Light

Where does light come from? Our major light source: the Sun

Where else does light come from?

Sorting light sources Natural vs. Man-made (artificial)

Are these light sources? moon mirror water These items are not light sources, instead they are reflecting light from other sources.

Light travels VERY FAST – around 300,000 kilometres per second. At this speed it can go around the world 8 times in one second.

Light travels much faster than sound. For example: Thunder and lightning start at the same time, but we will see the lightning first. 2) When a starting pistol is fired we see the smoke first and then hear the bang.

We see things because they reflect light into our eyes: Homework

How does light travel? light source Light rays travel in straight lines from the light source. When it hits an opaque object, some light is absorbed and the rest reflects off. If the object is transparent, light rays pass through it easily. If the object is translucent, some light can pass through, but the rest of the light will be reflected.

The ‘angle of reflection’ is always equal to the ‘angle of incidence’. How does light reflect? on off Angle of incidence Angle of reflection The ‘angle of reflection’ is always equal to the ‘angle of incidence’.

Light can only be reflected in straight lines. off

Clear vs. Diffuse Reflection Smooth, shiny surfaces have a regular reflection: Rough, dull surfaces have a diffuse reflection. Diffuse reflection is when light is scattered in different directions

How does light form shadows? source light source Light rays travel in straight lines, radiating out from the light source. If rays are blocked by an opaque object a shadow forms where the light cannot reach. If the light source is moved closer to the object, more light is blocked and a larger shadow is formed.

Properties of Light summary Light travels in straight lines Light travels much faster than sound We see things because they reflect light into our eyes Shadows are formed when light is blocked by an object

The Electromagnetic Spectrum longest wavelength shortest wavelength The Electromagnetic Spectrum the name given to a group of energy waves that are mostly invisible and can travel through empty space The waves with the LONGEST wavelength (radio waves) are on the LEFT. The waves with the SHORTEST wavelength (gamma waves) are on the RIGHT.

What is the electromagnetic spectrum? The visible spectrum is just one small part of the electromagnetic spectrum. These electromagnetic waves are made up of two parts. The first part is an electric field. The second part is a magnetic field. So that is why they are called electromagnetic waves.

What’s the difference between sound waves and the electromagnetic waves? Electromagnetic waves are unlike sound waves because they do not need molecules to travel. This means that electromagnetic waves can travel through air and solid materials - but they can also travel through empty space. This is why astronauts on spacewalks use radios to communicate. Radio waves are a type of electromagnetic wave.

Characteristics of Radio waves: longest wavelength shortest wavelength Characteristics of Radio waves: Radio waves have a much longer wavelength than light waves. The longest waves are several kilometers in length. The shortest ones are only millimeters long. They are used for radio broadcasts, amateur radio, television, and mobile phones. Different parts of the radio spectrum have been allocated to the various services.

Characteristics of Microwaves: longest wavelength shortest wavelength Characteristics of Microwaves: shortest wavelength radio waves. absorbed by water molecules. What happens is that when the water in your TV dinner absorbs the microwaves, the energy of the microwaves is converted into heat: it makes the water molecules vibrate faster. Thus cooking your food.

Characteristics of Infrared waves: longest wavelength shortest wavelength Characteristics of Infrared waves: shorter wavelength than microwaves. felt as heat. hot objects give off infrared waves. 4. Animals like the pit-viper have infra-red detectors so that they can find their prey in the dark. You have been warned!!!

RedOrangeYellowGreenBlueIndigoViolet Visible light is a small portion of this spectrum. This is the only part of this energy range that our eyes can detect. What we see is a rainbow of colors. RedOrangeYellowGreenBlueIndigoViolet ROY G BIV

Characteristics of Visible light: longest wavelength shortest wavelength Characteristics of Visible light: shorter wavelength than infrared waves. can be seen as colors. ½ of sun’s rays are visible light.

Characteristics of Ultraviolet light: longest wavelength shortest wavelength Characteristics of Ultraviolet light: shorter wavelength than visible light. can kill living cells. causes skin cancer. 4.Some animals like honey bees can see ultra-violet light. Some plants have white flowers, at least you think that they are all white, but they may appear to be different colors to a honey bee because of the amounts of ultra-violet light which they reflect.

Characteristics of X-ray radiation: longest wavelength shortest wavelength Characteristics of X-ray radiation: harmful to humans. 2. X-Rays have so much energy and such a short wavelength that they can go right through you. However, they cannot get through bone as easily as they can get through muscle. This is because your bones contain so much Calcium.

Characteristics of Gamma radiation: longest wavelength shortest wavelength Characteristics of Gamma radiation: shortest wavelength (highest energy). from radioactivity or nuclear reactions. These are nasty ones. They have very high energy and will even go through metals. Gamma rays and X-Rays can cause cancer, but gamma rays can also be used to destroy cancer cells: this is radio-therapy.

Properties of Light Refraction- bending of light waves due to a change in speed

Properties of Light Refraction- bending of light waves due to a change in speed Lens- curved glass or transparent material that refracts light