Light and Sound

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Light and Sound

• In this unit
• Properties of light
• Reflection
• Colours
• Refraction
• Properties of sound
• Hearing

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Part 1 Properties of Light

• Light travels in straight lines

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• Light travels VERY FAST around 300,000
  kilometers per second.

At this speed it can go around the world 8 times
in one second.
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• 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.

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• We see things because they reflect light into our
  eyes

Homework
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• 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
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• Shadows

Shadows are places where light is blocked
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Energy in Light

• -There is a lot of energy in light.
• -For example, when you stand in the sun you feel
  the suns energy through heat.
• -If you absorb too much of that energy, you can
  get a sunburn.
• -A lamp doesnt have as much energy as the sun-
  you cant get sunburned by a lamp.
• -However, a lamp does give off heat because of
  the electric current it takes to make it work.

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Properties of Light summary

1. Light travels in straight lines.
2. Light travels much faster than sound.
3. We see things because they reflect light into our
   eyes.
4. Shadows are formed when light is blocked by an
   object.
5. Light gives off energy in the form of heat.

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Part 2 Reflection

• -When light hits an object, the object affects
  the path of the light.
• -An object can absorb light, make it bounce off,
  or let it pass through.
• -Some light energy is absorbed. Darker objects
  absorb more light energy-thats why you are
  hotter when you wear dark colors on a hot day.
• -Objects dont absorb all the light that hits
  them. Some of the light bounces off. Reflection
  is the bouncing of light from a surface.

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Part 2Reflection

• -Usually, light scatters in many directions when
  it is reflected.
• -A smooth surface reflects light in a clear and
  predictable pattern.
• -Have you ever seen a reflection in clear windows
  on a building?
• -Looking in a mirror can also get you a smooth
  reflection, but it gives you a backward image.

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• Reflection from a mirror

Normal
Reflected ray
Incident ray
Angle of reflection
Angle of incidence
Mirror
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• 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 !!!
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Refraction
When light moves from water to air, its speed
changes. The change in speed makes the beam of
light bend. This bending of light is called
refraction. Refraction is bending light. When a
pen is placed in water it looks like
this Refracted light can make a solid object
look like it is broken into two parts. It looks
like that because the light from the part of the
pencil that is under the water reaches your eyes
on a different path.
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Translucent Materials
-Materials that let some light through are called
translucent. An example of a translucent
material is a frosted light bulb.
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Transparent Materials
-A transparent material allows most of the light
that hits it to pass through it. -Most glass,
water, and some plastics are transparent. -Transpa
rent objects dont scatter light, but they do
refract it.
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Opaque Materials
-Materials that do not allow any light to pass
through them are opaque. -Opaque materials absorb
all the light into them. -Metal, wood, and most
of your body is opaque.
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Color

• White light is not a single color it is made up
  of a mixture of the seven colors of the rainbow.

We can demonstrate this by splitting white light
with a prism
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Light and Color
-As light enters a prism, the light waves change
directions and separate (this is an example of
refraction). -You are able to see all the colors
of the rainbow when the colors separate. -You can
remember all the colors of the rainbow with
ROYGBIV. -When have you seen a rainbow of color?
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The colors of the rainbow

• Red
• Orange
• Yellow
• Green
• Blue
• Indigo
• Violet

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Lenses
-A lens is a curved, transparent object that
refracts light. -There are different types of
lenses with different types of curves.
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Convex Lens
-A convex lens is thicker in the middle than at
the edges. -As light waves move through the lens,
they bend towards the thickest part-the
middle. -A convex lens makes light waves come
together and make objects appear larger or
magnified.
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Concave Lens
-A concave lens is thicker at the edges than in
the middle. -As light waves enter the lens, they
bend toward the thicker part- the ends. -The
concave lens makes light waves spread out and
this makes objects appear smaller.
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Adding colours

• White light can be split up to make separate
  colours. These colours can be added together
  again.
• The primary colours of light are red, blue and
  green

Adding blue and red makes magenta (purple)
Adding blue and green makes cyan (light blue)
Adding all three makes white again
Adding red and green makes yellow
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Seeing colour

• The colour an object appears depends on the
  colours of light it reflects.

For example, a red book only reflects red light
White light
Only red light is reflected
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A pair of purple trousers would reflect purple
light (and red and blue, as purple is made up
of red and blue)
Purple light
A white hat would reflect all seven colours
White light
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Using coloured light

• If we look at a coloured object in coloured light
  we see something different. For example,
  consider a football kit

Shirt looks red
White light
Shorts look blue
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• In different colours of light this kit would look
  different

Red light
Shirt looks red
Shorts look black
Shirt looks black
Blue light
Shorts look blue
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Some further examples
Object Colour of light Colour object seems to be
Red socks Red Red
Red socks Blue Black
Red socks Green Black
Blue teddy Red Black
Blue teddy Blue
Blue teddy Green
Green camel Red
Green camel Blue
Green camel Green
Magenta book Red
Magenta book Blue
Magenta book Green
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Using filters

• Filters can be used to block out different
  colours of light

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Investigating filters
Colour of filter Colours that could be seen
Red
Green
Blue
Cyan
Magenta
Yellow
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Red
White
Blue
Green
Magenta
Yellow
Cyan
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Sound The basics
We hear things when they vibrate. If something
vibrates with a high frequency (vibrates very
______) we say it has a _____ pitch. If something
vibrates with a low frequency (vibrates ______)
we say it has a ____ pitch. The lowest frequency
I could hear was Words slowly, low, high,
quickly
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Drawing sounds
This sound wave has a _____ frequency
This sound wave has a ___ _frequency
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Drawing sounds
This sound wave has a _____ amplitude (loud)
This sound wave has a _____ amplitude (quiet)
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Hearing problems

• Our hearing range can be damaged by several
  things
• Too much ear wax!
• Damage to the auditory nerve
• Illness or infections
• Old age (not like Mr Richards)

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Other sound effects

• Like light, sound can be
• Reflected sound reflections are called ______.
• Refracted this is why you might sound strange
  if you try talking underwater

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The Ear
Label your diagram with the following These
bones are vibrated by the eardrum This tube
carries the sound towards the eardrum This part
is used to help us keep our balance This part
picks up the vibrations This part of the ear
contains many small hairs with turn vibrations
into an electrical signal This part connects the
ear to the mouth This part channels the sound
towards the ear drum
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The Ear