1) Introduction to Thermal Physics

Question 1

What are watts (W)

Answer 1

Watts are a measurement of power, describing the rate at which electricity is being used at a specific moment.

Question 2

How many watts are in a kilowatt (kW)

Answer 2

1000

Question 3

How many watts are in a megawatt (MW)

Answer 3

1,000,000

Question 4

How many watts are in a gigawatt (GW)

Answer 4

1,000,000,000

Question 5

How many kilowatts (kW) are in a gigawatt (GW)

Answer 5

1,000,000

Question 6

Convert °C to K

Answer 6

K= °C + 273

Question 7

What is absolute 0?

Answer 7

-273 °C, where particles have absolutely zero kinetic energy.

Question 8

The formula for pressure?

Answer 8

Pressure=Force/Area
Pa= N/m²

Question 9

What is ‘work done’?

Answer 9

Work is done when energy is transferred from one place to another.

(E.g. when a box is lifted, work is done, and energy is transferred from the person lifting, to the box)

Question 10

A car has an energy input of 50,000J.
Energy output-
Heat-7000J
Light- 0J
Sound- 300J
Kinetic- 42700J

Calculate the efficiency

Answer 10

0.854

Question 11

What is the law of conservation of energy?

Answer 11

Energy can neither be created nor destroyed - only transferred from one energy store to another

Question 12

What is the first law of thermodynamics

Answer 12

It states that the total energy of a closed system remains constant.

Question 13

What is the formula for the first law of thermodynamics?

Answer 13

ΔU=Q−W

ΔU= Change in internal energy (of the system)
Q= Heat applied (to the system)
W= Work done (by the system)

Question 14

What is the definition of internal energy (U)?

Answer 14

Sum of randomly distributed kinetic and potential energy

Question 15

What is an adiabatic process?

Answer 15

Temperature does change during the process. Process is too fast for heat energy to escape.

Question 16

What is an isothermal process?

Answer 16

Temperature does not change during the process. Process is slow enough for heat energy to escape to surroundings.

Question 17

Give an example of when both adiabatic and isothermal process are demonstrated.

Answer 17

A fire piston is a closed cylinder with a plunger and a piece of flammable tinder. When the plunger is struck hard and quickly a flame can be made at the bottom of the cylinder (adiabatic). When the plunger is pressed too slowly then no flame will be generated (isothermal)

Question 18

Explain why a bicycle pump gets warm when you pump tyres to quickly

Answer 18

Pumping compresses the air very quickly, so even without insulation the process is near adiabatic. This means all the work is transformed into increased internal energy ad hens higher temp in the gas.

Frictional and viscous forces means that extra work is being done, which also converts directly into het, and raises the temperature more.

Question 19

What is the Carnot cycle?

Answer 19

A Carnot cycle is an ideal reversible closed thermodynamic cycle. Four successive operations are involved: isothermal expansion, adiabatic expansion, isothermal compression, and adiabatic compression.

Question 20

What is the Otto cycle?

Answer 20

The Otto cycle is a cycle of engine operation which requires four strokes of the piston: for induction, compression, ignition, and exhaust.

Question 21

What is the Diesel cycle?

Answer 21

The diesel cycle has heat applied at a constant pressure (aka constant pressure cycle)

It has four stages:
compression, combustion,
expansion, and cooling.

Question 22

What is the Rankine cycle?

Answer 22

The Rankine cycle is an idealized thermodynamic cycle describing the process by which certain heat engines allow mechanical work to be extracted from a fluid as it moves between a heat source and a heat sink.

Question 23

What is the 2nd law of thermodynamics?

Answer 23

It states that systems will tend towards disorder. Some consequences of this law are that heat flows from hot regions to cold and systems that are ordered will become disordered over time.

Further implications of this law mean that it is impossible for a system to be 100% efficient, some energy is always lost or wasted. This forbids perpetual motion machines.

Question 24

What is a heat engine?

Answer 24

A heat engine is a device which allows heat to flow from a hot reservoir to a cold reservoir and uses some of the heat to produce mechanical work in the process.

Question 25

What is a heat pump?

Answer 25

A heat pump is a device that moves heat from a cold place to a hot place. A refrigerator is an example of a heat pump.

Question 26

What 4 parts does a refrigerator consist of?

Answer 26

-Compressor
-Condensers coils
-Expansion device
-Evaporator coils

Question 27

What is the hottest and coldest part of the cycle in the refrigerant?

Answer 27

Hottest- When it leaves the compressor
Coldest- When it leaves the expansion device.

Question 28

Which part is the refrigerant under the highest pressure

Answer 28

Condenser

Question 29

Which part of the cycle is the refrigerant a gas and which parts is it a liquid?

Answer 29

Condenser + Expansion device- Liquid
Evaporator + Compressor- Gas

Question 30

What is the component that ‘does the work’ in a refrigerator?

Answer 30

The compressor