CIE iGCSE Co-ordinated Sciences-P2.3.2 Convection- Study Notes- New Syllabus
CIE iGCSE Co-ordinated Sciences-P2.3.2 Convection – Study Notes
CIE iGCSE Co-ordinated Sciences-P2.3.2 Convection – Study Notes -CIE iGCSE Co-ordinated Sciences – per latest Syllabus.
Key Concepts:
Core
- Know that convection is an important method of energy transfer in liquids and gases
Supplement
- Describe convection in liquids and gases
- Explain convection in liquid and gases in terms of density changes
CIE iGCSE Co-Ordinated Sciences-Concise Summary Notes- All Topics
Convection
Convection is the transfer of heat energy in liquids and gases by the movement of particles in currents. It is an important method of energy transfer in fluids.
Explanation Using the Particle Model:
- When a fluid (liquid or gas) is heated, the particles gain kinetic energy and move faster.
- The heated fluid expands, becomes less dense, and rises.
- Cooler, denser fluid sinks to take its place.
- This sets up a convection current that transfers heat through the fluid.
Key Features of Convection:
- Only occurs in liquids and gases (not solids, since particles in solids cannot move freely).
- Involves the bulk movement of particles, unlike conduction.
- Relies on density differences caused by heating and cooling.
Examples of Convection:
- Water heating in a pan → hot water rises, cooler water sinks.
- Sea breezes → warm air over land rises, cooler air from the sea moves in.
- Hot air balloons → air inside balloon is heated, becomes less dense, and rises.
Example :
Explain why smoke from a fire rises upwards in terms of convection.
▶️ Answer/Explanation
Step 1: The air near the fire is heated → particles move faster and spread apart.
Step 2: This air becomes less dense and rises, carrying smoke with it.
Step 3: Cooler surrounding air moves in to replace it, forming a convection current.
Final Answer: Smoke rises because hot air expands, becomes less dense, and rises, setting up convection currents.
Convection in Liquids and Gases
Convection is the transfer of heat in liquids and gases by the bulk movement of particles due to density differences.
Explanation in Liquids:
- When part of a liquid is heated, the particles gain kinetic energy and move faster.
- The liquid expands, so the same mass of liquid now occupies a larger volume → its density decreases.
- The warmer, less dense liquid rises, while cooler, denser liquid sinks to take its place.
- This sets up a convection current, transferring heat throughout the liquid.
Explanation in Gases:
- When part of a gas is heated, its particles move faster and spread apart.
- The gas expands → its density decreases.
- The warmer, less dense gas rises, while cooler, denser gas sinks downwards.
- This creates convection currents in the gas.
Key Idea: Density Changes Drive Convection
- Heating → particles spread out → density decreases → fluid rises.
- Cooling → particles come closer → density increases → fluid sinks.
- This cycle continues to form convection currents.
Examples:
- Liquids: Water heating in a pan – hot water at the bottom rises, cooler water sinks, forming a convection current.
- Gases: Sea breezes – warm air over land rises during the day, cooler air from the sea moves in.
Summary Table
| Step | Effect |
|---|---|
| Heating | Particles move faster, spread apart, density decreases |
| Rising | Less dense region rises upwards |
| Cooling | Particles slow down, come closer, density increases |
| Sinking | Cooler, denser fluid sinks down |
Example :
Explain why hot air rises above a radiator in a room using the idea of density.
▶️ Answer/Explanation
Step 1: Air near the radiator is heated → particles gain energy and spread apart.
Step 2: The heated air expands, becomes less dense, and rises.
Step 3: Cooler, denser air moves in to take its place near the radiator.
Final Answer: A convection current is formed, circulating warm air around the room.