IGCSE物理热学知识点总结 定义公式拿A缺一不可

之前我们也给大家介绍了CIE考试局取消了英国的IGCSE考试，但是疫情稳定的国家考试还是会正常举行的。今天我们也给大家总结了一些有关IGCSE物理热学知识点，如果有需要的同学一起来看看吧！

IGCSE物理热学知识点

Three state of matter

Melting point and boiling point

melting point

A pure substance changes from solid to liquid at a fixed temperature.

boiling point

A pure substance changes from liquid to gas at a fiexed temperature.

The kinetic model of matter

The kinetic model

Brownian motion

Brownian motion is the random motion of particles suspended in a fluid (a liquid or a gas) resulting from their collision with the quick atoms or molecules in the gas or liquid.

Evaporation

The process that water has become water vapour in the air.

Why does evaporation make things cooler?

Th e particles that are escaping from the water are the fastest-moving ones. They are the particles with the most energy.

This means that the particles that remain are those with less energy, and so the water is colder.

Force and kinetic theory

Attractive force

It is the attractive force that hold together the particles that made up matter.

Attractive force in solid,liquid and gas

force in solid > force in liquid > force in gas

Kinetic theory and changes of state

Heat the material  and eventually the particles have sufficient energy for all of the attractive forces between particles to be overcome. Thus, the state of matter is changed.

Gases and kinetic theory

Gas exerts a pressure

High-speed molecules collide with the wall of container.

Each collision thus results in a change of momentum of the air molecule.

Each molecule that collides with the wall exerts a tiny force.

Because there are so many fast-moving particles, and because they collide so frequently with all the surfaces in the room, they exert a large force.

Boyle's law

The volume of a fi xed mass of gas is inversely proportional to its pressure, provided its temperature remains constant.

Formula

Temperature and pressure

For fixed volume of gas, when the heat increases, the pressure will increase, too.

Chapter 10 Thermal properties of matter

Temperature and temperature scale

Internal energy

Internal energy is the total energy of all of the particles.

temperature

Temperature is a measure of the average kinetic energy of the individual particles.

Two fixed points

 - the freezing point of pure water at atmospheric pressure,

 - the boiling point of pure water at atmospheric pressure.

Designing a thermometer

Linear scale

The marks on the scale are evenly spaced.

Range

The difference between highest fixed point to lowest fixed point.

Sensitivity

The degree to measure the small change of temperature.

Responsiveness

The time for liquid to reach the temperature of the surroundings.

Using thermocouple

To use the thermocouple, its ends are connected to a sensitive voltmeter.

Then one junction is placed in melting ice at 0 °C while the other is placed in the object whose temperature is to be measured.

The voltmeter shows a reading.

Advantages for thermocouple

Thermocouples can be used to measure high temperatures.

Thermocouples are useful for measuring rapidly varying temperatures.

Thermocouples can be linked to other electrical circuits or a computer.

Thermal expansion

Thermal expansion

Most substances (solids, liquids and gases) expand when they are heated.

Thermal expansion in solid, liquid and gas

Thermal capacity

Thermal capacity is a measurable physical quantity equal to the ratio of the heat added to (or removed from) an object to the resulting temperature change.

Formula

thermal capacity and materials

Metal objects heat up easily – their thermal capacities are low.

Objects made of non-metals and liquids (such as water and oil) have higher thermal capacities.

Specific heat capacity

The energy required per kilogram and per degree Celsius to raise the temperature of a substance.

Formula

Latent heat

The energy is supplied to melt or boil a substance without raising its temperature.

Formula

specific latent heat of vaporisation

The energy per kilogram required to cause a substance to change state from liquid to gas at its boiling point.

specific latent heat of fusion

The energy per kilogram required to cause a substance to change state from solid to liquid at its melting point.

Thermal energy transfer

conduction

Thermal energy (heat) is transferred from the hot end to the cold end as the faster particles pass on their extra motion to particles all along the bar.

The process is called conduction.

Conductor

Materials that are good at conducting heat.

insulator

Materials that are not good at conducting heat.

Metals are good conductors

In a metal there are particles called electrons that can move about freely. Electrons carry energy when an electric current fl ows through a metal.

convection

Convective heat transfer occur between two objects separated by a moving interface of liquid or gas.

convection current

A convection current is a movement of a fl uid that carries energy from a warmer place to a cooler one.

Thermal radiation

Thernal radiaion can travel through a vacuum.

Radiation rate

All objects give out some thermal radiation.

The higher their surface temperature and the greater their surface area, the more energy they radiate per second.

emmiter and absorber

Matt black surfaces are the best absorbers and absorbers as well.

reflector

Shiny or white surfaces are the best refl ectors.

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