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Characteristics of image formed by plane mirror
This is due to different colours travelling different speeds in glass.
A thicker lens has a shorter focal length and bends light rays to a greater extent whereas a thinner lens has a longer focal length and bends light rays to a shorter extent.
Linear magnification = height of image / height of object OR image distance / object distance
Constructing ray diagrams
2. The diagram shows a ray of light moving from air to plastic. Which ratio is the refractive index of plastic?
3. The image seen on the translucent screen of a pinhole camera is
a. real and inverted
b. real and upright
c. virtual and inverted
d. virtual and upright
4. An object is placed in front of a pinhole camera. An image is seen at the centre of the translucent screen when viewed from behind. If the object is now moved slightly nearer and to the observer's right, the image becomes
a. larger and moves to the observer's right
b. larger and moves to the observer's left
c. smaller and moves to the observer's right
d. smaller and moves to the observer's left
5. A light ray does not undergo refraction at a boundary between two media of different optical densities if its angle of incidence is
6. An object is placed in front of a lens at a distance less than the focal length of the lens.
The image formed will be
a. real, inverted and diminished
b. real, upright and magnified
c. virtual, inverted and magnified
d. virtual, upright and magnified
7. If the size of the image formed by a converging lens is the same as the object, the object distance is
a. less than the image distance
b. equal to the image distance
c. less than the focal length of the lens
d. equal to the focal length of the lens
8. Which of the following instruments does not contain lenses?
9. A boy walks at a speed of 5m/s towards a plane mirror. The boy and his image in the mirror are moving
a. towards each other at a speed of 5m/s
b. away from each other at a speed of 5m/s
c. towards each other at a speed of 10m/s
d. away from each other at a speed of 10m/s
10. The size of an image formed in a pinhole camera may be increased by
a. placing the object nearer to the camera
b. reducing the size of the object
c. decreasing the distance between the pinhole and the screen
d. making the pinhole bigger
11. In total internal reflection, the angle of incidence is
a. less than the critical angle
b. greater than the critical angle
c. less than the angle of reflection
d. greater than the angle of reflection
12. Total internal reflection can take place in glass and not in air because glass is
a. optically denser than air
b. less transparent than air
c. more transparent than air
d. as optically dense as air
13. The image formed by a slide projector is usually
a. real, inverted and diminished
b. real, inverted and magnified
c. virtual, upright and magnified
d. virtual, inverted and diminished
14. Red light cannot be dispersed by a glass prism because it
a. has a high frequency
b. has a long wavelength
c. does not have component colours
d. is not refracted in glass
15. White light is dispersed using a prism by means of
16. A student uses a converging lens to produce an enlarged virtual image of a scale she wishes to read accurately. The focal length of the lens is 10cm. What is a suitable distance between the scale and the lens?
17. Which of the following is/are optical device(s) that uses a lens to form a real image of an object?
(1) magnifying glass
(2) pinhole camera
(3) slide projector
a. (3) only
b. (1) and (2) only
c. (1) and (3) only
d. (2) and (3) only
1. An observer E stands near the edge of a swimming pool. He could see the image of a lamp L1 due to the reflection of light from the surface of the water, which acts like a mirror. L2 and L3 are two other lamps fixed as shown below.
a. On the diagram, mark the position of the image of L1.
b. Draw two rays to show how E is able to see the image of L1.
c. State whether this image is real or virtual.
d. How would the position of the image of L1 seen by E be affected if the water level in the pool were lowered?
e. Can observer E see the image of L3?
1a and b.
d. The image will appear further. (because the distance between the lamp and water surface (mirror) is now increased)
e. Yes, the observer can see the image.
2. Figure a and b show light rays reflected to an observer from the surface of each of two mirrors, one plane and the other curved. The normal, N, at each point of incidence has been drawn.
a. Complete both diagrams by drawing accurately the incident rays that would produce the reflected rays shown. The incident rays should start from lines PQ and XY.
b. Write down the lengths of the portion of PQ and XY which observers A and B can see in the two mirrors respectively.
c. Give one reason why the side mirrors of most cars are curved.
b. AB: 3.3cm
c. Provide drivers with a wider field of vision
3. The diagram shows a person whose eyes are 1.6m above the ground. He looks at his reflection in a vertical plane mirror 2.5m away. The top and bottom of the mirror are 2.0m and 1.0m above the ground respectively.
a. How far behind the mirror is the image of the person's head?
b. The person holds the letters 'SET' in front of the mirror. Write down the image of these letters as seen by him.
c. By drawing light rays, indicate on the diagram which part of his body the person could not see in the mirror.
