PHYSICS 3

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PHYSICS 3
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Drawing Ray Diagrams (1)

• Draw one ray from the top of the object parallel
  to the centre axis. This is refracted through the
  principal focus.
• Draw a second ray through the centre of the lens.
  This passes straight on it is not refracted at
  all!
• Where the rays meet the image is formed.

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Drawing Ray Diagrams
Lens

• Two light rays leave the object O and pass
  through the lens. Where they meet an image I is
  produced. This is a REAL, DIMINISHED and INVERTED
  image.

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Convex Lens Ray Diagrams Object at 2F
Image is real, inverted and the same size as the
object.
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Convex Lens Ray Diagrams Object Between 2F and F
Image is real, inverted and magnified.
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Convex Lens Ray Diagrams Object Between F and C
Magnifying Glass
Image is virtual, upright and magnified.
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Using Convex Lenses
Wednesday, 25 December 2013

• Lesson objectives
• Know how a convex lens can be used as a
  magnifying glass.
• Be able to use a convex lens to produce
  magnified and diminished real images.

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Magnifying Glass

• The focal length of your lens is about 15 cm. Use
  your lens to focus an image of the outside on the
  white screen.
• You should obtain a real, inverted and diminished
  image the focal length away from the lens.
• Check this out for yourself.

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Using a Magnifying Glass

• When you place it nearer an object than the focal
  length it acts as a magnifying glass.
• You obtain a magnified, virtual, upright image!
• Check this out for yourself.

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Finding The Image
Move plane screen to see focused image
X- wire screen
Convex lens in holder
Distance v
Distance u
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Results
Distance from X-wire to lens, u (cm) Distance from Lens to focused image, v (cm) Description of Image
20
25
30
40
50
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Analysis Answer using complete sentences.

1. What is the condition to produce a magnified real
   image?
2. When is the image the SAME SIZE as the object?
3. What sort of image is produced in a camera?
4. Where must the object be placed for a camera to
   obtain its image?
5. Where must the object be placed in a projector?

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Optics Test
1. Which statement is true? A. Virtual images
can be projected onto screens B. Erect images
are upside-down C. Concave mirrors are diverging
D. Biconcave lenses are diverging
?
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Optics Test
2. Which statement is true? A. Diminished images
are smaller than the object B. Convex mirrors
are converging C. Biconvex lenses are diverging
D. Real images can not be projected onto
screens
?
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Optics Test
3. What optical device is shown? A. Biconvex
lens B. Biconcave lens C. Plane mirror
D. Concave mirror
?
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Optics Test
4. What optical device is shown? A. Biconvex
lens B. Biconcave lens C. Convex mirror
D. Concave mirror
?
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Optics Test
5. What does the diagram demonstrate? A.
Biconcave lenses are diverging B. Biconvex
lenses are converging C. Biconcave lenses are
converging D. Biconvex lenses are diverging
?
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Optics Test
6. What does the diagram demonstrate? A.
Concave mirrors are diverging B. Convex mirrors
are converging C. Concave mirrors are
converging D. Convex mirrors are diverging
?
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Optics Test
7. Which part of the eye detects light? A.
Cornea B. Lens C. Optic nerve D. Retina
?
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Optics Test
8. Which device can be used to correct for
short-sightedness? A. Concave
mirror B. Convex mirror C. Biconvex
lens D. Biconcave lens
?
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Optics Test
9. Which optical instrument is shown? A. A
compound microscope B. A magnifying glass
C. A refracting telescope D. A reflecting
telescope
?
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Optics Test
10. Which force limits the size of astronomical
refracting telescopes on Earth? A. Frictional
B. Electrostatic C. Gravitational
D. Magnetic
?
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The Eye
lens
vitreous humour
iris
aqueous humour
optic nerve
retina
cornea
ciliary muscle
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Eye Defects Long Sight
Long sightedness is when you can see distant
objects clearly but not close objects.
Long sightedness can be corrected using a convex
lens.
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