Energy transfers by heating Flashcards
thermal conductivity
the thermal conductivity of a material tells you how quickly energy is transmitted through my thermal conduction
how can you test thermal conductivity?
you can test the thermal conductivity of rods made of different metals:
each rod must have the same diameter + length + same temperature difference between its ends
one on each rod is covered in wax and the other ends are heated equally.
The faster the wax melts, the higher the thermal conductivity of the metal
heating bills can be expensive…
heating bills can be expensive so it is important to reduce the rate of heat loss from buildings.
what are the factors affecting the rate of heat loss from a building?
- the thickness of its walls and roof
- the thermal conductivity of its walls and roof
lower thermal conductivity = …
lower thermal conductivity = lower rate of heat losswhat can the thermal conductivity of the walls and roof be reduced by?
what can the thermal conductivity of the walls and roof be reduced by?
the thermal conductivity of the walls and roof be reduced by thermal insulators
what’s a thermal insulator?
a thermal insulator is a material which has a low thermal conductivity.
whats the rate of energy transfer through an insulator?
the rate of energy transfer through an insulator is low.
what does the energy transfers per second depend on?
- the material’s thermal conductivity
- the temperature difference between the 2 sides of the material.
- the thickness of the material
When a substance is heated or cooled the temperature change depends on….
the substance’s mass
the type of material
how much energy is transferred to it
What type of capacity does every type of material have?
specific heat capacity
specific heat capacity
the amount of energy needed to raise the temperature of 1kg of a substance by 1°C.
how can energy being transferred to the thermal store of a substance be calculated?
the energy transferred to the thermal store of a substance can be calculated from the substance’s:
mass
SHC
temperature change
state the equation for the change in thermal energy.
∆E = m c ∆θ
∆E = change in thermal energy (J)
m = mass (kg)
c = SHC (J/kg°C)
∆θ = temperature change (°C)
infrared radiation is…
infrared radiation is a part of the electromagnetic spectrum
what do all objects do in terms of infrared radiation?
all objects emit and absorb infrared radiation.
what does it mean for the infrared radiation if there’s a high temperature of an object?
the higher the temperature of an object, the more infrared radiation it emits in a given time.
a good absorber of infrared radiation is = ?
a good absorber of infrared radiation is also a good emitter
for an object at a constant temperature:
infrared radiation emitted = infrared radiation absorbed
infrared radiation is emitted across a continuous range of wavelengths
what would happen to an objects temperature if it absorbs infrared radiation at a higher rate than it emits it?
an objects temperature will increase if it absorbs infrared radiation at a higher rate than it emits it. this rule applies to the planet earth
whats a “black body”?
a black body is a theoretical object that absorbs 100% of the radiation that falls on it.
what would a perfect black body do?
a perfect black body would not reflect or transmit any radiation. and would also be a perfect emitter of radiation.
what are some factors that the temperature of the earth depends on?
the temperature of the earth depends on lots of factors including:
the rate of which visible light are:
reflected
absorbed
and emitted
by the Earth’s atmosphere and surface.
describe how greenhouse gases take part in increasing the temperature on earth.
- GH gases absorb infrared radiation emitted by the surface of the earth —- prevent it escaping into space
- they then re-emit the infrared radiation back towards the surface of the earth —– increasing the earths temperature.
