Q. A beam of light in glass (n=1.5) strikes the glass-air interface at an angle of 60°. What happens to the light?
A.It is refracted into the air.
B.It undergoes total internal reflection.
C.It is absorbed by the glass.
D.It is scattered.
Solution
Since the angle of incidence (60°) is greater than the critical angle (approximately 41.8° for glass to air), total internal reflection occurs.
Correct Answer: B — It undergoes total internal reflection.
Q. A beam of light in glass (n=1.5) strikes the glass-air interface at an angle of 60°. Will total internal reflection occur?
A.Yes
B.No
C.Only if the angle is increased
D.Only if the angle is decreased
Solution
To determine if total internal reflection occurs, we first find the critical angle using sin(θc) = 1/n = 1/1.5, which gives θc ≈ 41.8°. Since 60° > 41.8°, total internal reflection will not occur.
Correct Answer: B — No
Q. A beam of light passes through a thin convex lens with a focal length of 15 cm. If the object is placed 30 cm from the lens, what is the image distance?
A.10 cm
B.15 cm
C.20 cm
D.30 cm
Solution
Using the lens formula, 1/f = 1/v - 1/u; here, f = 15 cm and u = -30 cm. Thus, 1/v = 1/15 + 1/30 = 1/10, giving v = 10 cm.
Correct Answer: C — 20 cm
Q. A convex lens has a focal length of 15 cm. What is the power of the lens?
A.+6.67 D
B.+7.5 D
C.+10 D
D.+15 D
Solution
Power (P) = 1/f (in meters). f = 0.15 m, so P = 1/0.15 = +6.67 D.
Correct Answer: B — +7.5 D
Q. A fiber optic cable uses total internal reflection to transmit light. What is the primary requirement for this to work effectively?
A.The core must have a higher refractive index than the cladding
B.The cladding must have a higher refractive index than the core
C.The light must be monochromatic
D.The cable must be straight
Solution
For total internal reflection to occur in a fiber optic cable, the core must have a higher refractive index than the cladding.
Correct Answer: A — The core must have a higher refractive index than the cladding
Q. A fiber optic cable uses total internal reflection. What is the role of the cladding?
A.To increase the refractive index.
B.To decrease the refractive index.
C.To prevent light loss.
D.To enhance light absorption.
Solution
The cladding has a lower refractive index than the core, ensuring that light is kept within the core through total internal reflection.
Correct Answer: C — To prevent light loss.
Q. A lens forms a virtual image at a distance of 10 cm when the object is placed at 5 cm. What type of lens is it?
A.Convex lens
B.Concave lens
C.Bifocal lens
D.Plano-convex lens
Solution
A virtual image is formed by a concave lens when the object is placed within its focal length.
Correct Answer: B — Concave lens
Q. A lens forms a virtual image at a distance of 12 cm when the object is placed at 8 cm. What is the focal length of the lens?
A.4 cm
B.6 cm
C.8 cm
D.10 cm
Solution
Using the lens formula, 1/f = 1/v - 1/u, we find f = 4 cm.
Correct Answer: A — 4 cm
Q. A lens forms a virtual image at a distance of 20 cm from the lens when the object is placed at 10 cm. What is the focal length of the lens?
A.5 cm
B.10 cm
C.15 cm
D.20 cm
Solution
Using the lens formula 1/f = 1/v - 1/u, where v = -20 cm and u = -10 cm, we find f = 5 cm.
Correct Answer: A — 5 cm
Q. A lens has a focal length of +20 cm. What type of lens is it?
A.Concave lens
B.Convex lens
C.Bifocal lens
D.Cylindrical lens
Solution
A positive focal length indicates that the lens is a convex lens, which converges light rays.
Correct Answer: B — Convex lens
Q. A lens has a power of +2 diopters. What is its focal length?
A.0.5 m
B.1 m
C.2 m
D.3 m
Solution
Power (P) is given by P = 1/f (in meters). Thus, f = 1/P = 1/2 = 0.5 m.
