Physics notes – Energy resources and transfers
Energy
Energy stores
Energy can be stored in many different ways:
Kinetic energy Determined by speed and mass
Electrostatic energy Between objects that are charged
Gravitational energy Determined by height in relation to a base line and mass
Elastic/Strain energy Objects that are squashed or stretched e.g. a catapult
Thermal energy When an object is hot/heated it possesses thermal energy
Chemical energy Chemicals that can react or burn, such as food or fuel
Nuclear energy Objects that undergo fusion or radioactive decay e.g. the sun
Magnetic energy The energy in a magnetic field
Energy transfers
Mechanically e.g. when gravity accelerates an object and gives it kinetic energy.
Electrically e.g. when a current passes through a lamp and it emits light and heat.
, By heating e.g. when a fire is used to heat up an object.
By radiation e.g. when vibrations cause waves to travel through the air as sound, or an object emits
electromagnetic radiation.
The Law of conservation of energy
Energy can never be created or destroyed. It can only be transferred from one form to another.
Efficiency in heat transfer
What is Efficiency
Efficiency is a measure of how much energy is transferred usefully to an object compared to how much
total energy is used up.
E.g. In a light bulb that burns for 10 mins, 6 x 10 4 J of energy are given to the bulb, but only 4800J of light energy is
emitted, the rest of the energy is lost as heat energy.
The efficiency of this light bulb in percent is:
4800/6 x 104 X 100
= 8% efficiency
Sankey diagrams
These diagrams show energy efficiency:
E.g, a light bulb takes 100J of energy and gives out 10J of
light energy. 90J are wasted.
Heat transfer Mechanisms
Definitions
Temperature
the average kinetic energy per molecule
Thermal energy
The total internal kinetic energy of an objejct
Conduction:
What does it occur in
Solids
How does it work
In solids the particles vibrate and this kinetic Energy is transferred by collisions between them
Conductors and insulators:
Materials that are good at conducting thermal energy are called conductors, and if they are not they are
called insulators.
Solid metals are good conductors because the particles are close together so it is easier to transfer
energy.
They also have delocalised electrons that collide with ions throughout the metal and transfer heat
energy.
Conduction experiments:
Ice melts far quicker on metal because it is a good conductor.
The metal at room temperature conducts its heat towards the ice at less than 0oC, so it melts quickly
The wood does not conduct it heat and insulated it instead.
Energy
Energy stores
Energy can be stored in many different ways:
Kinetic energy Determined by speed and mass
Electrostatic energy Between objects that are charged
Gravitational energy Determined by height in relation to a base line and mass
Elastic/Strain energy Objects that are squashed or stretched e.g. a catapult
Thermal energy When an object is hot/heated it possesses thermal energy
Chemical energy Chemicals that can react or burn, such as food or fuel
Nuclear energy Objects that undergo fusion or radioactive decay e.g. the sun
Magnetic energy The energy in a magnetic field
Energy transfers
Mechanically e.g. when gravity accelerates an object and gives it kinetic energy.
Electrically e.g. when a current passes through a lamp and it emits light and heat.
, By heating e.g. when a fire is used to heat up an object.
By radiation e.g. when vibrations cause waves to travel through the air as sound, or an object emits
electromagnetic radiation.
The Law of conservation of energy
Energy can never be created or destroyed. It can only be transferred from one form to another.
Efficiency in heat transfer
What is Efficiency
Efficiency is a measure of how much energy is transferred usefully to an object compared to how much
total energy is used up.
E.g. In a light bulb that burns for 10 mins, 6 x 10 4 J of energy are given to the bulb, but only 4800J of light energy is
emitted, the rest of the energy is lost as heat energy.
The efficiency of this light bulb in percent is:
4800/6 x 104 X 100
= 8% efficiency
Sankey diagrams
These diagrams show energy efficiency:
E.g, a light bulb takes 100J of energy and gives out 10J of
light energy. 90J are wasted.
Heat transfer Mechanisms
Definitions
Temperature
the average kinetic energy per molecule
Thermal energy
The total internal kinetic energy of an objejct
Conduction:
What does it occur in
Solids
How does it work
In solids the particles vibrate and this kinetic Energy is transferred by collisions between them
Conductors and insulators:
Materials that are good at conducting thermal energy are called conductors, and if they are not they are
called insulators.
Solid metals are good conductors because the particles are close together so it is easier to transfer
energy.
They also have delocalised electrons that collide with ions throughout the metal and transfer heat
energy.
Conduction experiments:
Ice melts far quicker on metal because it is a good conductor.
The metal at room temperature conducts its heat towards the ice at less than 0oC, so it melts quickly
The wood does not conduct it heat and insulated it instead.
