P2 Specific Heat Capacity Flashcards
What is specific heat capacity?
A way of saying how much energy (hard) is needed to heat something
The amount of energy needed to raise the temprature of 1Kg of a substance 1Cº
What do we know about materials with a high heat capacity?
They will emit heat well
They can “store” a lot of energy
How do you calcuate energy transfered?
ΔE = mcΔθ
Change in thermal energy (Jouls) = Mass (kg) X Specific heat capacity (j/kgºC) X change in tempreture (ºC)
What is the conservation of energy?
Energy can’t be created or destroyed, only transfered between stores ussefully or dissipated
When energy is transfered some of it will always be…
Dissipated to things like air resistance or friction
This is sometimes known as wasted energy
On a mobile phone wasted energy is the thermal stores
What happens if you drop a spoon in a hot soup in a closed system?
The soup and spoon are in a perfect insulated closed container so no energy is being lost or gained from external means
The usefull thermal energy of the soup is being transfered to the useless thermal store of the spoon. This means that the soup has cooled a bit.
Because this is a closed system the net change in energy =0
What is power?
What is it measured in?
What is always a charatristing of a powerfull machine?
The rate of doing work/ rate of energy transfer
Watts (W)
It will be able to transfer large amounts of energy quickely
How can you calcuate power?
P = E or W ÷ T
Power (Watts) = Energy transfered (Joules) OR Work done (Joules) ÷ Time (Seconds)
How can you reduce the amount of useless energy lost to friction?
Lubrication reduces friction
Nearly everythig that moves disipates energy through friction. Lubrication is usally an oil or liquid which lets things rub together easierly
What is conduction?
Is conduction faster in a gas or solid?
(When an object is heated energy is transfered into the kinetic stores of the particles)
This causes the paritcles to move faster and collode with each other more. When particles collide they transfer energy this is called CONDUCTION
If the particles are in a liquid or gass form there are more space between the particles which leads to less reaction and a lower dencity. This causes heat to decrease.
What is thermal conductivity?
How quickely energy is passed through a material
Something with a high thermal conductivity will heat up fast
What is convection?
Since liquids and gasses can flow a hotter particle will rise and force the colder particles below it. This causes the hotter air to move to colder places in a room.
How can you prevent heat from escaping from a house?
Thick walls made out of a material with a low thermal conductivity
Use thermal insulation:
Cavity walls. Made up of 2 walls which trap air inbetween them. Air has a relativly low thermal conductivity so it works quite well. You may fill the walls with a material like foam which an even lower thermal conductivity
Loft insulation. This can reduce convection currents being created in the loft
Double glazed windows. The same as cavity wallsbut with windows
Draight exculders around the doors and windows. This will decrease heat escaping throguh convection
What is the energy efficency of something?
How can you increase the efficency of something?
How much energy is being used usefully compared to how much energy is being wasted
You can increase efficency by usong things like lubricants or make it more streamlined…
How do you calcuate efficency?
E = U ÷ T
Efficency = Usefull energy transfer ÷ Total energy transfer
This equasion also works with power