4. The diagram below is a scale drawing of a narrow road with a plane mirror mounted across the corner of a 90º bend. The point C represents a car.
a. Mark the position of the car image, formed by reflection at the mirror by a point I.
b. Draw the paths of two rays of light from C by which a man sees this image with his eye positioned as shown in the diagram.
The car travels towards the bend, along the centre line of the road, a distance represented by 10mm on the diagram.
c. Mark I' the position of the image of the car when it has travelled to this position.
d. Draw an arrow on the diagram to show the direction in which the car appears to the man to be travelling.
6. Two men, A and B, are standing in front of a plane mirror as shown.
a. What is the angle of incidence?
b. What is the angle between the incident ray and the reflected ray?
c. The plane mirror is lowered until the inclination is reduced to 20º. What is the change in angle of reflection?
5a. Angle of incidence is the angle between the normal and the incident ray.
Angle of incidence = 90º - 40º = 50º
5b. Angle of incidence = angle of reflection
Angle between the incident ray and the reflected ray = 50º + 50º = 100º
5c. Original angle of reflection = 50º
New angle of reflection = 70º
Change in angle of reflection = 70º - 50º = 20º
a. When A looks into the mirror, how far does B seem to be away from him?
b. B starts running towards A at a rate of 1m/s. How fast does B appear to be moving towards A when A looks at the mirror?
c. A starts running towards the mirror at 1m/s. When A looks at the mirror, how fast does his image appear to be moving towards him?
6a. distance between A and B' = 3 + 3 + 6 = 12m
6b. B will appear to be running towards A at a speed of 1m/s.
6c. A will appear to be running towards himself at a speed of 2m/s.
7. An artist leans his back against a painted wall while looking into a 1m long mirror at the opposite end of a rectangular room.
a. How many metres of the painted wall can he see in the 1m long mirror?
b. The artist moves forward such that he is 5m from the mirror. How many metres of the painted wall can he see in the 1m long mirror?
7a. Assume that the artist is facing the centre of the mirror. To see the maximum range, he has to look at the two extreme ends of the mirror. By applying angle of incidence = angle of reflection, the maximum length of the painted wall is 2m.
7b. Assume that the artist is facing the centre of the mirror. To see the maximum range, he has to look at the two extreme ends of the mirror. Applying the principle angle of incidence = angle of reflection,
DC = 0.5m
BD = 0.5m (ABC is an isoceles triangle)
Triangle ADB is similar to triangle AFE
AD/BD = AF/EF
5/0.5 = 15/EF
EF = 1.5m
GH = EF = 1.5m
The maximum length of the painted wall is 1.5m + 1m + 1.5m = 4m
8. A ray of light travels from air into a semicircular prism and emerges into the air again as shown below. The refractive index of air is 1.0.
9. An object O is placed in front of a thin converging lens of focal point F as shown below.
a. What is the critical angle of the prism material?
b. What is the refractive index of the prism material?
c. The light ray is rotated anti-clockwise causing such that angle a is changed to 50º. Draw on the diagram the new positions of the incident ray and refracted ray.
d. The light ray is rotated clockwise such that angle a is changed to 70º. Draw the new positions of the incident ray and refracted ray.
8a.critical angle = 90º - 60º = 30º
8b. sin c = 1/n
sin 30 = 1/n
n = 2.0
8d. ni sin i = nr sin r
2 x sin 20 = 1 x sin r
r = 43.2º
a. Complete the ray diagram to locate the position of the image formed by the converging lens.
bi. What are the characteristics of the image formed?
bii. Name an application for such an arrangement.
ci. What happens to the size and position of the image when the object is moved slightly to the left?
cii. Name an application for such as arrangement.
di. What happens to the size and position of the image when the object is moved slightly to the right?
dii. Name an application for such an arrangement.
9bi. real, inverted and same size as object
ci. The image gets smaller and image distance from the lens decreases.
di. The image gets bigger and image distance from the lens increases.
10. An object O is placed in front of a thin converging lens of focal point F as shown below.
a. In the diagram above, draw rays to locate the position of the image formed by the converging lens.
b. What are the characteristics of the image formed?
c. What happens to the size and position of the image when the object is moved nearer to the left, towards the focal point?
15b. virtual, upright, magnified
15c.The image gets bigger and image distance from the lens increases.
16. An object O is placed in front of a thin diverging lens of focal point F as shown below.
a. In the diagram above, draw rays to locate the position of the image formed by the diverging lens.
b. What are the characteristics of the image formed by a diverging lens?
c. What happens to the size and position of the image when the object is moved nearer to the diverging lens?
16b. virtual, upright, diminished
16c.The image gets bigger and image distance from the lens decreases.