Light reflection and refraction Worksheet-16

Light reflection and refraction Worksheet-16

1. A coin in a glass beaker appears to rise as the beaker is slowly filled with water. Why ?

2. A tank of water is 4 m deep. How deep does it appear when seen normally?

3. What is meant by optical centre of a lens ?

4. Define first principal focal length of a convex lens.

5. What is the difference between a real image and a virtual image?

6. What is linear magnification produced by a lens? How is it related to object distance and image distance?

7. When is magnification positive or negative?

8. What is the range of wavelength of visible light ? Which color has the largest wavelength which one has the shortest wavelength ?

9. Can light travel through vacuum? If yes, with what speed? Which colour travels the fastest ?

10. How is refractive index of a medium related to velocity of light in the medium ?

Answer:

1. It is because of refraction of light. A ray of light starting from the coin goes from water to air and bends away from normal. Therefore, bottom of the beaker on which the coin lies appears to be raised.

2. As refractive index

∴

The tank appears to be 3 m deep only.

3. The optical centre of a lens is a point on the principal axis of the lens, such that a ray of light passing through it goes undeviated.

4. The first principal focal length of a convex lens is the distance of first principal focus of the lens from optical centre of the lens. And first principal focus of a convex lens is the position of a point object on the principal axis of the lens, for which the image formed by the lens is at infinity.

5. A real image can be taken on a screen, because the refracted rays actually meet at a point on the screen. A virtual image cannot be taken on a screen, because the refracted rays only appear to come from a point and do not meet there actually.

6. Linear magnification produced by a lens is the ratio of size of image (h₂) to the size of the object (h₁). It is represented by m

7. When the image formed is virtual and erect, magnification is positive. And, when the image formed is real and inverted, magnification is negative.

8. The wavelength of visible light varies from 4 × 10^–7 m to 8 × 10^–7 m.

The red color has the largest wavelength (≈ 8 × 10^–7 m) and violet color has the shortest wavelength (≈ 4 × 10^–7 m).

9. Yes, light can travel through vacuum. The speed of light in vacuum is 3 × 10⁸ m/s. All the colours of visible light pass through vacuum with the same speed.

10. refractive index of a medium (n)

As c is fixed, therefore, For a rarer medium, n is smaller, therefore v is larger, i.e., light travels faster in a rarer medium than in a denser medium.