PS20
Optics Pre Assessment
1. When light hits a plan mirror at an angle what statement is true.
a) The light will loose energy and bounce back along its own path.
b) The light will gain energy and bounce back at the same angle it hit the mirror.
c) The light energy should not change and bounce back at the same angle it hit the mirror.
d) The light energy should not change and bounce back along its own path.
2. Light that hits a convex mirror will..........
a) refract and cause the light to converge
b) reflect and cause the light to converge
c) refract and cause the light to diverge
d) reflect and cause the light to diverge
3. Light that hits a convex lens will..........
a) refract and cause the light to converge
b) reflect and cause the light to converge
c) refract and cause the light to diverge
d) reflect and cause the light to diverge
4. Light that hits a rectangular glass block at an angle will.....
a)
b)
c)
d)
refract and but not bend.
reflect and refract.
reflect only.
refract only.
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PS 20
Image Formation
Activity: Make a pin hole camera. The image can be described three ways
Size:____________________________
Attitude: _______________________
Type:_____________________________
The following formula can be used when dealing with a pinhole camera.
hi---- height of image on back of camera or film
ho---- height of object ( example the tree)
di— length of the pinhole camera
do— distance of object to the camera
Example:
A 35 cm long pinhole camera is used to take a picture of a tree 2.5 m tall. A 6.0 cm film paper is
used on the back of the camera. How far showed the camera be placed from the tree so the trees
image fits on the film?
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PS20
Plane Mirror
Complete the ray diagram to show how our eye sees point objects.
Complete the ray diagram to show how our eye sees large objects.
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Two Mirrors
How many images do two mirrors set at a right angle produce?
What do you think would happen if you changed the angles at which the mirrors were set up?
Periscopes
A simple periscope has two plane mirrors set up at 45 degree angles to each other. Draw a ray
diagram to determine how the eye sees the image.
Set up mirrors that are parallel to each other and are straight across? How many images do you
see?
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PS 20
Plane Mirror Questions
1. How does the image distance compare to the object distance.
2. Describe how you use light rays to show where an image in a plane mirror is located.
3. State the characteristics (size, attitude, type) of images in a plane mirror.
4. How many images are seen when two mirrors are place perpendicular to each other?
5. A plane mirror is placed 3.5 m in front of you. You look in it and see a virtual image of your
friend 4.7 m in the mirror. Assuming your friend is directly behind you, how far behind you is
the friend?
6. You run towards a plan mirror at 4.0 m/s. How fast is your image approaching you at?
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PS 20
Curved Mirrors Ray Diagrams
Concave mirror= Light rays converge
Convex mirror= light rays diverge
Ray Diagrams Rules for mirror
1.
2.
3.
Example1 : Converging mirror, C= 8.0 cm ( Note f = C/2)
ho= 1.5 cm
do= 9.0 cm
hi=?
di =?
Characteristic 1.
2.
3.
Example 2 : Converging mirror, C= 8.0 cm
ho= 1.2 cm
do= 6.0 cm
hi=?
di =?
Characteristic 1.
2.
3.
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PS20
Mirror Equation
Example 3 : Converging mirror, C= 10.0 cm
ho= 0.8cm
do= 4.0 cm
hi=?
di =?
Characteristic 1.
2.
3.
The Math
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Example 4 : Diverging mirror, f= -5.0 cm
ho= 2.0 cm
do= 7.0 cm
hi=?
di =?
Characteristic 1.
2.
3.
The Math
Example 5. A candle is 8 cm tall and placed 15 cm in front of curved mirror. A 20 cm virtual
image of the candle is produce by the mirror Find the radius of curvature of the mirror and type
of mirror.
Example 6. A person looks at Christmas tree bulb (diameter 12 cm) and sees that she is reduced
to 1/40 her size. Find how far the person is away from the bulb.
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PS20
Curved Mirror Questions
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1. Use careful scale drawings to locate the images (pick any height) in each of the following
cases. State the characteristics of each image.
(a) A converging mirror has a focal length of 20 cm. An object is placed at 30 cm from the vertex
of the mirror.
(b) A diverging mirror has a focal length of 20 cm. An object is placed 40 cm from the vertex of
the mirror.
