Theme B - B.1 - Thermal energy transfers

Question 1

What are the properties of solids?

Answer 1

• fixed volume and do not flow
• particles are arranged in regular rows
• particles have little energy hence can only vibrate around fixed positions
• Strong intermolecular forces

Question 2

What happens when solids are heated?

Answer 2

• Particles gain energy-> Move further apart-> weakens intermolecular forces(thermal expansion)
• Solids expand less as comapred to liquids and gases

Question 3

What are the properties of liquids?

Answer 3

• flow and take the shape of the container
• fixed volume
• random particle arrangement
• intermolecular forces are weaker than solids but stronger than gas
• More expansion than solids but less expansion than gases

Question 4

What are the properties of gases?

Answer 4

• flow and take the shape of the container
• volume changes based on pressure and temperature
• particles are far and arranged randomly
• high energy and random movement
• gases expand the most

Question 5

What is internal energy?

Answer 5

Sum of potential energy and kinetic energy. Changing either of these can change internal energy.

Question 6

Which state of matter has the highest internal energy?

Answer 6

Gases.

Question 7

What is density defined as?

Answer 7

Mass per unit volume.

Question 8

What is the relationship between temperature and pressure?

Answer 8

if temperature decreases, pressure decreases and if temperature increases, pressure increases

Question 9

What is absolute zero?

Answer 9

The lowest temperature possible where the pressure and volume of a substance is equal to zero and the particles have zero kinetic energy.

Question 10

What is the absolute temperature?

Answer 10

The temperature on the kelvin scale.

Question 11

What is the relationship between kinetic energy and temperature?

Answer 11

As kinetic energy increases, the temperature increases.

Question 12

What is the formula for average kinetic energy of molecules?

Answer 12

E=(3/2)KT where E is the average kinetic energy of the molecules, K is the boltzman constant and T is the absolute temperature.

Question 13

What is specific heat capacity?

Answer 13

The amount of energy required to increase the temperature of 1kg of a substance by 1K. Or: the heat released by a substance when its temperature decreases by 1K.

Question 14

What is phase change?

Answer 14

When a substances changes from one phase to the other(e.g solid->liquid)

Question 15

During a phase change, all energy supplied is transferred to the _ energy of the particles and not _ energy.

Answer 15

potential, kinetic

Question 16

During phase change, the temperature of the substance _ _.

Answer 16

remains constant

Question 17

What is the specific latent heat of a substance?

Answer 17

The amount of energy required to change the phase of 1kg of a substance at constant temperature. For solid->liquid it is the specific latent heat of fusion. For liquid->gas it is the specific latent heat of vaporisation.

Question 18

What is the formula for latent heat?

Answer 18

Q = ml where Q is thermal energy, m is latent heat and l is latent heat.

Question 19

When does a thermal energy transfer occur?

Answer 19

When there is a difference in temeperature between two bodies.

Question 20

How does thermal energy transfer?

Answer 20

From an area of higher temeperature to an area of lower temperature until thermal equilibrium is reached.

Question 21

What is conduction?

Answer 21

The transfer of thermal energy between particles in direct contact.

Question 22

In which state of matter does conduction occur best in?

Answer 22

Solids, as the particles are really close to each other.

Question 23

Describe the process of thermal energy transfer in solids.

Answer 23

Thermal energy is supplied to one part of the solid and gets converted into kinetic energy and the particles vibrate more. Kinetic energy is transferred to neighboring particles through collision. When thermal equilibrium is reached net transfer is zero.

Question 24

Why are metals the best conductors?

Answer 24

They have a sea of delocalised electrons which transfer the heat throughout the metal.

Question 25

Good thermal transferrers are called _ while poor thermal transferrers are called _.

Answer 25

conductors, insulators

Question 26

The rate at which thermal energy is transferred is the amount of _ _ per unit time.

Answer 26

energy transferred

Question 27

What does fouriers conduction law state?

Answer 27

The rate at which thermal energy is transferred depends on the thermal conductivity of the material, cross sectional area and difference in temperature between the two parts.

Question 28

What is the formula for fouriers law of conduction?

Answer 28

(ΔQ∕Δt)=-kA(Δt/Δx)

Question 29

What is convection?

Answer 29

Transfer of thermal energy due to the mass movement of molecules caused by a difference in density. It best occurs in liquids and gasses.

Question 30

Describe the process of convection.

Answer 30

1. Thermal energy is transferred to one part of the fluid
2. This energy is converted to kinetic energy for the particles closests to the heat source
3. They collide with neighboring particles so the particles spread further apart
4. The particle is now lense dense so it rises
5. Process repeats

Question 31

What is thermal radiation?

Answer 31

Transfer of energy by electromagnetic waves. The properties of a material affect how good it is at absorbing, emitting and reflecting thermal radiation.

Question 32

Dark coloured surfaces are _ absorbers, _ emitters and _ reflectors

Answer 32

good, good, poor

Question 33

Light surface are _ absorbers, _ emitters and _ reflectors

Answer 33

poor,poor,good

Question 34

What is intensity?

Answer 34

The amount of power incident on one square meter of the surface of an object.

Question 35

What is the formula for intensity?

Answer 35

I=P/A

Question 36

Intensity is inversely proportional to the _ _ between the _ and the _ on which its energy is incident.

Answer 36

Inversely proportional

Question 37

What is a black body?

Answer 37

An object that absorbs all the energy of all wavelengths of the electromagnetic spectrum that are incident upon it.

Question 38

Peak intensity is dependant on the _ of the black body.

Answer 38

Temperature

Question 39

As temeperature changes

Answer 39

1. Peak intensity is lower
2. Overall intensity is lower
3. Area below the curve decreases so the total power emitted is less
4. Peak intensity occurs at a longer wavelength

Question 40

What does Wien’s law state?

Answer 40

The wavelength at which maximum intensity of radiation is emitted is related to the absolute temperature.

Question 41

What is the formula for Wien’s law?

Answer 41

λT=2.9 x 10^-3

Question 42

What is luminosity?

Answer 42

The amount of energy emitted per second by a black body.

Question 43

What is the stefan-boltzman law?

Answer 43

Luminosity is directly proportional to the area of the star and also directly proportional to its absolute temperature.

Question 44

What is the formula for the stefan boltzman law?

Answer 44

L=σAT^4

Question 45

What is apparent brightness?

Answer 45

A measure of how bright a star appears. It is measured by the amount of energy received per square meter per second by an observer on earth. Also known as apparent magnitude. Or the amount of power per square meter.

Question 46

What does apparent brightness depend on?

Answer 46

The luminosity of the star and the distance.