1–4. Introduction, Meaning and Cause of Refraction
Introduction to Refraction of Light Refraction is one of the central ideas of ray optics. It explains bending of light at transparent boundaries and is used in lenses, prisms, glass slabs, optical fibres, atmospheric refraction and many exam numericals.
What is Refraction? Refraction is the change in direction of light when it passes obliquely from one transparent medium to another due to change in speed.
Why Light Bends at an Interface When light enters a medium where its speed changes, one side of the wavefront changes speed earlier than the other side. This changes the direction of the ray.
Speed of Light in Different Media Light travels fastest in vacuum. In a material medium its speed is lower and depends on the refractive index of that medium.
v = c/n
Refraction from rarer medium to denser medium: ray bends towards the normal.
5–8. Refractive Index, Relative Index and Optical Density
Refractive Indexn = c/v
Absolute Refractive Indexn = speed in vacuum / speed in medium
Relative Refractive Indexn₂₁ = n₂/n₁ = v₁/v₂
Optical DensityHigher n means optically denser and lower speed
Absolute Refractive Index The absolute refractive index of a medium is the ratio of speed of light in vacuum to speed of light in that medium.
Relative Refractive Index Relative refractive index compares two media. It tells how many times light is slower or faster in one medium compared with another.
Optical Density Optically denser does not necessarily mean physically denser. It means the medium has higher refractive index for light.
Direction Clue Rarer to denser: bends towards normal. Denser to rarer: bends away from normal.
Optical density comparison through speed of light.
9–10. Snell’s Law and Derivation
Snell’s law gives the exact mathematical relation between angle of incidence and angle of refraction.
n₁ sin i = n₂ sin r
Statement
For a given pair of media and a given colour of light, the ratio of sine of angle of incidence to sine of angle of refraction is constant.
sin i / sin r = constant
Derivation using wavefront idea
Let a wavefront travel from medium 1 to medium 2.
Speed changes from v₁ to v₂ at the boundary.
Using geometry of the wavefront triangles, sin i / sin r = v₁ / v₂.
Since n = c/v, v₁/v₂ = n₂/n₁.
Therefore n₁ sin i = n₂ sin r.
sin i / sin r = v₁ / v₂ = n₂ / n₁
11–18. Plane Surfaces, Glass Slab, Lateral Shift and Apparent Depth
Refraction at Plane Surfaces At a plane boundary, the ray bends according to Snell’s law. The normal is drawn perpendicular to the interface at the point of incidence.
Refraction Through Glass Slab A glass slab has parallel faces, so the emergent ray is parallel to the incident ray but laterally displaced.
Lateral Shift Lateral shift is the perpendicular distance between the original path of incident ray and the emergent ray.
Factors Affecting Lateral Shift Lateral shift increases with slab thickness, angle of incidence and refractive index difference.
Apparent Depth A submerged object appears raised when viewed from air because rays bend away from the normal while emerging.
Apparent Rise Apparent rise is the difference between real depth and apparent depth.
Real Position vs Apparent Position Real position is actual location; apparent position is where backward extensions of refracted rays seem to meet.
Refraction Through Multiple Media Across multiple parallel layers, n sin θ remains constant for the ray path.
d = t sin(i-r)/cos rApparent depth = Real depth / nn₁ sin θ₁ = n₂ sin θ₂ = n₃ sin θ₃
Glass slab lateral shift.
Apparent depth and apparent rise.
Refraction through multiple media.
19. Important Graphs
Refraction graphs are important for identifying refractive index from slope and for understanding variation of lateral shift.
Important graphs in refraction.
20. Complete Formula Sheet
Speed in mediumv = c/n
Absolute indexn = c/v
Relative indexn₂₁ = n₂/n₁ = v₁/v₂
Snell’s lawn₁ sin i = n₂ sin r
Glass slab shiftd = t sin(i-r)/cos r
Apparent depthapparent depth = real depth/n
Apparent risereal depth - apparent depth
Multiple median sin θ = constant
21. One-Page Quick Revision Notes
Core Definitions
Refraction means bending due to change in speed.
Normal is perpendicular to interface.
Optically denser means higher refractive index.
Direction Rules
Rarer to denser: towards normal.
Denser to rarer: away from normal.
Glass slab emergent ray is parallel.
Exam Formulae
n = c/v
n₁ sin i = n₂ sin r
d = t sin(i-r)/cos r
Apparent depth = real depth/n
Numerical Section
Solved numericals from CBSE Class 12, NEET, JEE Main, JEE Advanced, ICSE, IGCSE, IB Physics HL/SL, A-Level and British Curriculum Physics.
CBSE Class 12
CBSE Class 12 Numerical 1. Find speed of light in a medium of refractive index 1.50.
Given: n = 1.50, c = 3 × 10⁸ m/s
n = c/vv = c/n
Substitute: v = 3 × 10⁸ / 1.50
Calculate: v = 2.00e+08 m/s
Final Answer: v = 2.00e+08 m/s
CBSE Class 12 Numerical 2. A ray passes from medium n₁=1.33 to n₂=1.00 at i=30°. Find r.
