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Heat and light

Heat and temperature

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).

measuring tip


digital thermometers

analogue thermometers

coloured alcohol



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

Thermal energy can be transferred through space by electromagnetic waves.


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

Thermal energy travels through a gas or through a liquid.


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

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


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

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.

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.

Heat and matter

States of Matter

Heat and Matter: Changes in State



changes into a

When a solid



changes into a

When a liquid



changes into a

When a solid

Heat and Matter: Changes in State

light bulbs

require electricity


some living things

the Sun


of light


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.




light pass through

do not let any


seen clearly

objects cannot be


allow light to pass


seen clearly

objects can be


allow light to pass



Types of

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

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

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

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

Basic Laws of Light

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

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

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

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.

Basic Laws of Light

vibration as heat.

When we touch the object, we feel this

object vibrate faster.

This energy makes the molecules of the

energy is absorbed by the object.

When light energy hits an object, some of the

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

Transforming Light into Heat