Flashcards in P1 1 Transfer Of Energy Deck (26)
What is infrared radiation?
Infrared radiation is energy transfer by electromagnetic waves.
Can all objects emit infrared radiation?
Yes all objects can emit infrared radiation.
Also, the hotter an object is, the more infrared radiation it emits in a given time.
Which surfaces are the best emitters of radiation?
• Dark, mart surfaces emit more infrared radiation than light, shiny surfaces
Which surfaces are the best absorbers and reflectors of radiation?
• Dark, matt surfaces absorb more infrared radiation than light shiny surfaces
• Light, shiny surfaces reflect more infrared radiation than dark matt surfaces
Name some properties which are used to describe states of matter:
Describe the properties of a solid:
• Can't flow
• Fixed shape
• Fixed volume
• Much higher density than a gas
Describe the properties of a liquid:
• Can flow
• Fits a container shape
• Has a fixed volume
• Much higher density than a gas
Describe the properties of a gas:
• Can flow
• Fills container
• Its volume can be changed
• Has a low density compared with a solid or liquid
The kinetic theory of matter:
• The particles in a solid are held to each other in fixed positions
• They vibrate about their fixed positions
• The particles in a liquid are in contact with each other
• They move about at random
• The particles in a gas move about randomly and are much further apart than particles in a solid or liquid
- The particles in a gas have more energy than those in a liquid, which have more energy than those in a solid.
Conduction in metals:
• Metals contain lots of free electrons. These electrons move about at random inside the metal and hold the positive metal ions together
• When a metal rod is heated at one end, the free electrons at the hot end gain kinetic energy and diffuse across the metal
• As a result, they transfer energy to the surrounding electrons and ions
What is convection?
Convection is the circulation of a fluid (liquid or gas).
How does convection work?
The circulation currents are caused because fluids rise when they are heated. So they become less dense. Then, they fall as they could down as cooling makes them more dense. Convection currents transfer energy from the hotter parts to the cooler parts.
Uses of convection:
• Hot water at home
• Sea breezes
• Lava lamps
What is evaporation?
Evaporation is when a liquid turns into a gas.
What is condensation?
Condensation is when a gas turns into a liquid.
How does the 'cooling effect' work in evaporation?
• Weak attractive forces exist between the molecules in the liquid
• The faster molecules which have more kinetic energy break away from the attraction of the other molecules and leave the liquid
• After they leave, the liquid is cooler as the average kinetic energy of the remaining molecules in the liquid has decreased
How to increase the rate of evaporation:
• Increase the surface area of the liquid
• Increase the temperature of the liquid
• Create a draught of air across the liquid's surface
The process of condensation:
• The air in a room is moist or 'humid'
• A glass pane is a cold surface so water vapour will hit the mirror and cool down
How to increase the rate of condensation:
• Increase the surface area
• Reduce the temperature of the surface
What does the rate of energy transferred to or from an object depend on?
• The shape, size, and type of material of the object
• The materials the object is in contact with
• The temperature difference between the difference between the object and its surroundings
What does the temperature rise of an object depend on?
• The amount of energy supplied to it
• The mass of the substance
• What the substance is
What is the specific heat capacity of an object?
The specific heat capacity of a substance is the energy needed or energy transferred to 1 kg of the substance to raise its temperature by 1 degree C.
Change of temperature equation:
E = m x c x θ
E = energy transferred in J
c = specific heat capacity J/kg/degrees C
m = mass in kg
θ = temperature change in degrees C
Energy transfer from our homes can be reduced by fitting:
• Loft insulation
• Cavity wall insulation
• Double glazing
• Draught proofing
• Aluminium foil behind radiators
What do U-values tell us?
U-values tell us how much energy per second passes through different materials.
The lower the U-value, the more effective the material is as an insulator.