P1: Energy and energy sources

Question 1

What are the 5 different energy stores?

Answer 1

Chemical energy

Kinetic energy

Gravitational potential energy (GPE)

Elastic potential energy

Thermal energy

Question 2

How can energy be transferred?

Answer 2

Energy can be transferred from one store to another by:
1. Heating
2. Waves
3. Electric current
4. When a force moves an object

Question 3

What happens when an object falls and gains speed?

Answer 3

Its gravitational potential (GPE) energy decreases

Its kinetic energy store increases

Question 4

What happens when a falling object hits the ground without bouncing back?

Answer 4

It’s kinetic energy store is transferred:
-> By heating to thermal energy store of the object and its surroundings
-> By sound waves moving away from the point of impact

Question 5

Describe the principle of the conservation of energy?

Answer 5

Energy cannot be created or destroyed

Energy can only be transferred usefully, stored or dissipated

Question 6

What is a ‘closed system’?

Answer 6

An isolated system where no energy transfers take place into or out of the system

Question 7

What can happen to energy within a closed system?

Answer 7

It can be transferred between energy stores within the closed system

Question 8

What happens to the total energy in a closed system when there is transferred?

Answer 8

The total energy of the closed system is always the same before and after any transfers of energy

Question 9

What happens in terms of energy transfers when someone stretches an elastic band?

Answer 9

The chemical store energy in their muscles decreases and is transferred to the elastic potential energy of the elastic band which increases

Question 10

What happens in terms of energy transfers in a pendulum swing?

What happens at the middle? What happens at the end?

Answer 10

When the pendulum is at one end, it’s gravitational potential energy (GPE) is at it’s maximum

When the pendulum swings to the middle it’s gravitational potential energy (GPE) decreases and its kinetic energy is at its maximum

When the pendulum moves away from the middle to the other end, its kinetic energy decreases and the gravitational energy (GPE) increases and is at it’s maximum when it arrives at the end

Question 11

What needs to happen to a stationary object for it to move?

Answer 11

A force needs to be applied to a stationary object to make it move

Question 12

What happens when a force moves an object? what is this called?

Answer 12

When a force moves an object - energy is transferred to an object

We can say that WORK is done on the object

Question 13

What is the work done on an object equal to?

Answer 13

The work done on an object is equal to the energy transferred to the object

Question 14

What is the units for work and energy?

Answer 14

Work and energy are both measured in the same units:

J - Joules

Question 15

How can you work out the work done on an object?

Answer 15

Work done = Force X Distance
W = F S

Where work is measured in J (Joules), Force is measured in N (Newtons) and distance moved is measured in m (metres)

Question 16

How much work is done on an object if it doesn’t move when energy is transferred to it?

Answer 16

No work is done on the object

W = F x 0 (as the distance moved is 0)
Hence
W = 0

Question 17

What force opposes the motion of two surfaces in contact with each other?

Answer 17

Friction

Question 18

What happens to work that is done to overcome friction?

Answer 18

It is mainly transferred to thermal energy stores by heating

Question 19

When does the gravitational potential energy (GPE) of an object change?

Answer 19

It changes due to the objects position in relation to earth’s gravitational field

When an object moves up - its gravitational potential (GPE) increases

When an object moves down - its gravitational potential (GPE) decreases

Question 20

What is the work done when an objects gravitational potential (GPE) energy changes?

Answer 20

When an object moves up, the work done on the object by the lifting force is equal to the increase in gravitational potential energy (GPE)

When an object moves down, the work done on the object by the gravitational force is equal to the decrease in gravitational potential energy (GPE)

Question 21

What is the equation for change in gravitational potential energy when an object is moved up or down?

Answer 21

Δ E = m x g x Δh

Where:
ΔE = Change in GPE measured in J (Joules)
m = mass of the object in kg (kilograms)
g = gravitational strength in N/kg (Newtons per kilogram)
Δh = change in height m (metres)

Question 22

What is the gravitational field strength of earth and of the moon?

Answer 22

The gravitational field strength at earths sufrace = 9.8 N/kg

The moon’s gravitational field strength is 1/6th of the earth’s

Question 23

What energy do all objects that move have?

Answer 23

All moving objects have kinetic energy

Question 24

What is the equation for kinetic energy?

Answer 24

Ek = 1/2 x m x v2

Where:
Ek = Kinetic energy measured in J
m = mass of object measured in kg
v = speed of the object in m/s (metres per second)

Question 25

What two things can increase the kinetic energy has?

Answer 25

Increasing mass Increasing speed

Question 26

What two things can decrease the kinetic energy an object has?

Answer 26

Decreasing mass Decreasing speed

Question 27

What is elastic potential energy?

Answer 27

This is the energy that is stored in an elastic object that has been stretched or squashed

Question 28

When can you describe an object as being elastic?