2. A woman looks at herself in a magnifying converging mirror whose focal length is 20 cm. If
her face is 10 cm from the mirror,
(a) at what distance from the mirror is her image?
(b) what is the magnification of her face?
3. A 2.0 cm high candle is placed 15 cm in front of a converging mirror with a focal length of 30
cm. How far "behind" the mirror does the candle appear, and how large is it?
4. A dentist holds a converging mirror with a focal length of 20 mm a distance of 15 mm from a
tooth. What is the magnification of a filling in the tooth?
5. A trucker sees the image of a car passing her truck in her diverging rear-view mirror, whose
focal length is -60 cm. If the car is 1.5 m high and 6.0 m away, what is the size and location of
the image?
6. A spherical, polished metallic ball is used as a diverging mirror (f = -20 cm) over a birdbath. A
bird, 25 cm tall, standing 50 cm away, looks directly at the mirror. What are the size and position
of the bird's image?
7. When standing 2.0 m in front of an amusement park mirror, you notice that your image is three
times taller. What is the radius of curvature of the mirror?
8. A child looks at his reflection in a spherical Christmas tree ornament 8.0 cm in diameter, and
sees that the image of his of face reduced by one-quarter. How far is his face from the
9. A converging mirror has a focal length of 15 cm. Where would you place an object in order to
produce an erect virtual image five times as tall as the object?
Answer key
1. Varies
2.-20 cm, +2
3.-30 cm, 16 cm
4. 4
5.11 cm, -0.67
6.
7.
8.
9.
7.1 cm, -14.3 cm
6.0 cm
6.0 cm
12.0 cm
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PS20
Refraction and Snell’s Law
Activity1: Disappearing beaker
Activity 2: Reappearing penny
Activity 3: Ray box and glass blocks & Snell’s Laws
n= index of refraction (ratio speed of light in a vacuum to speed in material)
è= “theta” angle from normal in degrees
Common Index’s of Refraction
air= 1.00
water =1.33
glass= 1.52
diamond= 2.42
Example: 200 in air what angle will light enter in water? Glass?
Activity 4 : Internal Reflection
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PS20
Index of Refraction Questions
1. What is the angle of refraction when light enters glass from water. The angle of
incidence is 520.
2. What is the index of refraction of a material if light enters from air at 200 and refracts
in the material at 120?
3. Draw the path of light that enters and leaves a glass block. Assume the light enters
from air.
4. Bonus: For a challenge try to determine what angle the light comes out a glass
prism. See diagram.
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PS20
Lenses
Convex lens= Light rays converge
Concave lens= light rays diverge
Ray Diagrams Rules for Lenses
1.
2.
3.
Example1 : Converging Lens, f= 5.0 cm
ho= 1.5 cm
do= 8.0 cm
hi=?
di =?
Characteristic 1.
2.
3.
_____________________________________________________________________
The Math
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Example2 : Converging Lens, f= 6.0 cm
ho= 0.8 cm
do= 4.0 cm
hi=?
di =?
Characteristic 1.
2.
3.
_____________________________________________________________________
The Math
Example3 : Diverging Lens, f= -5.0 cm
ho= 2.0 cm
do= 7.0 cm
hi=?
di =?
Characteristic 1.
2.
3.
_____________________________________________________________________
The Math
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Example 4: A magnifying glass is used to enlarge an object by 6 times. If the focal length of the
lens is +4.0 cm. How far away is the object from the lens?
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PS20
Lens Questions
1 a. Draw a scale diagram for a converging lens with focal length of 4 cm. If and object is placed 7 cm
in front of the lens and is 1.5 cm tall, find the location and height of the image.
b. What are the characteristics of the image?
c. Verify with the lens equation the height and distance of the image?
d. What is the magnification of the image?
2 a. Draw a scale diagram for a concave lens with focal length of -4 cm. If and object is placed 6 cm in
front of the lens and is 2.0 cm tall, find the location and height of the image.
b. What are the characteristics of the image?
c. Verify with the lens equation the height and distance of the image?
d. What is the magnification of the image?
