is made of tiny particles whose arrangement and motion explain the properties of solids, liquids and gases
Definite volume and shape
- Definite volume and shape solids keep both, liquids keep a definite volume but take the shape of the container, gases have neither
Kelvin scale
- Kelvin scale absolute temperature in kelvin equals degrees Celsius plus 273, and zero kelvin is the lowest possible temperature
Gas pressure
- Gas pressure particles colliding with container walls cause pressure,
- so a balloon expands when heated at constant pressure because particles move faster
Average speed
- Total distance divided by total time.
Volume
- The amount of space an object occupies.
Constant
- Not changing.
Kelvin
- SI unit of temperature on the absolute scale.
Constant volume
- The container is rigid and sealed.
Inversely proportional
- One quantity falls as the other rises in the same ratio.
p1V1
p1V1 p2V2
What the symbols mean: p1, V1 = pressure and volume before · p2, V2 = after; only for a fixed mass of gas at constant temperature
Section 8 of 9Key terms
| Term | Meaning |
|---|---|
| Diffusion | Spreading of particles from high to low concentration. |
| Brownian motion | Random jiggling of small visible particles hit by fluid molecules. |
| Concentration gradient | Difference in concentration between two areas. |
| Absolute zero | Lowest possible temperature, −273 °C. |
| Gas pressure | Force per unit area caused by particle collisions with the walls. |
| Random motion | Movement in no specific path with sudden changes at collisions. |
Section 9 of 9Exam technique
1
Saying diffusion happens in solids at a noticeable rate — it is extremely slow.
2
Saying the particles of smoke are the air molecules — the visible specks are much larger than molecules.
3
Saying gas pressure comes from particles hitting each other — it comes from collisions with the walls.
4
Saying the particles themselves get hot or expand.
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