## Physics - Refraction From Lens

Q1: In refraction of light, what does Snell's Law state?

Answer: The ratio of sine of angle of incidence to the sine of angle of refraction remains constant subject to certain conditions. This is called refraction.

Q2: Which of the following property of light wave changes when it travels from one medium to another (having different optical densities)?

a. Wavelength
b. Speed of Light
c. Frequency

Answer: The frequency of a wave does not change as the wave passes from one medium to another. Both the speed and the wavelength do change, but the frequency remains the same.

Q3: Which of the following correctly represents the Snell's Law equation:
a. n₁sinθ₁ = n₂sinθ₂
b. n₁sinθ₂ = n₂sinθ₁
c. n₁tanθ₂ = n₂tanθ₁

Answer:  Option 'a' is correct i.e.  n₁sinθ₁ = n₂sinθ₂

Q4: What is the relation between aperture and radius of curvature of a typical thin lens?

Answer:  Aperture is much less than its radius of curvature for a thin lens.

Q5: When a ray of light passes through the optical centre (O) of a convex or concave lens, how will it emerge?

Answer: The emergent ray will have no deviation.

Q6: Fill in the blank.
The _______ length is the image distance that corresponds to an infinite object distance.

Answer: Focal length (Use lens formula, put v = ∞)

Q7:  When the object is between the focal point and a converging lens, where and what type of image will be formed?

Answer: When the object is between the focal point and a converging lens, the image is virtual, erect, larger than the object, and on the front side of the lens.

Q8: If the lens is used to form an image of the Sun on a screen, how far from the lens should the screen be located?

Q9: Take a concave lens and place it on the lens stand. Keep a burning candle on one side of the lens, observe its image by looking from the other side of the lens. Can you obtain the image on a screen? Why or Why not?

Answer:  It cannot be obtained on a screen. A concave lens always forms virtual, erect and diminished image irrespective of the object.

Q10: What is the power of a convex lens?

Q11: If a concave lens has power -2D, what is its focal length?

Q12: Magnification (m) for a concave lens is + 0.33. What type of image so formed?

Answer: The positive sign shows that the image is erect and virtual. The image is one-third of the size of the object.

Q13: What is the SI unit of power of a lens?

Q14: Can a converging lens be made to diverge light? Say, if we place it in a liquid, how?

Answer: If a converging lens is placed in a liquid having an index of refraction larger than that of the lens material, the direction of refraction at the lens surfaces will be reversed, and the lens will diverge light.

Q15: Can I use lens used for myopia to fire a piece of paper by focusing the image of the sun?

Answer: No. Glasses used for myopia are diverging lens (concave), light cannot be focussed at a point.  