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Physics - Paper 1 > Energy part 2 > Flashcards

Energy part 2 Flashcards

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1
Q

When do systems warm up ?

A

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

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2
Q

When do systems cool down ?

A

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

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3
Q

What do some systems need that others don’t?

Why is this ?

A

Some systems need more energy than others to warm up.

This is because they are made of different substances.

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4
Q

For example 👉

A

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.

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5
Q

What 2 things does this mean ?

A

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.

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6
Q

What has a specific heat capacity ?

A

Every substance has a specific heat capacity.

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7
Q

What is the specific heat capacity ?

A

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

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8
Q

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

A

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.

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9
Q

What is specific heat capacity measured in ?

A

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

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10
Q

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

A

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

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11
Q

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

A

63,000J

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12
Q

What has happened in this example to the water ?

A

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

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13
Q

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

A

-31,500J

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14
Q

What has happened in this example to the water ?

A

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

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15
Q

👉why is this ?

A

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

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16
Q

What is power ?

A

Power is the rate of energy transfer.

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17
Q

In other words ?

A

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

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18
Q

What is power measured in ?

A

Power is measured in watts (W).

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19
Q

What is one watt equal to ?

A

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

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20
Q

For example …

A

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.

21
Q

For another example …

A

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.

22
Q

What is the equation for power?

A

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

Power(W)= work done
————————
Time

23
Q

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?

A

This energy is useful energy

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

24
Q

What is this called when energy is wasted?

What does this mean?

A

Energy is dissipated.

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

25
Q

What is a closed system ?

A

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

26
Q

What can happen to energy in a closed system ?

A

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

27
Q

What happens to the total amount of energy in a system ?

Give an example?

A

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.

28
Q

What can we think of as a closed system?

A

We can think of the entire Universe as a closed system

29
Q

What is the purpose of lubricants?

A

Lubrication helps to prevent energy being wasted.

30
Q

When is energy dissipated ?

What is this often called?

A

In all system changes, some energy is dissipated.

This energy is often called “wasted energy”.

31
Q

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

A

One way is by using lubrication.

Lubrication usually involves spreading an oily substance over the parts of a mechanical system.

32
Q

What is the main purpose of lubricants?

What will this mean?

A

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.

33
Q

How can thermal energy be transferred ?

A

Thermal energy can be transferred through conduction.

34
Q

What happens in conduction?

A

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

35
Q

👉what does this allow them to do ?

A

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

36
Q

What does thermal conductivity measure ?

A

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

37
Q

What happens the higher a material’s thermal conductivity?

A

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

38
Q

What do thermal insulators do?

A

Thermal insulation helps to prevent energy being wasted by conduction.

39
Q

Why are buildings often heated ?

A

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

40
Q

How does buildings lose their heat?

A

However, the buildings lose this heat to their surroundings.

41
Q

What two things does the rate of cooling depend on?

A

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.

42
Q

How would you transfer more energy to the outside ?

A

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

43
Q

What do many buildings use and why ?

A

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

44
Q

👉Give an example

A

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

45
Q

How do you calculate efficiency ?

A

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

46
Q

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

A

Useful power output
Efficiency =___________________
Total power input

47
Q

Why are systems never 100% efficient ?

A

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

48
Q

What will reducing the amount of dissipated energy do ?

A

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

49
Q

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

A

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.

Physics - Paper 1 (9 decks)

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