Block 2: Thermal physics

Question 1

What is the temperature of a substance a measure of?

Answer 1

The average kinetic energy of its particles

Question 2

Differences between evaporation and boiling:

Answer 2

evaporations only happens at the surface of a liquid, boiling happens at any point within the liquid
evaporations can happen at any temp, Boiling can only happen at a fixed temp
without a supply of thermal energy boiling stops, while evaporation continues

Question 3

Why is evaporations a cooling process?

Answer 3

Molecules don’t have temperature but kinetic energy so if the kinetic energy is taken away with a molecule as it evaporates then less kinetic energy remains therefore a cooler temperature.

Question 4

What does it mean if a thermometer is sensitive?

Answer 4

There is a large change of physical property for a small change of temperature.

Question 5

Why can a thermocouple measure high temperatures?

Answer 5

because metals have high melting points

Question 6

Why can thermocouples measure very rapidly changing temperatures?

Answer 6

The junctions are very small which means that the temperatures doesn’t affect the measuring tools.

Question 7

What is the difference between internal energy and temperature?

Answer 7

Internal energy is the total energy of all particles (total kinetic and potential energy) while temperature is the measure of the average kinetic energy only of the individual particles.

Question 8

Thermal capacity definition:

Answer 8

How fast a material heats up dependent on their material.

A metal has a low thermal capacity and therefore heats up quickly.

Question 9

Explain the process of evaporation in terms of its molecules

Answer 9

Particles are constantly being pulled down by the liquid so they can’t escape
But some particles have enough kinetic energy to escape to the air as water vapour.
This leaves the liquid with less kinetic energy and therefore cooler.

Question 10

Explain in terms of water molecules, what happens to the thermal energy supplied to water as it boils.

Answer 10

particles absorb energy supplied from heat source- temp rises
molecules gain kinetic energy and overcome forces
faster molecules enter air bubbles in water and become vapour
when big enough bubbles increase to atmospheric pressure and rise to the air

Question 11

Describe an experiment to measure the specific latent heat of steam

Answer 11

1: heat a volume of water to its boiling point
2: measure the mass of the kettle and water on a scale (m2)
3: boil water for three minutes
4: measure the final mass of kettle and water (m1)
5: calculate the mass turned to gas = m1-m2

Question 12

What does it mean if a thermometer has a linear characteristic?

Answer 12

The change of physical property is the same as the change for temperature

Question 13

What does it mean if a thermometer has a linear characteristic?

Answer 13

The change of physical property is the same as the change for temperature

Question 14

What does it mean if a thermometer has a wide range?

Answer 14

There is a large difference between the highest and lowest measurable temperatures.

Question 15

State two properties of alcohol that make it suitable for use in a thermometer:

Answer 15

its a liquid so it expands with heat

it has a high boiling and freezing point

Question 16

State two changes to the design of the thermometer which would make it more sensitive:

Answer 16

narrower tube

bigger bulb

Question 17

Define the specific latent heat of fusion:

Answer 17

the energy needed per kg to cause a substance to change state without a rise in temperature
melting point

Question 18

Define the specific latent heat of vaporization:

Answer 18

the energy needed per kg to cause a substance to change state without a rise in temperature
boiling point

Question 19

Define specific heat capacity:

Answer 19

the energy required per kg per degree Celsius to raise the temperature of a substance

Question 20

What does melting point depend on?

Answer 20

the force strength of a solid

Question 21

What does boiling point depend on?

Answer 21

the atmospheric pressure

Question 22

Energy required =

Answer 22

mass * specific heat capacity * change in temperature

Question 23

Explain in terms of molecules what conduction is:

Answer 23

the transfer of thermal energy from a hot end to a cold end (caused by difference in temp)
molecules at heated end vibrate more as they gain energy
the molecules transfer energy to one another as they collide
in metals free electrons come lose and transfer thermal energy faster through collisions

Question 24

Explain in terms of molecules what convection is:

Answer 24

caused by a difference in densities
process by which thermal energy transfers from one place to another by fluid motion
the hot molecules are more dense so they rise and the cold molecules are less dense so they sink
the convection currents then heat up all the molecules

Question 25

Define what radiation is:

Answer 25

Invisible radiation rays transferred by electromagnetic waves which doesn’t require a medium to travel in
rays from sun heat up the earth