• Shadows

Shadows are places where light is “blocked”:

Rays of light

• 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:

Incident ray

Normal

Reflected ray

Angle of incidence

Angle of reflection

Mirror

• The Law of ReflectionThe Law of Reflection

Angle of incidence = Angle of Angle of incidence = Angle of reflectionreflection

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:

1) A periscope

2) A car headlight

RefractionRefraction is when waves ____ __ or slow down due to travelling in a different _________. A medium is something that waves will travel through. When a pencil is placed in water it looks like this:

In this case the light rays are slowed down by the water and are _____, causing the pencil to look odd. The two mediums in this example are ______ and _______.

Words – speed up, water, air, bent, medium

Refraction through a glass Refraction through a glass block:block:

Wave slows down and bends towards the normal due to

entering a more dense medium

Wave speeds up and bends away from the normal due to entering a less dense

medium

Wave slows down but is not bent, due to

entering along the normal

Examples of RefractionIs 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 RefractionExplain why:

You can’t see the coin in the cup without water

You can see the coin in the cup with water

Speed of soundThe speed of sound in air is around 330 m/s. What happens when sound travels through different materials?

0

1000

2000

3000

4000

5000

Air Water Brick I ron Material

Speed of

sound

(in m/s)

Conclusion – the denser the material, the faster sound travels through it

Making SoundsA 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 _________ stringWe can make the sound louder by ________ the string harder

Words – tightening, thinner, increasing, plucking

Using an oscilloscope1) 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?

1) An object makes a sound by vibrating

2) The vibrations pass through air by making air molecules vibrate

3) These vibrations are picked up by the ear

Air molecules

How does the ear work?1) Sound waves are “funnelled” into the ear by the pinna

4) These vibrations are turned into electrical signals in the cochlea

2) These vibrations make the ear drum vibrate

3) These vibrations make the ear bones vibrate

5) The electrical signals are then sent to the brain

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 pupilLens - 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. 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.