Energy changes in a system (1.1) (M)

Question 1

What are the nine types of energy?

Answer 1

Kinetic, sound, light, thermal, electrical, gravitational potential, elastic potential (strain), chemical, nuclear

Question 2

What is a system?

Answer 2

an object or group of objects

Question 3

What happens to energy when a system is changed?

Answer 3

there are changes in the way energy is stored

Question 4

3 ways

How may energy be transferred?

Answer 4

• heating
• work done by forces
• work done when a current flows

also may be by radiation (e.g. light, microwaves, sound)

Question 5

How is energy transferred when an object is projected upwards?

Answer 5

Chemical energy store of body to GPE store of object due to work done by forces

Question 6

How is energy transferred when a moving object hits an obstacle?

Answer 6

Kinetic store of object to thermal/elastic potential of obstacle due to work done by forces

Question 7

How is energy transferred when an object is accelerated by a constant force e.g. car accelerating?

Answer 7

chemical store of fuel to kinetic store of object due to work done by forces

Question 8

How is energy transferred when a vehicle slows down?

Answer 8

kinetic store of vehicle to thermal store of brakes and surroundings due to work done by forces

Question 9

How is energy transferred when water is brought to a boil in an electric kettle?

Answer 9

chemical store of fuel (at power station) to thermal store of water due to work done when a current flows

Question 10

e.g. mass

Energy in a system may be dependant on what?

Answer 10

• mass
• velocity
• elasticity
• gravitational potential energy
• height from ground
• temperature
• etc

There is no definitive list, these are purely examples. Just make sure in an exam if a question like this was asked, to look at the equation list

Question 11

What is spring constant?

Answer 11

A measure of the stiffness of the spring

Question 12

What is specific heat capacity of a substance?

Answer 12

The amount of energy required to raise the temperature of 1kg of the substance by 1^oC

Question 13

Why might not all energy be transferred when a substance is heated?

Answer 13

Thermal energy is lost to the surroundings

Question 14

When heated (without changing state), energy is transferred from what store to another?

Answer 14

Potential to Kinetic (thermal)

Question 15

What is power?

Answer 15

the rate at which energy is transferred or the rate at which work is done

Question 16

What is the power of 1 watt equivalent to?

Answer 16

An energy transfer of 1 joule per second

Question 17

Two electric motors lift both the same weight through the same height but one does it faster than the other, why is this?

Answer 17

Because one electrical motor has a greater power (i.e. energy is transferred quicker)

Question 18

What does one object having a greater power than the other mean?

Answer 18

It transfers energy quicker

Question 19

What is conduction?

Answer 19

How heat transfers in a solid

Question 20

What is convection?

Answer 20

How heat transfers in liquids and gases

Question 21

How does heat transfer through glass?

Answer 21

Thermal energy applied

Particles vibrate in solid

Particles that they are touching also vibrate, transferring thermal energy

Question 22

How does conduction occur in metal? (answer in terms of electrons)

Answer 22

When heated, free electrons gain kinetic energy.

These electrons transfer kinetic energy to other electrons by collision

Question 23

How is a convection current created?

Answer 23

when heat is applied

air particles spread out

which causes the air to come less dense

so warm air rises

(gap filled by cooler air)

Question 24

When speed or distance over a given time double, by what amount does work done / kinetic energy increase by?

Answer 24

A factor of 4

• this is because of the equation, follow the maths steps:*
• E_k = ½ x m x v²*
• Double v: E_k = ½ x m x (2v)²*
• E_k = ½ x m x 4v²*
• also speed = distance / time*

Question 25

4 marks

Explain, in terms of particles. how evaporation causes cooling of water

Answer 25

Fastest particles have enough energy to leave the surface

To leave the surface of the water

Therefore, mean energy of remaining particles decreases

The lower the mean energy of particles, the lower the temperature of the surface

Question 26

How does conduction occur in a metal? (answer in terms of atoms)

Answer 26

Thermal energy is applied to the metal

Atoms gain kinetic energy and vibrate, when they do this they transfer kinetic energy to neighbouring particles (making them vibrate) by collision

until kinetic energy is spread equally through the whole metal

Question 27

3 marker - key - learn to adapt

The power output of a turbine is directly proportional to the kinetic energy of the air passing the blade each second.

What is the effect on power output when the wind speed is halved?

Answer 27

Mass of air passing turbines is halved which decreases kinetic energy by a factor of 2

(wind speed is halved) which decreases the kinetic energy by a factor of 4

so kinetic energy decreases by a factor of 8

allow power output for kinetic energy throughout

Question 28

What does it mean for a device to be efficient?

Answer 28

Most input energy is usefully transformed (with not a lot of waste energy)