Given: n₁ = 1.33, n₂ = 1.00, i = 30°
n₁ sin i = n₂ sin rsin r = n₁ sin i / n₂
sin r = (1.33 sin 30°)/1.00
sin r = 0.665
r = 41.68°
Final Answer: r = 41.68°
CBSE Class 12 Numerical 3. A pool is 6 m deep and water has refractive index 1.5. Find apparent depth.
Given: real depth = 6 m, n = 1.5
Apparent depth = Real depth / n
Apparent depth = 6/1.5
Apparent depth = 4.00 m
Final Answer: 4.00 m
CBSE Class 12 Numerical 4. A glass slab of thickness 5 cm has i=40° and r=25°. Find lateral shift.
Given: t = 5 cm, i = 40°, r = 25°
d = t sin(i-r)/cos r
d = 5 sin(15°)/cos(25°)
d = 1.43 cm
Final Answer: d = 1.43 cm
CBSE Class 12 Numerical 5. Find refractive index of medium 2 with respect to medium 1 if n₁=1.33, n₂=1.50.
Given: n₁=1.33, n₂=1.50
n₂₁ = n₂/n₁
n₂₁ = 1.50/1.33
n₂₁ = 1.13
Final Answer: n₂₁ = 1.13
CBSE Class 12 Numerical 6. Find speed of light in a medium of refractive index 1.50.
Given: n = 1.50, c = 3 × 10⁸ m/s
n = c/vv = c/n
Substitute: v = 3 × 10⁸ / 1.50
Calculate: v = 2.00e+08 m/s
Final Answer: v = 2.00e+08 m/s
NEET Physics
NEET Physics Numerical 1. A ray passes from medium n₁=1.00 to n₂=1.33 at i=45°. Find r.
Given: n₁ = 1.00, n₂ = 1.33, i = 45°
n₁ sin i = n₂ sin rsin r = n₁ sin i / n₂
sin r = (1.00 sin 45°)/1.33
sin r = 0.532
r = 32.12°
Final Answer: r = 32.12°
NEET Physics Numerical 2. Find speed of light in a medium of refractive index 1.60.
Given: n = 1.60, c = 3 × 10⁸ m/s
n = c/vv = c/n
Substitute: v = 3 × 10⁸ / 1.60
Calculate: v = 1.88e+08 m/s
Final Answer: v = 1.88e+08 m/s
NEET Physics Numerical 3. A pool is 6 m deep and water has refractive index 1.5. Find apparent depth.
Given: real depth = 6 m, n = 1.5
Apparent depth = Real depth / n
Apparent depth = 6/1.5
Apparent depth = 4.00 m
Final Answer: 4.00 m
NEET Physics Numerical 4. Find refractive index of medium 2 with respect to medium 1 if n₁=1.52, n₂=1.33.
Given: n₁=1.52, n₂=1.33
n₂₁ = n₂/n₁
n₂₁ = 1.33/1.52
n₂₁ = 0.88
Final Answer: n₂₁ = 0.88
NEET Physics Numerical 5. A glass slab of thickness 6 cm has i=45° and r=28°. Find lateral shift.
Given: t = 6 cm, i = 45°, r = 28°
d = t sin(i-r)/cos r
d = 6 sin(17°)/cos(28°)
d = 1.99 cm
Final Answer: d = 1.99 cm
NEET Physics Numerical 6. A ray passes from medium n₁=1.00 to n₂=1.33 at i=45°. Find r.
Given: n₁ = 1.00, n₂ = 1.33, i = 45°
n₁ sin i = n₂ sin rsin r = n₁ sin i / n₂
sin r = (1.00 sin 45°)/1.33
sin r = 0.532
r = 32.12°
Final Answer: r = 32.12°
NEET Physics Numerical 7. Find speed of light in a medium of refractive index 1.60.
Given: n = 1.60, c = 3 × 10⁸ m/s
n = c/vv = c/n
Substitute: v = 3 × 10⁸ / 1.60
Calculate: v = 1.88e+08 m/s
Final Answer: v = 1.88e+08 m/s
JEE Main
JEE Main Numerical 1. A ray passes from medium n₁=1.00 to n₂=1.33 at i=45°. Find r.
Given: n₁ = 1.00, n₂ = 1.33, i = 45°
n₁ sin i = n₂ sin rsin r = n₁ sin i / n₂
sin r = (1.00 sin 45°)/1.33
sin r = 0.532
r = 32.12°
Final Answer: r = 32.12°
JEE Main Numerical 2. A glass slab of thickness 4 cm has i=35° and r=22°. Find lateral shift.
Given: t = 4 cm, i = 35°, r = 22°
d = t sin(i-r)/cos r
d = 4 sin(13°)/cos(22°)
d = 0.97 cm
Final Answer: d = 0.97 cm
JEE Main Numerical 3. Find refractive index of medium 2 with respect to medium 1 if n₁=1.33, n₂=2.42.
