Physics GCSE

Revision cards of GCSE unit 1 physics for core science.

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Heat is transferred in three different ways

  • Heat energy can by transferred by radiation, conduction or convection.
  • Heat radiation is the transfer of heat energy by infrared radiation.
  • Conduction and convection involve the transfer of energy by particles.
  • Conduction is the main form of heat transfer in solids.
  • Convection is the main form of heat transfer in liquids and gases.
  • Infrared radiation can be emitted by solids, liquids and gases.
  • Any object can both absorb and emit infrared radiation, wheher or not conduction or convection are also takig place.
  • The bigger the temperature differene between a body and its surroundings, the faster energy is transferred by heating.
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Infrared radiation-Emission of electromagnetic wav

  • All objects are continually emitting and absorbing infrared radiation. Infrared radiation is emitted from the surface of an object.
  • An object that's hotter than its surrounding emits more radiaion than it absorbs (as it cools down). And an object that's cooler than its surroundings absorbs more radation than it emits (a it warms up).
  • The hotter an object is, the more radiatio it radiats in a given time.
  • You can feel this infrared radiation if you sand near something hot.
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Surfaces

  • Dark, matt surfaces absorb infrared radiation better than light shiny surfaces. They also emit much more infrared radiation.
  • Light shiny surfaces reflect a lot of the infrared radiation.
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Conduction

  • Conduction of heat occurs mainly in solids.
  • Conduction of heat is the process where vibrating particles pass on their extra kinetic energy to neighbouring particles.
  • Metals are good conductors because of theire free electrons.
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Convection

Convection occurs when the more energetic particles more from the hotter region to the cooler region and take their heat energy with them.

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Condensation

  • Condensation is when a gas turns to a liquid
  • When a gas cools, the particles in the gas slow down and lose kinetic energy. The attractive forces between the particles pull them closer together.
  • If the temperature gets cold enough and the gas particles get close enough together that condensation can take place, the gas becomes a liquid.
  • Wate vapour in the air condenses when it comes into contact with cold surfacese.g drink glasses.
  • The steam you see risin fro a boiling kettle is actually invisible water vapour condensing to form tiny water drplets as it spreads into cooler air.
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The rate of condensation can vary

The rate of condensation will be faster if the:

  • Temperature of the gas is lower- the average particle anergy in the gas is lower- so more oarticles will slow down enough to clump together and form liquid droplets.
  • Temperature of the surface the gas touches is lower.
  • Density is higher- the forces between the particles will be stronger. Fewer particles will have enough energy to overcome these forces and will instead clump together and form a liquid.
  • Airflow is less- the concentration of the substance in the ai will be higher, and so the rate of condensation will be greater.
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Evaporation

Evaporation is when liquid turns into a gas

  • Evaporation is when partices escape from a liquid 
  • Particles can evaporate from a liquid at temperatures that are much lower than the liquid boiling point
  • Particles near the surface of a liquid can escape and become gas articles if:

The particles are travelling in the right direction to escape the liquid. The particles are travelling fast enough to overcome the attractive forces of the other particles in the liquid.

  • The fastest particles are most likely to evaporate from the liquid- so when they do, the average speed and kinetic energy of the remaining particles decreases.
  • This decrease in average particle energy means the temperature of the remaining liquid falls.
  • This cooling effect can be really useful. For example, you sweat when you excercise or get hot. As the water from the sweat on your skin evaporates, it cools you down.
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The rate of evaporation can vary

The rate of evaporation will be faster if the:

  • tempeature is higher- the average particle energy will be higher, so more particles will have enough energy to escape.
  • Density is lower- the forces between the particles will usualy be weaker, so more particles will have enough energy to overcome these forces and escape the liquid.
  • Surface area is larger- more particles will be near enough to the surface to escape the liquid.
  • Airflow over the liquid is greater- the lower the concentration of an evaporating substance in the air it's evaporating into, the higher the rate of evaportaion. A greater airflow means air above the liquid is replaced more quickly, so the concentration in the air will be lower.
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Specific heat capacity

  • It takes more heat energy to increase the temperature of somematerials than others. E.g you need 4200j to warm 1kg of water by 1C but only 139j to warm 1kg of mercury by 1C.
  • Materials which need to gain lots of energy to warm up, also release loads of energy when they cool again. The can 'store' a lot of heat.
  • The measure of how much energy a substance can store is called its specific heat capacity.
  • Specific heat capacity is the amount of energy needed to raise the temperature of 1kg of a substance by 1C. Water has a specific heat capacity of 4200J/KG.

Formula for specific heat capacity:

E= M x C x Temp change

E= energy transferred M= mass C= specific heat capacity

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Different typs of energy

  • Electrical energy
  • Kinetic energy
  • Thermal energy
  • Light energy
  • Sound energy
  • Nuclear energy
  • Gravitational potential energy
  • Elastic potential energy
  • Chemical energy
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Conservation of energy principle

Energy can be transferred usefully from one form to another. But it can never be created or destroyed.

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Different typs of energy

  • Electrical energy
  • Kinetic energy
  • Thermal energy
  • Light energy
  • Sound energy
  • Nuclear energy
  • Gravitational potential energy
  • Elastic potential energy
  • Chemical energy
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Conservation of energy principle

Energy can be transferred usefully from one form to another. But it can never be created or destroyed.

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Comments

Former Member

niiice one, cheers :-)

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