# Shadows Shadows are places where light is “blocked”: Rays of light.

## Presentation on theme: "Shadows Shadows are places where light is “blocked”: Rays of light."— Presentation transcript:

Luminous and non-luminous objects
A luminous object is one that produces light. A non-luminous object is one that reflects light. Luminous objects Reflectors

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

Reflection Reflection from a mirror: Mirror Normal Angle of incidence
Incident ray Reflected ray Angle of incidence Angle of reflection Mirror

Angle of incidence = Angle of reflection
The Law of Reflection Angle of incidence = Angle of reflection In other words, light gets reflected from a surface at ____ _____ angle it hits it. The same !!!

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

Using mirrors Two examples: 2) A car headlight 1) A periscope

Colour White light is not a single colour; it is made up of a mixture of the seven colours of the rainbow. We can demonstrate this by splitting white light with a prism: This is how rainbows are formed: sunlight is “split up” by raindrops.

Only red light is reflected
Seeing colour The colour an object appears depends on the colours of light it reflects. For example, a red book only reflects red light: Homework White light Only red light is reflected

A white hat would reflect all seven colours:
Seeing Colour: A pair of purple trousers would reflect purple light ( i.e. red and blue light, as purple is made up of red and blue): Purple light A white hat would reflect all seven colours: White light

Refraction through a glass block:
Wave slows down and bends towards the normal due to entering a more dense medium Wave slows down but is not bent, due to entering along the normal Wave speeds up and bends away from the normal due to entering a less dense medium

Words – speed up, water, air, bent, medium
Refraction Refraction is when waves ____ __ or slow down due to travelling in a different _________. A medium is something that waves will travel through. When a pen is placed in water it looks like this: In this case the light rays are slowed down by the water and are _____, causing the pen to look odd. The two mediums in this example are ______ and _______. Words – speed up, water, air, bent, medium

Examples of Refraction
Is the fish deeper or shallower than its image appears to be? Should you stab above or below the image of the fish to spear it?

Examples of Refraction
Explain why: You can’t see the coin in the cup without water You can see the coin in the cup with water

Speed of sound The speed of sound in air is around 330 m/s. What happens when sound travels through different materials? Speed of sound (in m/s) Material Conclusion – the denser the material, the faster sound travels through it

Making Sounds A sound is made when an object or material VIBRATES.
Take, for example, a guitar. To make a sound with a guitar a string has to vibrate. We can raise the pitch of the sound a guitar makes by doing three things: 1) _________ the length of the string 2) _________ the string 3) Using a _________ string We can make the sound louder by ________ the string harder Words – tightening, thinner, increasing, plucking

Using an oscilloscope 1) Quiet sound, low frequency:
2) Quiet sound, high frequency: 3) Loud sound, low frequency: 4) Loud sound, high frequency:

How sound travels… As we know, sound waves are formed when something vibrates. But how does the sound reach our ears? Air molecules 2) The vibrations pass through air by making air molecules vibrate 3) These vibrations are picked up by the ear 1) An object makes a sound by vibrating

How does the ear work? 1) Sound waves are “funnelled” into the ear by the pinna 5) The electrical signals are then sent to the brain 3) These vibrations make the ear bones vibrate 4) These vibrations are turned into electrical signals in the cochlea 2) These vibrations make the ear drum vibrate

The Eye Read the definitions on the next slide, then label the eye anatomy diagram below.

The Eye Definitions Cornea - the clear, dome-shaped tissue covering the front of the eye. Iris - the colored part of the eye - it controls the amount of light that enters the eye by changing the size of the pupil Lens - a crystalline structure located just behind the iris - it focuses light onto the retina Optic nerve - the nerve that transmits electrical impulses from the retina to the brain Pupil - the opening in the center of the iris- it changes size as the amount of light changes (the more light, the smaller the hole) Retina - sensory tissue that lines the back of the eye. It contains millions of photoreceptors (rods and cones) that convert light rays into electrical impulses that are relayed to the brain via the optic nerve Vitreous - a thick, transparent liquid that fills the center of the eye - it is mostly water and gives the eye its form and shape (also called the vitreous humor)

Light Waves Light energy travels in the form of a transverse wave. Below is a picture of a light wave

Sound Waves Sound energy travels in the form of a longitudinal wave
Sound Waves Sound energy travels in the form of a longitudinal wave. Below is a picture of a longitudinal wave travelling along a spring.

Sound Waves When a longitudinal wave moves through a material, the particles of the material move backwards and forwards along the direction in which the wave is travelling.