P7

What are the different types of energy (8 types)

Kinetic- anything moving
Thermal- Hotter object, more energy
Chemical- Food, fuels
GPE- anything in gravitational field
EPE- Stretched rubber bands etc
Magnetic- Magnets attracting each other
Electrostatic- Charges repelling each other
Nuclear- Atomic nuclei releasing energy

4 main ways energy can be transferred and how it is expressed

Mechanically- Object moving due to force acting upon it
Electrically- Charge moving through a voltage
Heating- Energy transferred from hotter to colder object
Radiation- Energy transferred by light/sound

Must state energy type and object possessing the energy

What is work?

Work- process of transferring one energy store to another

What is Mechanical work and how to calculate it

Mechanical work only done by the force acting in direction of distance travelled

Work done = force x distance

What is gravitational potential energy and how to calculate it

Amount of energy stored in object due to its height above the ground

GPE = Mass x gravity x height

What is Hooke’s Law?

Extension of an elastic device (eg. spring) is directionally proportional to applied force

Force = spring constant x extension

What is elastic potential energy and how to calculate it

EPE is energy stored in spring which has been extended or compressed from its original length

Work = ½ x spring constant x extension²

What are the rules surrounding conservation of mechanical energy?

Energy can’t be created nor destroyed, can only change from one type to another

In a closed system, sum of potential and kinetic energy is same at all points in an object’s motion

½ mv² + mgh = E
mgh₁ + ½ mv²₁ = mgh₂ + ½ mv²₂

Difference between heat and temperature

Heat is the change in thermal energy (Total KE of particles in a substance) whilst temp. is the measure of average KE in a substance

How to calculate SHC and SLH

Heat energy = mass X SHC x Temp. change
E = m x SHC x change in T

Energy = SLH x mass
E = m x SLH

How do you find the SHC of water (6 marks)

1. Measure mass of water using top pan balance by measuring mass of measuring cylinder and subtract that from total mass
2. Measure initial temp using thermometer Fully submerge heater in water then find power of electrical heater using P=IV (voltmeter parallel and ammeter in series)
3. Find energy using E=PxT
4. Find temp change by using a thermostat and subtracting initial from final temp. after heating for 10 mins
5. Calculate SHC of water by doing E/(m x temp. change)

What is Energy Dissipation

When energy is transferred from one store to another, some of the energy is dissipated (no longer useful)

Can be reduced due to friction by using a lubricant

Reduced due to heating by using an insulator

What is conduction

Heat transfer in solids

Transfers kinetic energy from one particle to the next.

Always transfers energy from hotter temperature to colder temperature

Free electrons transfer energy rapidly so metals are good conductors

What is convection

Occurs when gases and liquids are heated

Particles gain kinetic energy and move further apart

Less dense hotter fluid rises- starting a convection current

What is radiation when heating

When infrared radiation (electromagnetic waves) carries heat energy from one place to another

Only way heat energy can travel through empty space (a vacuum)

What is Thermal Conductivity

The measure of a material’s ability to conduct heat

Higher the thermal conductivity, higher rate of energy transfer by conduction across material

How can you reduce heat loss

Can be reduced by using an insulator

Energy transfer through layer of insulating material depends on:

• Temp difference across material

• Thickness of material

• Thermal conductivity of material

Good insulators have low thermal conductivity and thick layers

How does cavity wall insulation reduce amount of heat loss (6 Marks)

1. Heat conducted through walls of home

2. Air has low thermal conductivity so reduces conduction

3. Air would convert heat to outer wall

4. Foam insulation traps air in little pockets preventing convection currents

5. Inner wall would radiate energy in form of IR to outer wall

6. Shiny foil reflects IR energy back to inner wall

What are the different equations for power

P = IV

P = I²R

P = V²R

P = E/T

How to calculate Energy use in the home

Energy = Power x timr

Total cost = units of energy used (eg. kWh) x price per unit of energy

Properties of Sankey diagrams

Energy input from left

Useful energy output out the right

Wasted or unwanted energy goes down

Width represents amount of energy but length has no significance