5th grade Light and HEAT. (AGV)

     LIGHT  and HEAT.

After learning about different types of energy, we are going to focus on one of them. LIGHT




What is light?
Light is a form of energy that we can see directly with our eyes. It is formed by  Photons. Photons are the smallest particle of light.

Sources

Light can come from natural sources: sun and lightning

from artificial or man-made source: bulbs or candles.

Properties of light

-Speed: light travels very fast 300 million m/sec. Light is the fastest form of energy.

-Colour: it looks white but it is made up of seven colors, the same as the rainbow: red, orange, yellow, green, light blue, indigo and violet.

We can see this when light passes through a prism. Newton found this out. Who was Isaac Newton?

ISAAC NEWTON

Was an astronomer, mathematician, inventor, philosopher and physicist from the 17th century. (Gravity) He also investigated the properties of light, by showing a white light through a prism, demonstrating that white light refracts into seven separate colors. He built the first reflecting telescope with different lenses.

When light hits an opaque object, some colors are absorbed and others are reflected.

Tomato is red because it reflects  the color red and absorbs all the other colors.

Snow is white because it reflects all the colors.

Coal is black because it absorbs all the colors and doesn’t reflect any of them.

-Direction: light travels in a straight line. When it hits an object, depending on its surface, it can:
Be absorbed

Be reflected

Be refracted

REFLECTION: light hits an object and bounces back.

If the surface is smooth, the rays reflect in the same direction.
If the surface is rough, the rays reflect in different directions.
Examples: lake surface, window or a mirror.

REFRACTION: light changes direction as it passes from one substance to another. This substance through
which light travels is called a medium.

Light can be made:

- as a chemical reaction: candle- its wax combines with oxygen to keep the flame alight.

- as an electrical circuit: made of a bulb, a switch and a battery.

Light going through different materials

-Transparent materials: allow light to pass through them.

We can see clearly. GLASS

-Translucent materials: allow some light to pass through them.

We can partly see through. SUNGLASSES

-Opaque materials: do not allow any light to pass through them. We cannot

see through. WOOD

LENSES: are pieces of curved glass or plastic that refract light. They are used in glasses,

microscopes, telescopes, cameras….

They can make objects look bigger or smaller depending on the shape of the lens.

HEAT: the flow of thermal energy is called heat. The thermal energy flows from

a warm substance to a cooler substance.

Temperature is not the same as heat. It is how hot or cold things are. We use a

thermometer to measure temperature with two scales: Celsius and Fahrenheit.

-Thermal insulators: don’t transfer heat: wool, wood, and plastic gloves.

-Thermal conductors: transfer heat quickly: metals.

Substance changes state when we add thermal energy to a substance.

-Melting: thermal energy in a solid increases, becoming liquid.
-Evaporation: thermal energy in a liquid increases, becoming gas.
-Expansion: thermal energy increases and its volume increases too.

Sunlight and health. Precautions.

Some sunlight is good for the body but too much can cause serious health problems. The ultraviolet rays

(UVA and UVB rays) can cause the skin to wrinkle and skin cancer, sunburn, cataracts,... So it

is important to protect us from the sun with sunscreen, hat and stay indoors from 12-5, and drink water

to hydrate our body.