thermal physics + extra

common (not si) unit for temperature

°C

si unit for temperature

K (kelvin)

si unit of energy transferred/work done

J (joules)

si unit of mass

kg (kilograms)

si unit of density

kg/m³

si unit of length

m (metre)

si unit of area

m²

si unit of volume

m³

si unit of speed/velocity

m/s

si unit of acceleration

m/s²

si unit of force

N (newtons)

si unit of pressure

Pa (equivalent to N/m²)

si unit for specific heat capacity

J/kg°C

explain why heating a system will change the energy stored within the system and raise its temperature or produce changes of state

• heating a system involves transferring energy to the particles of molecules within the system

• this increases the kinetic energy of the particles which means the internal energy of the system increases, which increases the temperature

• this can also produce a change of state if the energy the molecules together as opposed to increasing the kinetic energy supplied is used to overcome the bonds between them so the motion and arrangement of particles changes

  • this does not increase the temp. because no energy goes towards increasing the kinetic energy of the system

label the points on this cooling graph (the points are the same on a heating graph except they are reversed in order)

what is it called when a solid heats up into a liquid

melting

what is it called when a solid heats up into a gas

subliming/sublimation

what is it called when a liquid heats up into a gas

boiling/evaporating

what is it called when a gas cools down into a liquid

condensation

what is it called when a liquid cools down into a solid

freezing

is this substance a solid, liquid or gas and how can you tell by its arrangement and presumed motion

solid:

• molecules close together in a fixed regular lattice pattern

• strong intermolecular forces of attraction

• molecules vibrate but can’t move about

is this substance a solid, liquid or gas and how can you tell by its arrangement and presumed motion

liquid:

• molecules close together in random arrangement

• weaker intermolecular forces than solids

• molecules move around each other

is this substance a solid, liquid or gas and how can you tell by its arrangement and presumed motion

gas:

• particles far apart in random arrangement

• negligible/very weak intermolecular forces

• particles are constantly moving with random motion

describe an experiment to show constant temperature during a change of state

• fill a beaker with boiling water

• put ice in the beaker and record the temperature of the ice every 10s as it melts

• the results should be a straight line on a temperature/time graph as the energy in the ice goes towards breaking the bonds in the ice rather than increasing its kinetic energy

how is specific heat capacity defined and what is its si unit

specific heat capacity is the amount of energy required to increase the temperature of 1kg of a substance by 1°C

• it is measured in J/kg°C

what is the equation for change in thermal energy

ΔQ = m × c × ΔT

Change in thermal energy [J] = Mass [kg] x Specific heat capacity [J/kg 0C] x Change in temperature [0C]

5.14) describe an experiment to investigate the specific heat capacity of materials including water and some solids

• measure the mass of an insulating container, fill it with 200ml water and then measure the mass again (the difference between these numbers is the mass of the water)

• measure the temperature of water and turn on power which is connected to the water by a immersion heater and connect it to voltmeter and ammeter

• wait 1 minute and then measure the water temperature and take voltmeter and ammeter measurements

• calculate energy supplied using equation: energy supplied = voltage x current x time

• substitute the answer as Q in the equation Q=mcΔT to find specific heat capacity

• repeat 3 times to find an average

• plot graph

5.7) which changes occur to evaporate/ boil a liquid into a gas

• liquids have some kinetic energy

• as they are heated, particles vibrate more so their kinetic energy increases

• kinetic energy increases → particles vibrate more → frequency of collisions increases → particles get further away from eachother

• liquid reaches boiling point when particles are far away enough that their intermolecular forces break and they become gases

5.7) which changes occur to melt a solid into a liquid

• solids can’t move so they have no net kinetic energy

• as they are heated, the particles vibrate so kinetic energy is gained

• kinetic energy increases → particles vibrate more → frequency of collisions increases → particles get further away from eachother and become liquid because they break free of their previous bonds

how do molecules in a gas exert a pressure on the walls of a container

• gas molecules have rapid and random motion

• when they hit the walls of the container, they exert a force

• pressure = force/area and the force exerted from the gas molecules is spread out over the area of the container’s walls

why is 0K absolute zero

• at absolute zero the particles have no thermal energy or kinetic energy, so they stop moving

