energy (p1)

Question 1

describe elastic potential energy:

Answer 1

• when stretching the spring, we’re applying a force to change the length
• this is called ‘doing work’
• we’re putting energy in to stretch the spring. the spring is storing the energy. this is called elastic potential energy
• the spring’s extension and the force applied is directly proportional. however, applying too much force to the spring will make it reach its limit of proportionality, where it can’t stretch anymore

Question 2

define ‘work done’:

Answer 2

energy transferred when a force is used to move an object over a distance
- essentially, work is done when energy is transferred from one store to another

Question 3

describe gravitational potential energy:

Answer 3

• the energy stored in an object due to its position above the Earth’s surface
• this is from the force of gravity acting on the object

Question 4

define specific heat capacity:

Answer 4

the energy required to raise the temperature of 1kg of a substance by 1 degree celsius

Question 5

define power:

Answer 5

• power is the rate at which energy is transferred or at the rate at which work is done
• power is measured in watts.
• an energy transfer of one joule per second is equal to 1 watt.

Question 6

what is the law of conservation of energy?

Answer 6

energy can be transferred usefully, stored or dissipated, but it cannot be created or destroyed

Question 7

describe the relationship between thermal conductivity and energy transfer:

Answer 7

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

Question 8

name three ways to prevent a house from becoming thermally conductive:

Answer 8

• walls are made out of an external brick wall and an internal breezeblock. this is very thermally conductive, so the cavity in the middle is packed with insulation
• double glazed windows as opposed to single glazed windows
• loft insulation

Question 9

define efficiency:

Answer 9

a comparison of the power output to the energy input in a given system

Question 10

what is a renewable energy source?

Answer 10

• an energy source that is being (or can be) replenished as it is being used.

Question 11

name some uses of energy sources:

Answer 11

• transport
• electricity
• generation
• heating

Question 12

evaluate the use of fossil fuels:

Answer 12

advantages:
- reliable
- release a great deal of energy (e.g. good for aeroplanes)
- abundant and relatively cheap
- versatile (very useful for powering vehicles)

disadvantages:
- releases carbon dioxide (climate change)
- non-renewable
- can release other pollutants (e.g. diesel releases carbon particles and nitrogen oxides)

Question 13

describe nuclear power:

Answer 13

• non-renewable, runs on plutonium and uranium
• once running, doesn’t release co2; extremely reliable
• contains highly dangerous radioactive materials; decommission takes ages and is expensive
• generates electricity

Question 14

evaluate renewable energy resources:

Answer 14

advantage:
- renewable (obviously)
- don’t release carbon dioxide

disadvantage:
- wind and solar aren’t reliable
- hydroelectric is reliable but destroys habitats when built

Question 15

describe bio-fuels:

Answer 15

• other renewable energy sources only generate electricity, and we cannot always use this for transport
• biofuels are produced from plant materials, and don’t add co2 to the climate (carbon neutral)
• however, to grow the crops to create bio-fuels, it will take up food growing space, which may increase the price of food even more

Question 16

what is a system?

Answer 16

a system is an object or a group of objects.
- e.g. in a pendulum, the objects in the system would be the mass, string, and the fixed point at the top. air particles could also be considered part of the system.

Question 17

describe the forces acting on an object when it is moving, then it hits an obstacle:

Answer 17

• initially has a lot of kinetic energy, allowing it to move.
• when it hits the obstacle, the kinetic energy is immediately transferred into other stores, such as thermal energy and sound waves to the surroundings.

Question 18

describe the forces acting on an object when it is being accelerated by a constant force:

Answer 18

• energy is required to accelerate the object (chemical, thermal, electrical).
• this energy will then gradually convert into kinetic energy, gradually increasing the velocity of the object, therefore accelerating it.

Question 19

what is the equation for kinetic energy?

Answer 19

• kinetic energy = 0.5 x mass x (speed)^2
• kinetic energy = joules (J)
• mass = kilograms (kg)
• speed = m/s

Question 20

what is the equation for gravitational potential energy?

Answer 20

• G.P.E = mass x gravitational field strength x height
• G.P.E = joules (J)
• mass = kilograms (kg)
• height = metres (m)
• gravitational field strength = newtons per kilogram (N/kg)

Question 21

what is the equation for specific heat capacity?

Answer 21

• change in thermal energy = mass x specific heat capacity x temperature change
• change in thermal energy = joules (J)
• mass = kilograms (kg)
• specific heat capacity = joules per kilogram degrees celsius
• temperature change = degrees celsius)

Question 22

what are the two equations for power?

Answer 22

1. power = energy transferred / time
2. power = work done / time

• power = watts (W)
• energy transferred = joules (J)
• time = seconds (s)
• work done = joules (J)

Question 23

give an example to describe power:

Answer 23

• consider a weight-lifting scenario.
• two individuals lift the same weight over their heads, but one does it faster than the other, the one who lifted the weight more swiftly has exerted more power.
• they have done the same amount of work in less time, hence, they have a higher power output.

Question 24

describe energy transfers in a closed system:

Answer 24

• energy can be transferred in a closed system.
• since energy cannot exchange with the surroundings, there will be no net change with the total energy in the system.
• e.g. adding ice cubes to a bottle of water and closing the lid is an energy transfer.
• assuming the water bottle doesn’t exchange any energy with its surroundings, and that it’s a closed system
• the water will exchange thermal energy with the ice cubes, so the water will cool down.

Question 25

describe lubrication as a method of reducing unwanted energy transfer:

Answer 25

• energy can be lost due to friction.
• when riding a bike, the chain will produce a lot of friction.
• in order to combat this, place oil (a lubricant) on the chain.
• this will stop the chain from experiencing so much friction, and will maintain the bike in the long run.

Question 26

describe streamlining as a method of reducing unwanted energy transfer:

Answer 26

• when objects travel through the air, they experience a contact force called air resistance.
• to combat this, we streamline objects.
• changing the shape of an object streamlines it, meaning it doesn’t feel the effects of air resistance as much.
• e.g. aeroplanes have ‘pointy’ noses.

Question 27

what are the equations for efficiency?

Answer 27

1. efficiency = useful output energy transfer / total input energy transfer
2. efficiency = useful power output / total power input

Question 28

what are the main energy resources available for use on Earth (11, 3 of which are fossil fuels):

Answer 28

• fossil fuels: coal, oil, gas
• nuclear fuel
• bio-fuel
• wind
• hydro-electricity
• geothermal
• tidal
• solar
• waves

Question 29

describe the patterns and trends in the use of energy resources:

Answer 29

• over the past 20 years, there has been a gradual shift towards cleaner technologies.
• government grants have encouraged the use of wind and solar energy farms.
• coal has gradually been replaced with cleaner natural gas.
• a new gen of nuclear power stations is currently in development.