Thermal physics

Temperature

A measure of the average(not impacted by size and mass) random kinetic energy of the particles of a substance.

Si unit is Kelvin “°K” and Degree Celsius.

Equation: Kinetic energy is given by E = ½ mv² 

Heat

Energy transfer process due to a temperature difference.

The Si unit is Joules(J) and it is represented by the letter “Q” in equations.

Thermal energy

the total energy of a substance due to the movement of particles.

What happens when a warm cup of coffee poors its content on an iceburg?

Because heat energy always flows from an area/system of high KE to one with lower KE, the molecules in the coffee that are moving faster(due to their temperature) in comparison to the iceberg so when they bombard the slower moving molecules of the ice burg their energy will transfer until a point of equilibrium where the temperature of the two are balanced. In this case, the whole mass of the iceburg will not be wamred by this energy transfer form a single cup of coffee because of the extreme mass and area difference

Internal energy

The total energy stored by the particles making up a substance/system. (KE and potential energy)

Heat energy and thermal energy

Heat Energy is the flow of thermal energy between two objects of different temperature whereas the thermal energy tells about how much is the transfer of energy due to temperature difference between two bodies.

Similarity between temperature and heat

Heat is a transfer of thermal energy caused by a difference in temperature between molecules, referring to intensity of heat.

How heat transfer works

Heat is a type of energy transferred from objects at “high” temperatures to objects at “low” temperatures. Objects don’t contain heat, they contain internal energy. When objects have different temperatures touch each other, the object with more energetic particles will transfer energy to the other with less energetic particles.

Conduction

Thermal conduction is the transfer of heat (internal energy) by collisions of particles and movement of electrons within a substance through direct contact

Convection realtionship

More heat, faster current.

SHC examples

The specific heat of water is 4.18 J/g°C. This means that it takes 4.18 joules of energy to raise the temperature of 1 gram of water by 1 degree Celsius. So the high specific heat capacity of water, eg. allows it to absorb and store a large amount of heat energy from the sun, which in turn helps to regulate the Earth's temperature and climate. It also plays a crucial role in the cooling systems of many industrial processes, as well as in heating and cooling systems used in homes and buildings.

SHC examples

The specific heat of copper is 0.39 J/g°C. This means that it takes less energy to raise the temperature of copper than water. This makes copper a good conductor of heat, which is why it is often used in cookware and heating elements.

What happens when you heat up a substance

the particles gain energy in their kinetic energy store and this increases the substance’s internal energy. Thus increasing it’s temperature.

Why do the substances not change temperature when changing state?

Since the energy we are providing is being used to weaken or break the intermolecular bonds holding the particles together instead of increasing the particle’s internal energy, the overall temperature won’t change in these regions until all of the substance has changed state.

What about for reverse, when cooling a substance?

The state changes involve the formation of new bonds between particles which releases energy(counteracting the cooling), so this is what keeps the temperature constant during the state change.

What is latent heat?

The amount of energy required to change the state of a material without changing its temperature. It depends on the type of substance(as different materials have different strengths of the bonds holding the particles together) and the amount of it.

What is the Specific Latent Heat?

The energy required to change 1kg of a particular substance from one state to another, without changing the temperature.

What factors affect heat transfer

the temperature difference, the mass of the substance, and the type ofsubstance and phase of the substance.

What is SLH of fusion?

The amount of energy needed to melt or freeze the material at its melting point.

What is SLH of Vaporisation?

The amount of energy needed to boil or condense the material at its boiling point.

Q= m x L

Q is energy (J) required/released, M is mass(kg) and L is specific Latent Heat(J/kg).

Conduction

When vibrating particles transfer energy to neighbouring particles(direct physical contact) and occurs mainly in solids since the particles are very packed so there are lots of particles colliding.'

Energy is transferred between particles

Convection

It occurs mainly in fluids, since the particles aren’t fixed thus when they gain KE they all move faster causing the more “energetic particles” to move away from the warmer regions towards the colder, spreading the high-energy particles out.

• the warmer region of the fluid expands, becoming less dense than the cooler.

• The temperature difference within the fluid can create a current.

• Warm up(rises), cold down(sinks).

Particles themselves move.

Radiation

Heat transferred by infrared radiation, which is a type of electromagnetic radiation that involves waves and no particles since it transmits and converts the heat instead.

• All objects constantly absorb and emit radiation at the same time.

• Energy is carried by waves

Absorbers

Materials that efficiently absorb electromagnetic radiation

• dull, dark surfaces

Emitters

Materials that are efficient at radiating EM radiation are good emitters.

• Dull and dark surfaces

Give an example of a poor emitter

Rescue blankets- They prevent the evaporation of sweat by keeping the air around the skin humid. Their aluminium coating is heat-reflective(bright/shiny surfaces, and traps the natural heat your body radiates.

A solid

particles arranged in regular rows, densely packed and vibrate in their fixed position, and have strong bonds keeping the definite shape and volume.

A liquid

Atoms can move around and past eachother but are still held closely by forces of attraction, have an indefinite shape, fill up the container from the bottom and cannot be compressed.

gas

Spread out atoms that are free to travel randomly, that are lossely bonded and has an indefinite volume and shape, and fills up the whole contianer.

Alcohol/Mercury

Heat interacts with the molecules giving them KE, making them move faster, further, spreading them out taking up more space. Making the liquid expand and go up the narrow tube. So the temperature is determined by reading the level of the liquid using the temperature scale.

Colour Strip

Contains liquid crystals(heat sensitive), and when given more energy they change shape, changing their colour. The colour determines the temperature(scale/range).

Digital

Metal stem that comes into contact with the substance, metals are great conductors then allowing the thermometer to detect a temperature change.

Ear

Detects wavelengths being emitted from inside your ear and then measure the wavelengths to determine temperature.

For cooling the SLH

is the amount of energy released

Galilean

As temperature changes the density of the liquids change. Uses the concepts of boyancy and magnitude causing bubbles to sink and rise, allowing us to read temperature.

Volume

This is a measure of how much space the particles have.

Pressure

Pressure of the gas, measured in Pascals.

This is the “force per unit area” of the particles pushing on the walls of the container.