• this temperature is called 0K, which is equivalent to -273°C

how to convert between Kelvin and Celsius scales

• C = K - 273

• K = C + 273

K is always bigger than C

why does an increase in temperature result in an increase in the average speed of gas molecules

as you increase the temperature of a gas

• the kinetic energy of the gas particles increases proportionally to temperature

• so particles move around with a greater average velocity/speed

what is the relationship between the Kelvin temperature of a gas and the average kinetic energy of its molecules

kelvin temperature is directly proportional to the average kinetic energy of its molecules

explain the relationship between Kelvin temperature and pressure at constant volume (pressure law)

• as a gas is heated, kinetic energy of the particles increases so their average speeds increase

• this means there are more collisions per second with the wall, so they exert a greater average force on the wall

• this means that the total pressure exerted by the particles increases:

  • pressure is force / area, and the force here increases while the area stays the same

• therefore the relationship between pressure and temperature is directly proportional (as pressure increases, temperature increases and vice versa)

  • this assumes volume + mass are constant

explain the relationship between pressure and volume at constant temperature (boyle’s law)

• if temperature is constant, average particle speed is constant

• as volume decreases in a container, particle collision frequency per second increases

  • this is because the same amount of particles are moving around in a smaller volume so they are more likely to hit the sides

• more collisions exerted per second on the sides means that the particles exert a greater force on the wall over a given time, so the average force exerted on the walls increases

• this means that the total pressure exerted by the particles increases:

  • pressure is force / area, and the force here increases while the area stays the same

• this means that the relationship between pressure and volume is inversely proportional: as volume decreases, pressure increases and vice versa

  • assumes constant temperature + mass

equation for the relationship between the pressure and Kelvin temperature of a fixed mass of gas at constant volume

P₁/T₁ = P₂/T₂

temperature must always be in kelvin

• P₁ = (P₂*T₁)/T₂

• P₂ = (P₁*T₂)/T₁

• T₁ = (T₂*P₁)/P₂

• P₂ = (P₁*T₂)/T₁

  • if youre arranging for P₁, you need to divide by the opposite letter and the opposite number so you need to divide by T₂. then put the other values (P₂*T₁) over the T₂

equation for the relationship between the pressure and volume of a fixed mass of gas at constant temperature

P₁V₁ = P₂V₂

• if youre arranging for P₁, put the value with the same number but the opposite letter underneath the dividing sign (so you put T₁ under the division sign), and then multiply the other numbers over the division sign

  • so you get (T₂ * P₂)/V₁

5.3) equation for density

density (kg/m³)= mass (kg) / volume (m³)

5.4) how can you find the density of a regular or irregular object

regular objects

• measure the sides of the object using a ruler

• calculate the volume

• do mass/volume to find the density

irregular objects

• submerge in eureka can and measure the volume of water displaced

• do mass/volume to find the density

5.5) equation for pressure

pressure (Pa or N/m²)= force (N) / area (m²)

5.6) describe how pressure moves in fluids at rest

pressure moves equally in all directions

explain why heating a system will change the energy stored within the system and raise its temperature or produce changes of state

• heating a system involves transferring energy to the particles of molecules within the system

• this increases the kinetic energy of the particles which means the internal energy of the system increases, which increases the temperature

• this can also produce a change of state if the energy the molecules together as opposed to increasing the kinetic energy supplied is used to overcome the bonds between them so the motion and arrangement of particles changes

  • this does not increase the temp. because no energy goes towards increasing the kinetic energy of the system

label the points on this cooling graph (the points are the same on a heating graph except they are reversed in order)

what is it called when a solid heats up into a liquid

melting

what is it called when a solid heats up into a gas

subliming/sublimation

what is it called when a liquid heats up into a gas

boiling/evaporating

what is it called when a gas cools down into a liquid

condensation

what is it called when a liquid cools down into a solid

freezing

is this substance a solid, liquid or gas and how can you tell by its arrangement and presumed motion

solid:

• molecules close together in a fixed regular lattice pattern

• strong intermolecular forces of attraction

• molecules vibrate but can’t move about

is this substance a solid, liquid or gas and how can you tell by its arrangement and presumed motion

liquid:

• molecules close together in random arrangement

• weaker intermolecular forces than solids

• molecules move around each other

is this substance a solid, liquid or gas and how can you tell by its arrangement and presumed motion

gas:

• particles far apart in random arrangement

• negligible/very weak intermolecular forces

• particles are constantly moving with random motion

describe an experiment to show constant temperature during a change of state

• fill a beaker with boiling water

• put ice in the beaker and record the temperature of the ice every 10s as it melts

• the results should be a straight line on a temperature/time graph as the energy in the ice goes towards breaking the bonds in the ice rather than increasing its kinetic energy

how is specific heat capacity defined and what is its si unit

specific heat capacity is the amount of energy required to increase the temperature of 1kg of a substance by 1°C

• it is measured in J/kg°C

what is the equation for change in thermal energy

ΔQ = m × c × ΔT

Change in thermal energy [J] = Mass [kg] x Specific heat capacity [J/kg 0C] x Change in temperature [0C]

5.14) describe an experiment to investigate the specific heat capacity of materials including water and some solids

• measure the mass of an insulating container, fill it with 200ml water and then measure the mass again (the difference between these numbers is the mass of the water)

• measure the temperature of water and turn on power which is connected to the water by a immersion heater and connect it to voltmeter and ammeter

• wait 1 minute and then measure the water temperature and take voltmeter and ammeter measurements

• calculate energy supplied using equation: energy supplied = voltage x current x time

• substitute the answer as Q in the equation Q=mcΔT to find specific heat capacity

• repeat 3 times to find an average

• plot graph

5.7) which changes occur to evaporate/ boil a liquid into a gas

• liquids have some kinetic energy

• as they are heated, particles vibrate more so their kinetic energy increases

• kinetic energy increases → particles vibrate more → frequency of collisions increases → particles get further away from eachother

• liquid reaches boiling point when particles are far away enough that their intermolecular forces break and they become gases

5.7) which changes occur to melt a solid into a liquid

• solids can’t move so they have no net kinetic energy

• as they are heated, the particles vibrate so kinetic energy is gained

• kinetic energy increases → particles vibrate more → frequency of collisions increases → particles get further away from eachother and become liquid because they break free of their previous bonds

how does conduction work in non-metal solids or liquids (insulators)

• solid is heated up

• the heat energises the molecules so vibration (kinetic energy) increases

• the vibration (high kinetic energy) slowly moves throughout the solid because as the molecules vibrate more they hit adjacent molecules, making them vibrate more too and increasing their kinetic energy

• this transfers heat energy from hotter to cooler parts of the non-metal

how does conduction work in metals and how does it compare to that of insulator solids or liquids

• some electrons in a metal can leave their atoms and move around the atom as a free (delocalised) electron, leaving metal ions behind

  • metals are already good conductors

• this means when the free electrons absorb heat energy, they move much faster so they are more likely to crash into metal ions

• some of the kinetic energy is absorbed by the ions so they vibrate faster and with greater amplitude, transferring heat energy from hotter to colder parts of the metal

• this is faster than conduction in non-metals/insulators, where conduction is caused by vibrations passed between atoms because they dont have free electrons

what is conduction

the transferral of thermal energy in solids or liquids by the vibration of particles

how do convection currents work in fluids

• energy is transferred from heat source to air

• particles move further apart so the fluid expands

• it then rises up because it’s less dense

• as it rises, it cools because it transfers heat to its surroundings so it becomes less dense and sinks

• cooler air becomes denser and sinks

  • the corners of a beaker or room which aren’t affected by the heating can push the fluid around

• this process repeats

how does radiation happen and where can it happen

• all bodies emit infrared radiation

• the hotter an object, the more infrared radiation it radiates in a given time

• radiation can operate in a vacuum because it doesn’t require particles to transfer energy

rank the absorbing and emitting abilities of thermal radiation of:

shiny, dull/dark, black, white surfaces

from best to worst

black

• best emitter/absorber

• thermal energy is radiated,

  dull/dark, white, shiny

• (shiny surfaces reflect light, not absorb it)

• worst emitter/absorber

• thermal energy is reflected

what are some examples of convection in everyday phenomena

• radiators

• fridges

• weather

• air conditioning (uses reverse convection currents, i.e cooling current)

why does convection work only in fluids

in gases and liquids the particles can move past each other but in solids they can’t

how can you stop unwanted convection (currents)

stop the free flow of fluids by containing/reducing area of the convection current

