AQA
GCSE
Physics
P1 (Unit 1)
Summary
Notes
, P1.1/2/3/4 Energy transfer, using and generating electricity
Heat radiation
Infrared waves are part of the electromagnetic spectrum. They are part of the
spectrum just beyond visible red light. We can detect infrared radiation with
our skin- it makes us feel warm
All objects emit( give off) infrared radiation
If an object is hotter than its surroundings, it emits more radiation than it
absorbs , if an object is cooler than its surrounding then it absorbs more
radiation than it emits
The hotter an object is, the more infrared radiation it emits in a given times.
Infrared radiation can travel through a vacuum, as in travelling through space;
this is how we get energy from the sun.
There are 3 types of heat transfer : conduction, convection and radiation
Conduction and convection involve the transfer of energy through particles
Conduction is the main form of heat transfer in solids
Convection is the main form of heat transfer in liquids and gasses.
Surfaces and radiation
Dark, matt surfaces are good absorbers of infrared radiation. An object that
is dull and black, left in the sun would become much hotter than the same
objected painted shiny white.
Dark, matt surfaces are also good emitters of infrared radiation, so an object
that is painted dull and black will transfer energy and cool down more quickly
than an object painted shiny white.
Light, shiny surfaces are good reflectors of infrared radiation
States of matter and kinetic theory
There are 3 states of matter : solids, liquids and gasses
In solids, strong forces of attraction hold the particles close together in a fixed
regular arrangement. The particles don’t have much energy so they can only
vibrate about their fixed positions.
In liquids, there are weaker forces of attraction between the particles, the
particles are close together, but can move past each other and form irregular
arrangements. They have more energy than particles in a solid and they move
in random directions at low speeds.
In gasses, there are almost no forces of attraction between the particles.
They have more energy than in solids and liquids and are free to move and
travel in random directions at high speeds.
When you heat a substance, you give its particles more kinetic energy, they
vibrate and move faster. This is what eventually causes solids to melt and
liquids to boil.
, Conduction
Conduction of heat energy is the process where vibrating particles pass
on their extra kinetic energy to neighbouring particles.
This mainly occurs in solids
Usually conduction is faster in denser solids, because the particles are
closer together and so will collide more often and pass energy between them,
materials that have large spaces between them conduct energy more slowly,
these materials are called insulators.
Metals conduct electricity well because they have electrons that are free to
move around. The electrons at the hot part of the metal will move faster and
collide with other free electrons and transfer energy. These other electrons will
transfer their extra energy to other electrons and so on. Because the electrons
move freely, this is obviously a much fast way of transferring energy
.
Convection
Convection occurs when the more energetic particles more from a
hotter region to a cooler region, taking their heat energy with them.
When a fluid is heated it expands. The fluid becomes less dense and rises.
Warm fluid is replaced by cooler, denser fluid. The resulting convection
currents transfer energy thorough the fluid.
Convection currents are therefore all about changes in density
Convection currents come in all scales, from a simple heater in a room to
convection currents moving tectonic plates causing earthquakes.
Evaporation and condensation
Evaporation occurs when a liquid turns into a gas. Evaporation takes place
because the most energetic liquid molecules escape from the liquids surface
and also breaks from the forces of attraction to enter the air. Therefore the
average kinetic energy of the remaining molecules is less so the temperature
of the liquid decreases. This means that evaporation causes cooling.
Condensation occurs when a gas turns into a liquid. The gas cools and
slows down losing kinetic energy. The attractive forces also start to pull the
gas together. If the temperature can get cold enough then the gas can turn
into a liquid and condense.
