Light... ORB Education Quality Teaching Resources ORB Education Visit for the full, editable versions with solutions. ScP033.

Light...ORB Education Quality Teaching Resources

ORB Education Visit http://www.orbeducation.com.au for the full, editable versions with solutions.

ScP033 – Mixed PowerPoints

Consider the picture below…..

Why can the Belinda see the cat, but not the dog?

Belinda

This is also the reason why shadows occur when something gets in the way of the light.

Light travels in straight lines

Let’s start at the beginning….

This is why we cannot see around corners.

For you to be able to see an object, light must travel from the object to your eye.

The light that hits the object usually comes from somewhere else …

… maybe the Sun …

… or perhaps from a light bulb, candle or torch.

These are called ‘light sources’.

How do we see things?

It must then be reflected off the object and travel to your eyes.

How do we see things?

So, in order to see an object, light must travel from the source to the object

Belinda can see the cat.

This is because light from the source can reach the cat ...

… and the reflected light from the cat can travel in a straight line to Belinda’s eyes.

So, looking at that picture again...

Belinda can’t see the dog.

Even though light from the source can reach the dog ...

… the reflected light from the dog cannot travel straight to Belinda’s eyes.

So, looking at that picture again...

Can the girl see the person in the mask?

On your worksheet, draw light rays in order to determine whether she can or not.

NoAnd the answer …

Consider the picture below…..

• Light travels in lines that are …

… straight.

• Some things, such as the Sun and light bulbs give out their own light. These are called …

… light sources.

Other examples of light sources are …

… candles and torches.

Summary so far

… reflect the light that has come from a source.

• For you to see the object, this reflected light must be able to …

… travel in a straight line to your eyes.

Summary so far

• Most things don’t give out their own light. They simply …

A very smooth surface, such as a mirror or a still pond, will reflect a beam of light in one direction only.

Mirror

These thin beams of light are called ‘light rays’.

Reflection from Smooth Surfaces

This type of object is said to have a glossy (or shiny) surface.

A clear reflection is seen in the surface.

Most objects are not smooth, especially when viewed under a microscope.

In these cases, the light is reflected in all directions.

Reflection from Rough Surfaces

A clear reflection is not seen in the object.

Surface of Paper (under a microscope)

This type of object is said to have a ‘Matt’ surface.

… at exactly the same angle.

Mirror

700

700

Which brings us to the Law of Reflection

If a ray of light is directed at a mirror …

… at a certain angle …

… it will be reflected from the mirror …

Or, in more theoretical terms:

Which brings us to the Law of Reflection

200

200angle of reflection, r

angle of incidence, i

Normal

angle of incidenceangle i = angle r

= angle of reflection

Mirror

700

700

Show on your diagram what happens to the ray of light next.

400 400

Drawing Rays

Press the Spacebar when you have finished.

mirror

… and this ray of light?

300 300

Drawing Rays

Press the Spacebar when you have finished.

mirror

The law of reflection has been known for some time.

In fact, the pyramids in Egypt were decorated by people who understood it.

The artists working in the Pharaoh’s tomb needed to have enough light to see their painting.

The Pyramids

They didn’t use oil lamps or candles, because that would

have left marks on the walls from the dark smoke.

So that light could be reflected into

each chamber, polished metal

mirrors were placed along the

corridors!

The Pyramids

The light could then reflect all the way to the artist in

the tomb.

The amount of light reaching the burial chamber would have been very small.

The artists eyes, however, would have slowly adjusted to the small amount of light.

The Pyramids

When the artist left the tomb, the daylight would have seemed blindingly bright.

Unfortunately, each time light is reflected, some of it is absorbed. The light intensity would drop with each reflection.

In this way, the artist’s life was dedicated to the Pharaoh.

The Pyramids

Claire is performing a light experiment.

Using a ray box, she sends a ray of light towards a mirror.

Light Experiments

She can also trace the reflected ray.

She places a piece of paper underneath the ray box and mirror, so that she can mark in the direction of the ray before it strikes the mirror.

100

ray box 100

mirror

Using this information, fill in the table on your worksheet.

b. 200

c. 300

d. 450

e. 600

Light Experiments

Claire carries out the experiment five times, using different angles each time.

These are the angles she directed the ray from:

a. 100

Which angle must Claire have recorded incorrectly?

Answer: 450 / 550

Angle that light strikes the mirror

Angle that light reflects from the mirror

100

200

300 300

450

600

100

200

550

600

This is the table that Claire completed after measuring each of the angles.

Light Experiments

ORB Education Quality Teaching Resources

ORB Education Visit http://www.orbeducation.com.au for the full, editable versions with solutions.

ScP033 – Mixed PowerPoints

Remainder removed from this sample presentation.