• for example, wearing a blanket reduces air movement, so it reduces the convection current

describe an experiment to investigate conduction

1. use a clamp and stand to secure a conduction ring over a bunsen burner

2. attach ball bearings to the ends of the metal strips using wax

3. turn the strips upside down and heat the centre so each of the strips is heated at the central point where they meet

4. when heat is conducted along to the ball bearing the wax melts and the ball bearing drops

5. time how long this takes for the strips and record in a table

6. repeat and find an average

• independent var: type of metal

• dependent var: rate of conduction

• control var: size and thickness of metal strips

describe an experiment to investigate convection

1. fill a beaker with cold water and put it on top of a tripod and heatproof mat

2. pick up the potassium permanganate crystals and drop them into the centre of the beaker

3. heat the beaker with a bunsen burner and record observations

4. repeat experiment with hot water and record observations

   • convection currents will be formed in both beakers but the current is faster in hot water

• independent var: temp of water

• dependent var: rate of convection

• control vars: Amount of water in beaker, Size of bunsen burner flame, Size of potassium permanganate crystal

describe an experiment to investigate radiation (6)

1. make sure theres an equal volume of water in each bottle

2. place both bottles an equal distance away from an infrared heater

3. the bottles should have the same heater output

4. make sure the starting temperature of the water is the same

5. measure the temperature of water in the bottles after a given time

6. repeat the investigation more than once

7. calculate a mean

8. take care to avoid burns from heater/clean up water spillages

how do molecules in a gas exert a pressure on the walls of a container

• gas molecules have rapid and random motion

• when they hit the walls of the container, they exert a force

• pressure = force/area and the force exerted from the gas molecules is spread out over the area of the container’s walls

why is 0K absolute zero

• at absolute zero the particles have no thermal energy or kinetic energy, so they stop moving

• this temperature is called 0K, which is equivalent to -273°C

how to convert between Kelvin and Celsius scales

• C = K - 273

• K = C + 273

K is always bigger than C

why does an increase in temperature result in an increase in the average speed of gas molecules

as you increase the temperature of a gas

• the kinetic energy of the gas particles increases proportionally to temperature

• so particles move around with a greater average velocity/speed

what is the relationship between the Kelvin temperature of a gas and the average kinetic energy of its molecules

kelvin temperature is directly proportional to the average kinetic energy of its molecules

explain the relationship between Kelvin temperature and pressure at constant volume (pressure law)

• as a gas is heated, kinetic energy of the particles increases so their average speeds increase

• this means there are more collisions per second with the wall, so they exert a greater average force on the wall

• this means that the total pressure exerted by the particles increases:

  • pressure is force / area, and the force here increases while the area stays the same

• therefore the relationship between pressure and temperature is directly proportional (as pressure increases, temperature increases and vice versa)

  • this assumes volume + mass are constant

explain the relationship between pressure and volume at constant temperature (boyle’s law)

• if temperature is constant, average particle speed is constant

• as volume decreases in a container, particle collision frequency per second increases

  • this is because the same amount of particles are moving around in a smaller volume so they are more likely to hit the sides

• more collisions exerted per second on the sides means that the particles exert a greater force on the wall over a given time, so the average force exerted on the walls increases

• this means that the total pressure exerted by the particles increases:

  • pressure is force / area, and the force here increases while the area stays the same

• this means that the relationship between pressure and volume is inversely proportional: as volume decreases, pressure increases and vice versa

  • assumes constant temperature + mass

equation for the relationship between the pressure and Kelvin temperature of a fixed mass of gas at constant volume

P₁/T₁ = P₂/T₂

temperature must always be in kelvin

• P₁ = (P₂*T₁)/T₂

• P₂ = (P₁*T₂)/T₁

• T₁ = (T₂*P₁)/P₂

• P₂ = (P₁*T₂)/T₁

  • if youre arranging for P₁, you need to divide by the opposite letter and the opposite number so you need to divide by T₂. then put the other values (P₂*T₁) over the T₂

equation for the relationship between the pressure and volume of a fixed mass of gas at constant temperature

P₁V₁ = P₂V₂

• if youre arranging for P₁, put the value with the same number but the opposite letter underneath the dividing sign (so you put T₁ under the division sign), and then multiply the other numbers over the division sign

  • so you get (T₂ * P₂)/V₁

how does conduction work in non-metal solids or liquids (insulators)

