# Physics - Thermal Effects

This set is for IGCSE, Physics, specifically for Thermal Effects. This topic has 8 sub-topics which are:

Moving Particles          Temperature          Heating Gases          Thermal Conduction          Convection          Thermal Radiation          Liquids and Vapours          Specific Heat Capacity

## Moving Particles

Everything is either a solid, liquid or gas:

A solid has a fixed shape and volume. The particles are held together by strong bonds. The particles vibrate but cannot change position.

A liquid has a fixed volume but no a fixed shape. The particles are close together and attract eachother. They vibrate vigorously and can chage position.

A gas has no fixed shape or volume. The particles are almost free of attraction. The particles vibrate vigorously and can change position.

All particles move in a random direction and are knocked by other particles.

If a particles is moving faster (a hotter material), the more its internal energy is.

If a hot material touches a cold one then the hotter one will become colder and the colder one will become hotter.

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## Temperature

Temperature is changed by the speed of an object. This speed can then be measured by thermometers. Temperature is usually measured in degrees celsius.

There is no temperature colder than absolute 0 which is -273 degrees celsius. This is where the particles in a object do not move at all.

In science, temperature is measured using Kelvins. This is where absolute 0 is 0 kelvins instead of -273 degrees celsius.

Kelvin was changed to degrees celsius as it made it simpler to distinguish between the temperature of the weather.

To convert degreed celsius to kelvin this equation is used:

kelvin (K) = Celcius (° C) + 273

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## Heating Gases

Pressure and temperature (K) are directly proportional to one another.

If the pressure doubles, so does the temperature (K).

(2 x pressure (kPa) ) / Kelvin (K) will always have the same value.

If the pressure changes, the new temperature can be calculated using this equation

primary pressure (kPa) / Primary Temperature (K) = secondary pressure (kPa) / secondary temperature (K)

Volume and temperature (K) are inversley protportional.

If the volume / temperature changes the new temperature / volume can be found using:

primary volume (cm³) x primary temperature (K) = secondary volume (cm³) x secondary temperature (K)

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## Thermal Conduction and Convection

Conduction is the passing of heat through a solid.

This solid has to be a conductor of electricity.

If the solid cannot conduct heat it is an insulator.

When a material is heated, particles nearest to the heat vibrate, making the particles next to it vibrate, this vibration then carries on throughout the material.

Darker coloured substances are better conductors of heat, therefore darker substances are usually hotter.

Convection is the heatig of a liquid or a gas and works in the same way a conduction.

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Radiation is the passing of heat through a vacuum.

An example is heat from the sun. The energy travels in the form of electromagnetic waves which include infrared waves. These are then absorbed which is often called thermal radiation.

As said before, darkened objects absorb heat better than shiny surfaces which reflect off the heat, which is also a form of radiation.

This has been used to our advantage in the forms of solar panels. These are black panels which turn the thermal energy into electrical energy.

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## Liquids and Vapours

Evapouration is where a liquid is heated a made into a vapour.

Boiling is a rapid form of evapouration.

Condensation is where a gas is cooled and made into a liquid.

Freezing is where a liquid is cooled, the particles slow down and the liquid is now a solid.

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## Specific Heat Capacity

The heat capacity of an object is the amount of energy put in to changing it's temperature one degree.

An experiment can be done to find the heat capacity, it is:

energy transferred (J) = mass (kg) x heat capacity (J / kg °C) x temperature change (°C) or:

E = m c ΔT

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