Correct Answer: B — 1 m
Q. A lens has a power of +2.5 D. What is its focal length?
A.40 cm
B.25 cm
C.50 cm
D.20 cm
Solution
Power (P) = 1/f (in meters). Therefore, f = 1/2.5 = 0.4 m = 40 cm.
Correct Answer: B — 25 cm
Q. A lens has a power of +5 diopters. What is its focal length?
A.20 cm
B.25 cm
C.30 cm
D.15 cm
Solution
Power (P) = 1/f (in meters). Therefore, f = 1/P = 1/5 = 0.2 m = 20 cm.
Correct Answer: A — 20 cm
Q. A lens has a power of -4 D. What type of lens is it?
A.Convex lens
B.Concave lens
C.Bifocal lens
D.Plano-convex lens
Solution
A negative power indicates that the lens is a concave lens.
Correct Answer: B — Concave lens
Q. A light ray passes from air into glass with a refractive index of 1.5. If the angle of incidence is 30 degrees, what is the angle of refraction?
Q. A light ray traveling in a medium with n=2.0 strikes a boundary with air at an angle of incidence of 45°. What will be the angle of refraction in air?
A.22.5°
B.45°
C.60°
D.90°
Solution
Using Snell's law, n1 * sin(θ1) = n2 * sin(θ2). Here, n1 = 2.0, θ1 = 45°, and n2 = 1.0 (air). Thus, 2.0 * sin(45°) = 1.0 * sin(θ2) leads to sin(θ2) = √2, which gives θ2 = 90°.
Correct Answer: D — 90°
Q. A light ray traveling in diamond (n=2.42) strikes the diamond-air interface. What is the critical angle?
A.24.4°
B.36.9°
C.42.5°
D.49.5°
Solution
Using sin(θc) = n2/n1, where n1 = 2.42 (diamond) and n2 = 1.0 (air), we find sin(θc) = 1.0/2.42, leading to θc ≈ 24.4°.
Correct Answer: A — 24.4°
Q. A ray of light in glass (n=1.5) strikes the glass-air interface at an angle of 30°. What will be the angle of refraction in air?
Q. A ray of light passes from air into glass at an angle of incidence of 30 degrees. If the refractive index of glass is 1.5, what is the angle of refraction?
Q. A ray of light strikes a plane mirror at an angle of incidence of 30 degrees. What is the angle of reflection?
A.30 degrees
B.45 degrees
C.60 degrees
D.90 degrees
Solution
According to the law of reflection, the angle of reflection is equal to the angle of incidence. Therefore, the angle of reflection is 30 degrees.
Correct Answer: A — 30 degrees
Q. If a beam of light passes through a prism with an angle of 60 degrees and the refractive index of the prism is √3, what is the angle of minimum deviation?
A.30 degrees
B.60 degrees
C.45 degrees
D.15 degrees
Solution
Using the formula for minimum deviation, D = (n - 1)A. Here, n = √3 and A = 60 degrees. Thus, D = (√3 - 1) * 60 degrees, which approximates to 30 degrees.
Correct Answer: A — 30 degrees
Q. If a concave lens has a focal length of -10 cm, what is the nature of the image formed when the object is placed at 5 cm?
A.Real and inverted
B.Virtual and upright
C.Real and upright
D.Virtual and inverted
Solution
Concave lenses always produce virtual and upright images.
Correct Answer: B — Virtual and upright
Q. If a concave lens has a focal length of -10 cm, what is the nature of the image formed when an object is placed at 5 cm from the lens?
A.Real and inverted
B.Virtual and upright
C.Real and upright
D.Virtual and inverted
Solution
Concave lenses always produce virtual and upright images.
Correct Answer: B — Virtual and upright
Q. If a concave lens has a focal length of -20 cm, what is the nature of the image formed when an object is placed at 30 cm from the lens?
A.Real and inverted
B.Virtual and upright
C.Real and upright
D.Virtual and inverted
Solution
For a concave lens, the image formed is virtual and upright when the object is placed beyond the focal length.