NEET Ray Optics — Set 14

Question 1

In a convex lens, if an object is placed at the focal point, where is the image formed?

Accepted Answer

For a convex lens, when the object is at the focal point (F), the rays after refraction become parallel and do not converge to a point on the other side. The image is formed at infinity, as the rays appear to diverge from an infinitely distant point when traced backward.

Question 2

A ray of light passes from water ($ n = 1.33 $) to glass ($ n = 1.62 $) at an angle of incidence of $ 45^\circ $. What is the angle of refraction?

Accepted Answer

Snell’s law: $ n_1 \sin i = n_2 \sin r $. Water ($ n_1 = 1.33 $), glass ($ n_2 = 1.62 $), $ i = 45^\circ $. $ 1.33 \times \sin 45^\circ = 1.62 \times \sin r $. $ \sin 45^\circ = 0.707 \Rightarrow 1.33 \times 0.707 = 1.62 \sin r \Rightarrow 0.941 = 1.62 \sin r $. $ \sin r = \frac{0.941}{1.62} \approx 0.581 \Rightarrow r = \sin^{-1}(0.581) \approx 35.5^\circ $.

Question 3

In a concave lens, why is the image always formed on the same side as the object?

Accepted Answer

A concave lens diverges light rays, making them appear to originate from a point on the same side as the object when traced backward. This results in a virtual image that cannot be projected on a screen, always forming on the object’s side regardless of its position.

NEET Physics: Ray Optics — Practice Set 14

Q1. In a convex lens, if an object is placed at the focal point, where is the image formed?

Q2. A ray of light passes from water (\( n = 1.33 \)) to glass (\( n = 1.62 \)) at an angle of incidence of \( 45^\circ \). What is the angle of refraction?

Q3. In a concave lens, why is the image always formed on the same side as the object?

Q4. Why does the apparent depth of an object in a denser medium appear less than its real depth when viewed from air?

Q5. When light travels from a denser medium to a rarer medium and the angle of incidence exceeds a certain value, what phenomenon occurs?

Q6. What happens to the image formed by a convex mirror if the object is moved closer to the mirror from a distant position?

Q7. In a compound microscope, why is the final image inverted with respect to the object?

Q8. A convex lens (\( f = 60 \, \text{cm} \)) and a concave lens (\( f = 30 \, \text{cm} \)) are in contact. What is the effective focal length?

Q9. An object is placed \( 12 \, \text{cm} \) from a convex mirror of focal length \( 20 \, \text{cm} \). What is the magnification?

Q10. A concave lens of focal length \( 10 \, \text{cm} \) forms an image \( 5 \, \text{cm} \) from the lens. What is the object distance?