IB MYP 4-5 Physics- Heat transfers: Conduction, Convection and Radiation- Study Notes - New Syllabus
IB MYP 4-5 Physics-Heat transfers: Conduction, Convection and Radiation- Study Notes
Key Concepts
- Heat transfers: Conduction, Convection and Radiation
Heat transfers: Conduction, Convection and Radiation
Heat Transfers
Heat transfer is the process by which thermal energy moves from one object or region to another due to a difference in temperature.
There are three main methods of heat transfer:
- Conduction – Heat transfer through direct contact of particles.
- Convection – Heat transfer through movement of fluids (liquids or gases).
- Radiation – Heat transfer through electromagnetic waves without needing matter.
Conduction
Conduction is the transfer of heat through a material without the movement of the material itself. It occurs due to the vibration and collision of particles in solids, especially metals.
In metals, free electrons transfer energy rapidly, making them good conductors. In non-metals, conduction happens mainly via vibration of atoms (lattice vibrations), making them poorer conductors.
- Good conductors: Copper, aluminum, silver.
- Poor conductors (insulators): Wood, plastic, rubber, air.
Factors affecting conduction rate:
- Material type (thermal conductivity)
- Temperature difference between ends
- Cross-sectional area of the material
- Length of the material
Example:
Why does a metal spoon in a hot soup become hot quickly compared to a wooden spoon?
▶️ Answer/Explanation
Metals have free electrons that move and transfer energy efficiently. The heat from the soup is transferred along the metal spoon faster than along the wooden spoon, making the metal spoon hot more quickly.
Example:
Why are cooking pots made of metal but have plastic handles?
▶️ Answer/Explanation
The pot body is made of metal to conduct heat quickly to cook food, while the handles are plastic to prevent heat conduction to the user’s hands, reducing burn risk.
Convection
Convection is the transfer of heat through the movement of a fluid (liquid or gas) caused by differences in density due to temperature changes.
When a fluid is heated, it expands, becomes less dense, and rises. Cooler, denser fluid moves in to replace it, creating a convection current. This process repeats, distributing heat throughout the fluid.
- Natural convection – Occurs due to density differences without external forces.
- Forced convection – Movement is aided by fans or pumps.
Factors affecting convection rate:
- Temperature difference between fluid regions
- Viscosity of the fluid
- Shape and size of the container
Example:
Why does warm air rise in a room when a heater is turned on?
▶️ Answer/Explanation
The heater warms nearby air, making it less dense, so it rises. Cooler, denser air moves down to replace it, setting up a convection current in the room.
Example:
How does a sea breeze form?
▶️ Answer/Explanation
During the day, land heats up faster than sea water. Warm air over land rises, and cooler air from the sea moves in to replace it, creating a sea breeze.
Radiation
Radiation is the transfer of heat via electromagnetic waves (mainly infrared) without requiring a medium. It can occur through empty space (vacuum).
All objects emit thermal radiation; hotter objects emit more and at shorter wavelengths. The rate of heat transfer by radiation depends on the surface properties of the object.
- Good emitters & absorbers: Dull, dark surfaces.
- Poor emitters & absorbers: Shiny, light-colored surfaces.
Factors affecting radiation rate:
- Temperature of the object
- Surface color and texture
- Surface area
Example:
Why are solar panels often black?
▶️ Answer/Explanation
Black surfaces absorb more radiation from sunlight, increasing efficiency in converting light energy to electrical energy.
Example:
Why are the inside surfaces of thermos flasks shiny?
▶️ Answer/Explanation
Shiny surfaces reflect infrared radiation, reducing heat loss and keeping the liquid hot or cold for longer.