TECHNICIANS
INFORMATION
Equipment list
Risk Assessment
Lenses
Lens holder
Light box and slits
Power packs
Ruler
Risk:
Controlled by:
Burn from hot light box
Do not touch when hot
Sharps from dropping lenses Careful disposal of broken
glass.
Lesson SP5c: Lenses
Specification Extract
Separates
P5.5P: Use ray diagrams to show the similarities and differences in the refraction
of light by converging and diverging lenses
P5.6P: Explain the effects of different types of lens in producing real and virtual
images
P5.4P: Relate the power of a lens to its focal length and shape
RISK
ASSESSMENT
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5.
6.
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9.
10.
What is the normal?
Describe diffuse reflection?
State the law of reflection
Describe specular reflection?
Why do we see a green leaf as green?
Where do we measure the angle of incidence from?
Why will a light ray slow down and change direction?
Draw a ray of light passing through a glass block?
Why do we use colour filters?
A filter is blue, what happens to white light as it hits the
filter?
1. A line at right angles to the glass block or mirror.
2. Light reflecting off an uneven surface, light will not obey the
law of reflection, loss of detail.
3. The angle of incidence = the angle of reflection.
4. Light reflecting off a smooth surface, light obeys the law of
reflection, no loss of detail.
5. Only green light is reflected, the rest is absorbed.
6. The incident ray to the normal.
7. It enters a more dense medium.
8. Correct drawing.
9. To produce different lighting effects, stage, cinema.
10. Only blue light passes through the rest is reflected.
Lenses and Images
Learning Objectives
Describe the refraction of light by converging and diverging lenses
Describe real and virtual images
Relate the power of a lens to its shape
Increasing power
The power of a lens describes how large the angle of refraction
is as the light refracts through the lens. The larger the refraction,
the thicker the lens is, the more powerful the lens.
Two types of lens
Converging Lens
convex
Diverging Lens
concave
Why do we call it a
Converging lens?
Why do we call it a
Diverging lens?
A clue it is to do with light rays
Refraction of light through a diverging lens
A diverging lens, the focal point is the point from which
the waves seem to be coming from after passing through the lens.
Refraction of light through a converging lens
The focal point is where the rays of light meet after refraction.
The focal length is measured from the point to the middle of the lens.
With your ray boxes see how light behaves through the different lenses
What happens to the light when it refracts through this combination
Focal length of a lens
• Lets see if we can focus an image
• You will need
• Lens holder
• Ray box
• Powerpack
• Ruler
• Screen
• Different lenses
Set up equipment as shown.
Move screen back and too
until a clear crisp image is formed.
Bulb in ray box
Lens
>
>
Ray box
Lens holder
Screen
Focal length of a lens
• Using the keywords write how you find the focal length of a
lens.
Image
Lenses and Images
Learning Objectives
Describe the refraction of light by converging and diverging lenses
Describe real and virtual images
Relate the power of a lens to its shape
Two types of images can be created
A virtual image is one from which
the light rays appear to come but
don’t actually come from that image
like in a mirror.
A real image is the image formed
where the light rays are focussed
http://www.gcsescience.com/pwav27.htm
Image size and position
Object is at 2 focal lengths
Image is inverted
Image is the same size
Image is real
Object is at 1 focal lengths
No image is formed
Image size and position
Object is between 1 & 2 focal lengths
Image is inverted
Image is made bigger
Image is real
Image size and position
Object is at 2 focal lengths
Image is inverted
Image is the same size
Image is real
Image size and position
Less than one focal length
Image right way up
Image is smaller
Virtual image formed
Lenses and Images
Learning Objectives
Describe the refraction of light by converging and diverging lenses
Describe real and virtual images
Relate the power of a lens to its shape
x
>
>
Quick Quiz
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7.
Draw the rays of light through a diverging lens
What is a virtual image
How do you find the focal length of a lens
If the object is at 1 focal length describe the image
Give two factors which will increase the power of a lens
Draw light rays through a converging lens
Label the focal length and focal point