Heat and Light

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).

Thermometers

analogue thermometers

digital thermometers

screen

measuring tip

scale

coloured alcohol

Conduction

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.

Convection

Thermal energy travels through a gas or through a liquid.

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

Radiation

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 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.

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

States of Matter

Heat and Matter: Changes in State

gas.

changes into a

When a solid

liquid.

When a solid

changes into a

When a liquid

changes into a

gas.

Evaporation

Sublimation

Melting

Heat and Matter: Changes in State

Light

the Sun

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.

natural

some living things

of light

Sources

require electricity

artificial

light bulbs

Light

allow light to pass

through

Transparent

objects can be

seen clearly

allow light to pass

Types of

through

materials

Translucent

objects cannot be

seen clearly

do not let any

Opaque

light pass through

them

Basic Laws of Light

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

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

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

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

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.

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