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A girl was playing with a thin beam of light from her laser torch by directing it from different directions on a convex lens held vertically. She was surprised to see that in a particular direction the beam of light continues to move along the same direction after passing through the lens.

1. What is the reason?

a. The girl must have directed the ray of light along the direction of the optical centre of the lens.

b. The girl must have directed the ray of light along the direction of the focus of the lens.

2. A convex lens of focal length 10 cm is placed at a distance of 14 cm from a wall. How far from the lens should an object be placed so as to form its real image on the wall?

a. 40 cm

b. 50 cm

c. 60 cm

d. 70 cm

3. If an object of 7 cm height is placed at a distance of 14 cm from a convex lens of focal length 8 cm. What is the nature of the image?

a. Real and erect

b. Real and inverted

c. Virtual and erect

d. Virtual and inverted

4. Where should an object be placed in front of a convex lens to get a real image of the size of the object?

a. At the principal focus of the lens.

b. At twice the focal length.

c. At infinity

d. Between the optical centre of the lens and its principal focus.

5. Focal length of convex lens is 

a. Negative

b. Positive

1 Answer

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1. a. The girl must have directed the ray of light along the direction of the optical centre of the lens.

2. c. 60 cm

3. b. Real and inverted

4. b. At twice the focal length.

5. b. Positive

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