Energy part 2

Question 1

When do systems warm up ?

Answer 1

Systems warm up when energy is transferred to their thermal energy store.

Question 2

When do systems cool down ?

Answer 2

Systems cool down when energy is transferred out of their thermal energy store.

Question 3

What do some systems need that others don’t?

Why is this ?

Answer 3

Some systems need more energy than others to warm up.

This is because they are made of different substances.

Question 4

For example 👉

Answer 4

For example, it takes 130 J of energy to raise the temperature of 1 kg of gold by 1°C.
But it takes 4200 J of energy to raise the temperature of 1 kg of water by 1°C.

Question 5

What 2 things does this mean ?

Answer 5

This means that 1 kg of gold will warm up faster than 1 kg of water.
However, it also means that 1 kg of water can store more thermal energy than 1 kg of gold.

Question 6

What has a specific heat capacity ?

Answer 6

Every substance has a specific heat capacity.

Question 7

What is the specific heat capacity ?

Answer 7

This is the amount of energy it takes to raise the temperature of 1 kg of that substance by 1°C.

Question 8

How many joules of energy does it take to raise the temperature of 1 kg of water by 1°C?
So what is the specific heat capacity of water ?
Units

Answer 8

it takes 4200 J of energy to raise the temperature of 1 kg of water by 1°C.So the specific heat capacity of water is 4200 J/kg°C.

Question 9

What is specific heat capacity measured in ?

Answer 9

Specific heat capacity is measured in joules per kilogram per degree Celsius

Question 10

When can calculate the amount of thermal energy stored in a system ?

Answer 10

You can calculate the amount of thermal energy stored in a system after warming or cooling

Question 11

For example, calculate the change in thermal energy when 0.5 kg of water is heated from 20°C to 50°C.

Answer 11

63,000J

Question 12

What has happened in this example to the water ?

Answer 12

In this example, the water has gained energy in its thermal energy store.

Question 13

For example, calculate the change in thermal energy when 0.5 kg of water cools from 20°C to 5°C.

Answer 13

-31,500J

Question 14

What has happened in this example to the water ?

Answer 14

In this example, the water would lose energy from its thermal energy store.

Question 15

👉why is this ?

Answer 15

This is because the change in temperature and the change in thermal energy are negative.

Question 16

What is power ?

Answer 16

Power is the rate of energy transfer.

Question 17

In other words ?

Answer 17

In other words, power is the rate at which work is done.

Question 18

What is power measured in ?

Answer 18

Power is measured in watts (W).

Question 19

What is one watt equal to ?

Answer 19

1 watt is equal to an energy transfer of 1 joule per second.

Question 20

For example …

Answer 20

For example, a hair dryer might have a power of 1500 W.

This means that when it is switched on, it transfers 1500 joules of energy every second.

Question 21

For another example …

Answer 21

A wind turbine has a much higher power of around 1.5 MW (megawatts).
This means that it can transfer energy much faster, at a rate of 1 500 000 joules every second.

Question 22

What is the equation for power?

Answer 22

Power (W)= energy transferred
——————————
Time

Power(W)= work done
————————
Time

Question 23

For example, an electric scooter has energy in its battery’s chemical energy store.
When it is switched on, some of this energy is transferred to the scooter’s kinetic energy store.what is this energy ?
Why?

Answer 23

This energy is useful energy

This is a useful transfer because it makes the scooter move.

Question 24

What is this called when energy is wasted?

What does this mean?

Answer 24

Energy is dissipated.

This means it is transferred to less useful energy stores.Like the thermal energy stores.

Question 25

What is a closed system ?

Answer 25

A closed system is a system where energy cannot enter or leave.

Question 26

What can happen to energy in a closed system ?

Answer 26

Energy can only be transferred usefully, stored, or dissipated by the objects within the system.

Question 27

What happens to the total amount of energy in a system ? | Give an example?

Answer 27

The total amount of energy in a closed system always stays the same. The total amount of energy in the entire universe always stays the same.

Question 28

What can we think of as a closed system?

Answer 28

We can think of the entire Universe as a closed system

Question 29

What is the purpose of lubricants?

Answer 29

Lubrication helps to prevent energy being wasted.

Question 30

When is energy dissipated ? | What is this often called?

Answer 30

In all system changes, some energy is dissipated. | This energy is often called "wasted energy".

Question 31

What is one way to reduce the amount of energy that a system wastes.How do you use this?

Answer 31

One way is by using lubrication. | Lubrication usually involves spreading an oily substance over the parts of a mechanical system.

Question 32

What is the main purpose of lubricants? | What will this mean?

Answer 32

This reduces the friction between objects when they move. This means more energy is transferred into useful kinetic energy stores. And less energy is transferred into thermal energy stores.

Question 33

How can thermal energy be transferred ?

Answer 33

Thermal energy can be transferred through conduction.

Question 34

What happens in conduction?

Answer 34

In conduction, vibrating particles transfer energy to their neighbouring particles.

Question 35

👉what does this allow them to do ?

Answer 35

This allows energy to spread across the entire length of a material.

Question 36

What does thermal conductivity measure ?

Answer 36

Thermal conductivity is a measure of how quickly a material can transfer energy by conduction.

Question 37

What happens the higher a material's thermal conductivity?

Answer 37

The higher a material's thermal conductivity, the faster energy is transferred And the faster the material heats up (and cools down).

Question 38

What do thermal insulators do?

Answer 38

Thermal insulation helps to prevent energy being wasted by conduction.

Question 39

Why are buildings often heated ?

Answer 39

Buildings are often heated so that they are warm enough to live and work in.

Question 40

How does buildings lose their heat?

Answer 40

However, the buildings lose this heat to their surroundings.

Question 41

What two things does the rate of cooling depend on?

Answer 41

One is the thickness of the building's walls. The thinner the walls, the faster energy can be transferred through them. Another factor is the thermal conductivity of the building's walls.

Question 42

How would you transfer more energy to the outside ?

Answer 42

Walls made of materials with a high thermal conductivity will transfer more thermal energy to the outside.

Question 43

What do many buildings use and why ?

Answer 43

Many buildings use thermal insulation to reduce the rate of cooling.

Question 44

👉Give an example

Answer 44

One example is an air gap between two walls, filled with a poor conductor like foam.

Question 45

How do you calculate efficiency ?

Answer 45

Useful output energy transfer Efficiency =———————————— Total input energy transfer

Question 46

What equation can you use if you know a system's power input and output ?

Answer 46

Useful power output Efficiency =___________________ Total power input

Question 47

Why are systems never 100% efficient ?

Answer 47

Remember, systems are never 100% efficient, because only some energy is usefully transferred, while the rest is dissipated.

Question 48

What will reducing the amount of dissipated energy do ?

Answer 48

Reducing the amount of dissipated energy will increase the efficiency of the energy transfer.

Question 49

How do you know Reducing the amount of dissipated energy will increase the efficiency of the energy transfer ?(give an example )

Answer 49

For example, thermal insulation increases the efficiency of heating houses. This is because it can reduce the amount of energy lost through a house's walls to the surroundings.