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Heat and light

Heat is a form of energy that passes from a hotter object to a colder one. An object gets warmer when it absorbs heat and gets cooler when it gives off heat.

A source of heat is anything that produces heat:

  • Natural sources, like the Sun or lava from a volcano.
  • Artificial sources, like a heater, radiator, light bulb or wood fire.

Temperature is the measure of how hot or cold something is. We measure this using a thermometer. Thermometers can be analogue (we read the temperature on a scale) or digital (we read the temperature on a screen).

Heat and temperature



coloured alcohol

analogue thermometers

digital thermometers


measuring tip


When two objects are in contact, heat is transferred from one object to the other.

The temperature of the colder object increases, and the hotter object gets colder.


Thermal energy travels through a gas or through a liquid.

Circular movement: hotter molecules rise up, and colder molecules move down.


Thermal energy can be transferred through space by electromagnetic waves.

Example: thermal energy from the Sun is transferred to the Earth.

Heat and matter

If matter absorbs heat, its temperature increases, it gets warmer.

If matter emits heat, its temperature decreases, it cools down.

If two objects with different temperatures come into contact, heats transfers from the hotter object to the colder one and they are the same temperature.

If matter gets hot, it usually gets bigger, it expands.

If matter cools down, it usually gets smaller, it contracts.

Water is a special case: it increases in size when it freezes.

Conducting materials (conductors) let heat pass through them.

Non-conducting materials (insulators) do not let heat pass through them.

States of Matter

When a solid

changes into a



When a liquid

changes into a



When a solid

changes into a



Heat and Matter: Changes in State

Heat and Matter: Changes in State


Light is a form of energy emitted by luminous objects.

Light makes plants grow.

Light can be converted into electrical energy.

We can sense light using our sense of sight. Light enables us to see objects and distinguish shapes, sizes and colours.

Light travels in straight lines from its source.


of light


the Sun

some living things


require electricity

light bulbs

Types of



allow light to pass


objects can be

seen clearly


allow light to pass


objects cannot be

seen clearly


do not let any

light pass through



Basic Laws of Light

Reflection occurs when light energy bounces off a surface and changes direction.

The mirror reflects the light, causing it to change direction.

Light travels in a straight line from the object to the mirror.

The boy can see the reflection of the object in the mirror.

Basic Laws of Light

Refraction occurs when light passes through some transparent substances and the light energy changes direction slightly.

When we look ate the straw, it appears to be bent, because water is refracting the light.

Water changes the direction of the light energy that passes through it.

Basic Laws of Light

White light is made up of all the colours combined together. We can divide white light into colours by refraction because each coloured light travels at a specific wavelength.

Transforming Light into Heat

More light energy is absorbed by dark colours, so more light energy is transformed into heat in objects that are dark.

When light energy hits an object, some of the

energy is absorbed by the object.

This energy makes the molecules of the

object vibrate faster.

When we touch the object, we feel this

vibration as heat.