Answer 28

An object is elastic if it regains its original position after being stretched / squashed

Question 29

What happens when an elastic object is stretched or squashed?

Answer 29

When an elastic object is stretched / squashed the work done on it is stored as elastic potential energy

Question 30

What happens when an elastic object returns to its original shape?

Answer 30

When an elastic object returns to its original position, the energy becomes available for other transfers

Question 31

How can you work out the elastic potential of an object?

Answer 31

Ee = 1/2 x k x e2 Where: Ee = Elastic potential energy in J k = Spring constant of the spring in N/m (Newtons per metre)

Question 32

What do machines do to energy?

Answer 32

They transfer energy for a purpose

Question 33

What is useful energy?

Answer 33

Useful energy is energy that is transferred to where it is wanted, in the form that it is wanted

Question 34

What is wasted energy?

Answer 34

Wasted energy is energy that is either transferred to where it is not wanted or in a form that is not wanted

Question 35

Describe dissipated energy

Answer 35

This is energy that is not usefully transferred and is stored in less useful ways

Question 36

What happens to both useful and wasted energy over time?

Answer 36

Both useful and wasted energy will be transferred into the surroundings and be dissipated - warming up the surroundings

Question 37

What happens as energy dissipates

Answer 37

As energy dissipated as goes further away it becomes harder to use it for future energy transfers

Question 38

How is energy often wasted with moving objects?

Answer 38

Energy is often wasted due to friction with moving object or the moving parts of a machine

Question 39

What happens in terms of energy transfer when a bike / car brakes?

Answer 39

When bike / car brakes: The kinetic energy store of the vehicle decreases and the thermal energy stores of the brakes and surroundings increase

Question 40

What is the energy supplied to a machine called?

Answer 40

The energy supplied to a machine called - input energy

Question 41

What is the energy that is usefully transferred by the machine called?

Answer 41

The energy that is usefully transferred by the machine called - the useful output energy

Question 42

What is the input energy equal to?

Answer 42

According to the principle of the conservation of energy: energy cannot be created or destroyed Hence: Input energy = useful output energy + wasted energy

Question 43

How can a machine be more efficient?

Answer 43

A machine is more efficient if it wastes less energy

Question 44

How can you calculate the efficiency of a device? What are the units?

Answer 44

Efficiency = useful energy transferred ÷ total energy supplied x 100 There are no units as efficiency is a ratio

Question 45

What is the maximum efficiency a machine can have?

Answer 45

The maximum efficiency of a machine is 1 (100%) - it cannot be more than 100% as this would mean that energy out is greater than energy in

Question 46

What are some ways machines can waste energy?

Answer 46

Friction between moving parts Air resistance Electrical resistance

Question 47

How can machines be made more efficient?

Answer 47

Machines can be made more efficient by reducing how much energy they waste

Question 48

How can a machine with moving objects be made more efficient?

Answer 48

Using lubrication decreases friction between the moving objects and makes it more efficient

Question 49

How can a vehicle be made more efficient?

Answer 49

Using a stream-lined design reduces air resistance and makes it more efficient

Question 50

How can electrical devices be made more efficient?

Answer 50

Using copper wires decreases electrical resistance and makes it more efficient

Question 51

What is the only device that can be 100% efficient and why?

Answer 51

A heater as it can transfer all the energy supplied to it as useful heat energy into its surroundings

Question 52

How is most energy in the home supplied as?

Answer 52

Most energy in the home is supplied as electricity, gas or oil

Question 53

What is the useful energy transfer in a: light bulb

Answer 53

Electric energy into light waves emitted from the filament

Question 54

What is the useful energy transfer in a: electric mixer

Answer 54

electric energy into work done by blades of the mixer

Question 55

What is the useful energy transfer in a: speaker

Answer 55

Electric energy into sound waves from vibrations of the speaker

Question 56

What is the useful energy transfer in a: television

Answer 56

Electric energy into light and sound waves

Question 57

What should electrical appliances aim to do in terms of efficiency?

Answer 57

They should aim to waste as little energy as possible and be as efficient as possible

Question 58

What is the power of an appliance?

Answer 58

The power of an appliance is the rate at which it transfers energy

Question 59

What is the unit of power?

Answer 59

Power is measured in Watts (W)

Question 60

What is 1 watt equal to?

Answer 60

1 watt is equal to transferring 1 joule in 1 second 1 W = 1 J/s

Question 61

What can be used to measure power instead of watts and why?

Answer 61

Watts are too small to be useful so power is often measured in kilowatts (kW) Where 1000 W = 1 kW

Question 62

What is the equation for power

Answer 62

P = E / t Where: P = Power measured in W E = Energy transferred in J t = Time measured in s

Question 63

How can you work out power wasted?

Answer 63

Power wasted = total power supplied - useful power output

Question 64

How can efficiency of a device be calculated in relation to power?

Answer 64

efficiency = (useful power output ÷ total power input) x 100