Physics chapter 11 Flashcards
name 3 ways thermal energy is transfered?
Conduction, Convection, and radiation
Define conduction?
The process by which thermal energy is transmitted through a medium from one particle to another
When does Thermal energy transfer stop?
When both particles are the same tampature.
Why is the conduction of thermal energy better in metals compared to other solids?
It is because the thermal energy is transmitted through both the vibrating molecules and the free electrons.
Why is a vacuum a perfect insulator?
It is a perfect insulator because conduction cannot occur when there are no particles present
Why are gas a liquids poor heat conductors?
Because the particles are far apart.
What is a material that does not conduct heat called?
An insulator
Define convection?
It is the process by which thermal energy is transmitted from one place to another by the movement by the movement of heated particles of a gas or liquid.
What happens to the density of air when it is heated?
It decreases
Define convection current?
When hot liquid/gas floats due to lower density its place is taken by the falling cold and denser gas/liquid. The cold gas/liquid is then heated and floats up.
Define radiation?
The transfer of thermal energy by electromagnetic waves.
Why can radiation take place in a vacuum?
Because it does not need a medium to transfer thermal energy.
What is the source of thermal energy is radiation?
Infra-red raditation
How do the light from the sun and other stars reach us?
It gets to us in the form of electromagnetic radiation.
How does infra-red radiation travel?
It travels in a straight line
Dull-black surface qualities?
They are very good absorbers and emitters of heat
Silver/white surface qualities?
They are poor absorbers and emitters` of heat.
Factors that affect the rate of radiation?
- The type of surface - Black surface cools faster through radiation
- The temperature of the surface - A hotter surface radiates energy at a greater rate
- The surface area - Energy is radiated at a greater rate from a bigger surface area
What is the rate of energy escaping from us?
100 J/s
Methods of insulating a house?
- Thick curtains (To prevent heat from escaping and cold from entering?
- Loft and underfloor insulating material (Prevents conduction of heat through floors and ceiling)
- Double and triple glazing of windows (Vacuum between the panels helps prevent heat loss from conduction and convection)
- Cavity walls ( Reduces heat loss through conduction)
- Foam in wall cavity (Reduces heat loss through convection)
