P1 - Energy (4.1.1 (Power (Power is defined as the rate at which energy is…
P1 - Energy
Energy stores and systems
A system is an object or group of objects
There are changes in the way energy is stored when a system changes
Example of changes to a system
bringing water to a boil in an electric kettle
Changes in Energy
kinetic energy(J) = 0.5 x Mass(kg) x (Speed(m/s))^2
elastic potential energy(J) = 0.5 x spring constant(N/m) x (extension(m))^2
gravitational potential energy = Mass(kg) × Gravitational Strength(N/kg) × Height(m)
Energy changes in systems
Change in Thermal Energy (J) = Mass(kg) x Specific Heat Capacity(J/Kg °C) x Tempreture Change (°C)
The specific heat capacity of a substance is the amount of energy required to raise the temperature of one kilogram of the substance by one degree Celsius.
Power is defined as the rate at which energy is transferred or the rate at which work is done.
Power(W) = Energy Transferred(J) / Time(s)
Power(W) = Work Done (J) / Time (s)
An energy transfer of 1 joule per second is equal to a power of 1 watt.
Energy transfers in a system
Energy can be transferred usefully, stored or dissipated, but cannot be created or destroyed.
in all system changes energy is dissipated, so that it is stored in less useful ways. This energy is often described as being ‘wasted’.
The higher the thermal conductivity of a material the higher the rate of energy transfer by conduction across the material.
ways of reducing unwanted energy transfers, for example through lubrication and the use of thermal insulation
efficiency = useful output energy transfer / total input energy transfer
Efficiency = Useful output energy / Total power input
Energy Resources: fossil fuels (coal, oil and gas), nuclear fuel, biofuel, wind, hydro-electricity, geothermal, the tides, the Sun and water waves.
A renewable energy resource is one that is being (or can be) replenished as it is used.
The uses of energy resources include: transport, electricity generation and heating