The rate of evaporation will be faster if :
o The temperature is higher: at higher temperatures, the average
particle energy will be higher so they will have more energy to escape
o Density is lower, the forces of attraction between the particles are
weaker so more particles will have enough energy to overcome these
forces and escape the liquid.
o Surface area is larger, more particles will be near enough to the
surface to escape the liquid
GCSE
Physics
P1 (Unit 1)
Summary
Notes
, P1.1/2/3/4 Energy transfer, using and generating electricity
Heat radiation
Infrared waves are part of the electromagnetic spectrum. They are part of the
spectrum just beyond visible red light. We can detect infrared radiation with
our skin- it makes us feel warm
All objects emit( give off) infrared radiation
If an object is hotter than its surroundings, it emits more radiation than it
absorbs , if an object is cooler than its surrounding then it absorbs more
radiation than it emits
The hotter an object is, the more infrared radiation it emits in a given times.
Infrared radiation can travel through a vacuum, as in travelling through space;
this is how we get energy from the sun.
There are 3 types of heat transfer : conduction, convection and radiation
Conduction and convection involve the transfer of energy through particles
Conduction is the main form of heat transfer in solids
Convection is the main form of heat transfer in liquids and gasses.
Surfaces and radiation
Dark, matt surfaces are good absorbers of infrared radiation. An object that
is dull and black, left in the sun would become much hotter than the same
objected painted shiny white.
Dark, matt surfaces are also good emitters of infrared radiation, so an object
that is painted dull and black will transfer energy and cool down more quickly
than an object painted shiny white.
Light, shiny surfaces are good reflectors of infrared radiation
States of matter and kinetic theory
There are 3 states of matter : solids, liquids and gasses
In solids, strong forces of attraction hold the particles close together in a fixed
regular arrangement. The particles don’t have much energy so they can only
vibrate about their fixed positions.
In liquids, there are weaker forces of attraction between the particles, the
particles are close together, but can move past each other and form irregular
arrangements. They have more energy than particles in a solid and they move
in random directions at low speeds.
In gasses, there are almost no forces of attraction between the particles.
They have more energy than in solids and liquids and are free to move and
travel in random directions at high speeds.
When you heat a substance, you give its particles more kinetic energy, they
vibrate and move faster. This is what eventually causes solids to melt and
liquids to boil.
, Conduction
Conduction of heat energy is the process where vibrating particles pass
on their extra kinetic energy to neighbouring particles.
This mainly occurs in solids
Usually conduction is faster in denser solids, because the particles are
closer together and so will collide more often and pass energy between them,
materials that have large spaces between them conduct energy more slowly,
these materials are called insulators.
Metals conduct electricity well because they have electrons that are free to
move around. The electrons at the hot part of the metal will move faster and
collide with other free electrons and transfer energy. These other electrons will
transfer their extra energy to other electrons and so on. Because the electrons
move freely, this is obviously a much fast way of transferring energy
.
Convection
Convection occurs when the more energetic particles more from a
hotter region to a cooler region, taking their heat energy with them.
When a fluid is heated it expands. The fluid becomes less dense and rises.
Warm fluid is replaced by cooler, denser fluid. The resulting convection
currents transfer energy thorough the fluid.
Convection currents are therefore all about changes in density
Convection currents come in all scales, from a simple heater in a room to
convection currents moving tectonic plates causing earthquakes.
Evaporation and condensation
Evaporation occurs when a liquid turns into a gas. Evaporation takes place
because the most energetic liquid molecules escape from the liquids surface
and also breaks from the forces of attraction to enter the air. Therefore the
average kinetic energy of the remaining molecules is less so the temperature
of the liquid decreases. This means that evaporation causes cooling.
Condensation occurs when a gas turns into a liquid. The gas cools and
slows down losing kinetic energy. The attractive forces also start to pull the
gas together. If the temperature can get cold enough then the gas can turn
into a liquid and condense.
The rate of evaporation will be faster if :
o The temperature is higher: at higher temperatures, the average
particle energy will be higher so they will have more energy to escape
o Density is lower, the forces of attraction between the particles are
weaker so more particles will have enough energy to overcome these
forces and escape the liquid.
o Surface area is larger, more particles will be near enough to the
surface to escape the liquid
