P1 and P2

Question 1

what is the law of conservation of energy:

Answer 1

– Energy cannot be created or destroyed, only transferred into another type of energy

Question 2

List all the energy stores and what they do:

Answer 2

– Chemical energy: energy is transferred during a chemical reaction
- Kinetic energy: the energy an object has because it is moving
– Gravitational potential energy: an objects position changes, it moves higher
– Elastic potential energy: energy stored in a springy objects when you stretch or squash it
– Thermal energy: energy a substance has due to its temperature

Question 3

What is a closed system?

Answer 3

• A system in which no energy transfers take place out of or into the energy stores of the system
• A sytem is an object or a group of objects

Question 4

how can energy be transferred?

Answer 4

• by heating
• by waves
• by an electric current
• by a force when it moves an object

Question 5

what is the equation for work done (energy transferred)?

Answer 5

Work done = Force applied X Distance moves (along the line of action of the force)

W = F x S
W = Joules
F = Newtons
S = Metres

Question 6

what is the equation for weight?

Answer 6

weight = mass x gravitational field strength
W = M x G

W = newtons (n)
M = kilograms (kg)
G = newtons per kilogram (N/kg)

Question 7

how does the gravitational potential energy of an object change as you move it up and down?

Answer 7

• when it moves up the gravitational potential energy increases
• when it moves down the gravitational potential energy decreases

Question 8

Why can objects be lifted much more easily at the moon than on earth?

Answer 8

-Because the gravitational field strength at the surface of the moon is less than on the earth

Question 9

What is the equation for the change of gravitational potential energy store of an object?

Answer 9

gravitational potential energy = mass X gravitational field strength X height

Ep = M x G x H

Ep = joules (j)
M = mass (kg)
G = newtons per kilogram (N/kg)
H = metres (m)

Question 10

What is the equation for kinetic energy?

Answer 10

kinetic energy = 1/2 x Mass x Speed2(squared)

Ek = 1/2 x M x V2(squared)

Ek = joules (j)
M = kilograms (kg)
V2 = metres per second (m/s)2(squared)

Question 11

What is the equation for elastic potential energy?

Answer 11

elastic potential energy = 1/2 x Spring constant x extension2(squared)

Ee = 1/2 x K x e2(squared)

Ee= joules (j)
K = newtons per metre (N/m)
e2(squared) = metres2 (m2)

Question 12

what is useful energy?

Answer 12

-energy in the place we want it and in the form we need it

Question 13

what is wasted energy?

Answer 13

• the energy that is not useful energy and it transferred by an undesired pathway
• wasted energy is eventually transferred to the surroundings which become warmer

Question 14

what is dissipation of energy?

Answer 14

-energy spreads out and gets less and less useful

Question 15

what is the equation for efficiency?

Answer 15

efficiency (%) = useful output energy transferred by the device (j)/ total input energy supplied to the device (j) (x 100%)

Question 16

how do machines waste energy?

Answer 16

• friction between their moving parts
• air resistance
• electrical resistance
• noise

Question 17

how to reduce friction between moving parts which causes heat?

Answer 17

-lubricate moving parts to reduce friction

Question 18

how to reduce electrical resistance of wires which causes wires to heat up?

Answer 18

-use wires with as little electrical resistance as possible

Question 19

how to reduced sound from machine which cause energy transfer to surroundings?

Answer 19

-cut out noise (e.g. tighten loose parts to reduce vibration)

Question 20

what is the equation for power of an appliance?

Answer 20

Power, P = energy transferred to appliance, E/ time taken for energy to be transferred, T

P = Watts (w)
E = Joules (j)
T = Seconds (s)

Question 21

What is power?

Answer 21

-rate of energy transferred per second

Question 22

what is the equation for power efficiency of an appliance?

Answer 22

efficiency = useful power out/ total power in (x100%)

Question 23

what is the equation for wasted power?

Answer 23

power wasted = total power in - useful power out

Question 24

what materials make the best conductors of energy?

Answer 24

-Metals

Question 25

what materials make the best insulators?

Answer 25

-non-metal materials such as wool and fibreglass

Question 26

how does thermal conductivity and insulation affect the rate of energy transfer?

Answer 26

- the higher the thermal conductivity of a material, the higher the rate of energy transfer through it - the thicker a layer of insulating material, the lower the rate of energy transfer through it

Question 27

what is the specific heat capacity of a substance?

Answer 27

-the amount of energy needed to raise the temperature if 1kg of the subtance by 1C

Question 28

what is the equation for specific heat capacity?

Answer 28

specific heat capacity = energy transferred/ mass x temperature change Or energy transferred = mass X specific heat capacity X temperature change energy transferred = E (joules, j) mass = M (kilograms, kg) specific heat capacity = C (joules per kilogram per degree celsius, J/kgC) temperature change = (Celsius, C)

Question 29

how can the rate of energy transfer from houses be reduced?

Answer 29

- loft insulation - cavity wall insulation (material used to fill gaps betwem two brick layers) - double-glazed windows - aluminium foil behind radiators - external walls with thicker bricks and lower thermal conductivity