Page 142 - Ripples SCIENCE 7 - TEJPUR Edition 2024 Answer Key

These are two types of optical media:

(a) Transparent medium  Allows light to pass through clearly, like clear glass or

water.

(b) Translucent medium  Allows some light to pass through it, but scatters it, like

frosted glass or wax paper.

7. The angle between the angle of incidence and the angle of reflection is 120°. Calculate

the angle of incidence and the angle of reflection.
Ans: Since, The angle between the angle of incidence & the angle of reflection is 120°.

∴ ∠i + ∠ r = 120°

Also, ∠i = ∠r

So, ∠i + ∠i = 120°

or 2 ∠i = 120°

or ∠i = ∠r = 60° [ ∠i = ∠r]
∴
8. With the help of a ray diagram show converging and diverging lens and name the

lenses.
Ans:

Focal Focal
Point Axis Axis Point

Focal length Focal length
Concave lens Convex lens
Spherical lenses Diverging and converging lenses

F. Long-answer questions.

1. Why is a concave lens known as a diverging lens whereas a convex lens is known as a

converging lens? Explain with a diagram.

Ans: When you hold the lenses in your hands, you will find that one lens is thicker in
the middle and the other is thicker at the edges. A convex lens is thicker in the

middle while a concave lens is thicker at the edges. A convex lens is also known as a

converging lens as it converges the light rays passing through it. A concave lens will

always give a virtual, erect and diminished image, irrespective of the position of the

object. It behaves like a convex mirror. This is because a convex lens, on the other

hand, will always give a real and inverted image except when the object is placed too

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