• solid is heated up

• the heat energises the molecules so vibration (kinetic energy) increases

• the vibration (high kinetic energy) slowly moves throughout the solid because as the molecules vibrate more they hit adjacent molecules, making them vibrate more too and increasing their kinetic energy

• this transfers heat energy from hotter to cooler parts of the non-metal

how does conduction work in metals and how does it compare to that of insulator solids or liquids

• some electrons in a metal can leave their atoms and move around the atom as a free (delocalised) electron, leaving metal ions behind

  • metals are already good conductors

• this means when the free electrons absorb heat energy, they move much faster so they are more likely to crash into metal ions

• some of the kinetic energy is absorbed by the ions so they vibrate faster and with greater amplitude, transferring heat energy from hotter to colder parts of the metal

• this is faster than conduction in non-metals/insulators, where conduction is caused by vibrations passed between atoms because they dont have free electrons

what is conduction

the transferral of thermal energy in solids or liquids by the vibration of particles

how do convection currents work in fluids

• energy is transferred from heat source to air

• particles move further apart so the fluid expands

• it then rises up because it’s less dense

• as it rises, it cools because it transfers heat to its surroundings so it becomes less dense and sinks

• cooler air becomes denser and sinks

  • the corners of a beaker or room which aren’t affected by the heating can push the fluid around

• this process repeats

how does radiation happen and where can it happen

• all bodies emit infrared radiation

• the hotter an object, the more infrared radiation it radiates in a given time

• radiation can operate in a vacuum because it doesn’t require particles to transfer energy

rank the absorbing and emitting abilities of thermal radiation of:

shiny, dull/dark, black, white surfaces

from best to worst

black

• best emitter/absorber

• thermal energy is radiated,

  dull/dark, white, shiny

• (shiny surfaces reflect light, not absorb it)

• worst emitter/absorber

• thermal energy is reflected

what are some examples of convection in everyday phenomena

• radiators

• fridges

• weather

• air conditioning (uses reverse convection currents, i.e cooling current)

why does convection work only in fluids

in gases and liquids the particles can move past each other but in solids they can’t

how can you stop unwanted convection (currents)

stop the free flow of fluids by containing/reducing area of the convection current

• for example, wearing a blanket reduces air movement, so it reduces the convection current

describe an experiment to investigate conduction

1. use a clamp and stand to secure a conduction ring over a bunsen burner

2. attach ball bearings to the ends of the metal strips using wax

3. turn the strips upside down and heat the centre so each of the strips is heated at the central point where they meet

4. when heat is conducted along to the ball bearing the wax melts and the ball bearing drops

5. time how long this takes for the strips and record in a table

6. repeat and find an average

• independent var: type of metal

• dependent var: rate of conduction

• control var: size and thickness of metal strips

describe an experiment to investigate convection

1. fill a beaker with cold water and put it on top of a tripod and heatproof mat

2. pick up the potassium permanganate crystals and drop them into the centre of the beaker

3. heat the beaker with a bunsen burner and record observations

4. repeat experiment with hot water and record observations

   • convection currents will be formed in both beakers but the current is faster in hot water

• independent var: temp of water

• dependent var: rate of convection

• control vars: Amount of water in beaker, Size of bunsen burner flame, Size of potassium permanganate crystal

describe an experiment to investigate radiation (6)

1. make sure theres an equal volume of water in each bottle

2. place both bottles an equal distance away from an infrared heater

3. the bottles should have the same heater output

4. make sure the starting temperature of the water is the same

5. measure the temperature of water in the bottles after a given time

6. repeat the investigation more than once

7. calculate a mean

8. take care to avoid burns from heater/clean up water spillages

what are some situations where you want to reduce energy transfer

Keeping a house warm

Keeping a hot drink hot or cold

Dressing to stay warm in cold weather

how to reduce conduction

use materials with a low thermal conductivity: insulators

how does insulation keep something warm

• The insulator contains the trapped air, which is a poor thermal conductor

• Trapping the air also prevents it from transferring energy by convection

• This reduces the rate of energy transfer from the object, meaning that it will stay warmer for longer

on a heating graph why do the two lines have different gradients

the substance is at different states here

so they have different specific heat capacities

so one has a faster rate of reaction than the other

what do you need for conduction/convection/radiation to occur

conduction: physical contact between two things

convection: fluids (particles that have net movement) and a gap between objects, i.e not next to each other

radiation: very different temperatures