3 a. Draw a scale diagram for a converging lens with focal length of 3 cm. If and object is placed 2.3
cm in front of the lens and is 1.0 cm tall, find the location and height of the image.
b. What are the characteristics of the image?
c. Verify with the lens equation the height and distance of the image?
d. What is the magnification of the image?
4. Your wear glasses and hold them out in front of you. You look into the concave lens (f=-40 cm) and
find an object reduced one thirtieth its size, how far is the object from the lens ?
5. A convex lens produces a inverted image that is 4 cm tall from an object that is
24 cm tall. The object is 18 cm from the lens, find out the focal length of the lens?
6. A diverging lens with focal length of 30 cm produces an image that is 20 cm away form the lens. If
the object is 5.0 cm tall what is the height of the image?
7.A microscope with an objective lens (focal length 2.0 cm) and eyepiece lens(focal length 4.0 cm) are
15.0 cm apart. A 1.2 cm object is placed 2.4 cm in front of the object lens. Draw a scale diagram and
answer the following questions.
SHOW ALL YOUR WORK
a) What is the distance and height of image formed by the objective lens? (2)
b) What is the magnification and characteristics of the image in question "a"?(2)
c) What is the distance of the image (from question "a") in front of the of the eyepiece?(2)
d) What is the distance and height of the second image? (2)
e) What is the magnification and characteristics of the second image?(2)
f) What is the overall magnification of the image?(2)
Answer Key
1. Real larger inverted, 9.3 cm 2.0 cm, -1.33
2. Smaller virtual erect, -2.4 cm 0.8 cm, -0.4
3. Larger erect virtual, -9.8 cm 4.3 cm, -4.33
4. 116 cm
5. 2.57 cm
6. 60 cm
7. 12 cm 6.0 cm, 5, -12 cm -24 cm, -4, -20
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PS20
Two Lens Systems
Microscope
Telescope
Example 1
fo= 2.5 cm,
do=3.5 cm,
ho=1.5 cm, distance fo to fe= 10 cm, fe= 2.0 cm
do=4.5 cm,
ho=0.8 cm, distance fo to fe= 11 cm, fe= 3.5 cm
Example 2
fo= 3.0 cm,
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PS 20
Optics Pre Test
Part I fill in the blank
1. An image that can not be formed on a screen is called a ___________ image.
2. When a book is held against a plane mirror the letters are reversed horizontally but not
vertically, this is called _______________.
3. A surface that is highly __________ will act like a mirror.
4. In a converging mirror a object is placed between the focal point and the vertex, the image
will be _________, __________, and ____________.
5. A ray of light that strikes a curved polished surface parallel to the principal axis and does not
go through the principal focus is abnormal. This is called ______________.
6. The construction line that is drawn a right angles to the point of incidence of light ray is called
the _____________.
7. Parabolic mirrors are used in large telescopes to ___________________ light from a distant
star or plant onto the focal plane.
8. Rays of light that tend to spread apart are called ______________ rays.
9. The reason a diverging mirror is used in a drug store is a shopkeeper has a ________ field of
view.
10. If a object is placed between two parallel mirrors you will see ____________ images.
Part II Calculations and Drawings
1. The outside of a spoon has and average focal length of -5.0 cm. You look into the spoon and
see your eye it is one quarter your original. How far are you from the spoon?
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2. A convex mirror produces an erect image that is 5 cm tall from an object that is 60 cm tall.
The object is 1.2 m from the mirror, find out the radius of curvature for the mirror?
3. Draw a diagram to find the distance and height of an image. The object is 7cm away and has
height of 2 cm from a diverging lens. The lens has a focal point of -8 cm.
4. Draw the appropriate rays to find the focal point and centre(label these points).
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5. Draw all three rays and find the image distance, height, magnification and characteristics?
6. Draw the path of light to determine what angle the light leaves the block below. Assume the
light enters from air?
7. A microscope with an objective lens (focal length 2.5 cm) and eyepiece lens(focal length 3.5
cm) are 17.0 cm apart. A 1.5 cm object is placed 3.0 cm in front of the object lens. Find the
distance height of the eyepiece lens image (2nd image) and overall magnification of the
microscope.
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