Given: n₁=1.33, n₂=2.42
n₂₁ = n₂/n₁
n₂₁ = 2.42/1.33
n₂₁ = 1.82
Final Answer: n₂₁ = 1.82
JEE Main Numerical 4. Find speed of light in a medium of refractive index 2.42.
Given: n = 2.42, c = 3 × 10⁸ m/s
n = c/vv = c/n
Substitute: v = 3 × 10⁸ / 2.42
Calculate: v = 1.24e+08 m/s
Final Answer: v = 1.24e+08 m/s
JEE Main Numerical 5. A pool is 3 m deep and water has refractive index 1.33. Find apparent depth.
Given: real depth = 3 m, n = 1.33
Apparent depth = Real depth / n
Apparent depth = 3/1.33
Apparent depth = 2.26 m
Final Answer: 2.26 m
JEE Main Numerical 6. A ray passes from medium n₁=1.00 to n₂=1.33 at i=45°. Find r.
Given: n₁ = 1.00, n₂ = 1.33, i = 45°
n₁ sin i = n₂ sin rsin r = n₁ sin i / n₂
sin r = (1.00 sin 45°)/1.33
sin r = 0.532
r = 32.12°
Final Answer: r = 32.12°
JEE Main Numerical 7. A glass slab of thickness 4 cm has i=35° and r=22°. Find lateral shift.
Given: t = 4 cm, i = 35°, r = 22°
d = t sin(i-r)/cos r
d = 4 sin(13°)/cos(22°)
d = 0.97 cm
Final Answer: d = 0.97 cm
JEE Advanced
JEE Advanced Numerical 1. A ray passes from medium n₁=1.00 to n₂=1.33 at i=45°. Find r.
Given: n₁ = 1.00, n₂ = 1.33, i = 45°
n₁ sin i = n₂ sin rsin r = n₁ sin i / n₂
sin r = (1.00 sin 45°)/1.33
sin r = 0.532
r = 32.12°
Final Answer: r = 32.12°
JEE Advanced Numerical 2. A glass slab of thickness 4 cm has i=35° and r=22°. Find lateral shift.
Given: t = 4 cm, i = 35°, r = 22°
d = t sin(i-r)/cos r
d = 4 sin(13°)/cos(22°)
d = 0.97 cm
Final Answer: d = 0.97 cm
JEE Advanced Numerical 3. Find refractive index of medium 2 with respect to medium 1 if n₁=1.33, n₂=2.42.
Given: n₁=1.33, n₂=2.42
n₂₁ = n₂/n₁
n₂₁ = 2.42/1.33
n₂₁ = 1.82
Final Answer: n₂₁ = 1.82
JEE Advanced Numerical 4. A pool is 1.8 m deep and water has refractive index 1.33. Find apparent depth.
Given: real depth = 1.8 m, n = 1.33
Apparent depth = Real depth / n
Apparent depth = 1.8/1.33
Apparent depth = 1.35 m
Final Answer: 1.35 m
JEE Advanced Numerical 5. Find speed of light in a medium of refractive index 1.33.
Given: n = 1.33, c = 3 × 10⁸ m/s
n = c/vv = c/n
Substitute: v = 3 × 10⁸ / 1.33
Calculate: v = 2.26e+08 m/s
Final Answer: v = 2.26e+08 m/s
JEE Advanced Numerical 6. A ray passes from medium n₁=1.00 to n₂=1.33 at i=45°. Find r.
Given: n₁ = 1.00, n₂ = 1.33, i = 45°
n₁ sin i = n₂ sin rsin r = n₁ sin i / n₂
sin r = (1.00 sin 45°)/1.33
sin r = 0.532
r = 32.12°
Final Answer: r = 32.12°
ICSE
ICSE Numerical 1. Find speed of light in a medium of refractive index 1.50.
Given: n = 1.50, c = 3 × 10⁸ m/s
n = c/vv = c/n
Substitute: v = 3 × 10⁸ / 1.50
Calculate: v = 2.00e+08 m/s
Final Answer: v = 2.00e+08 m/s
ICSE Numerical 2. A pool is 2 m deep and water has refractive index 1.33. Find apparent depth.
Given: real depth = 2 m, n = 1.33
Apparent depth = Real depth / n
Apparent depth = 2/1.33
Apparent depth = 1.50 m
Final Answer: 1.50 m
ICSE Numerical 3. A ray passes from medium n₁=1.50 to n₂=1.00 at i=30°. Find r.
Given: n₁ = 1.50, n₂ = 1.00, i = 30°
n₁ sin i = n₂ sin rsin r = n₁ sin i / n₂
sin r = (1.50 sin 30°)/1.00
sin r = 0.750
r = 48.59°
Final Answer: r = 48.59°
ICSE Numerical 4. Find refractive index of medium 2 with respect to medium 1 if n₁=1.52, n₂=1.33.
Given: n₁=1.52, n₂=1.33
n₂₁ = n₂/n₁
n₂₁ = 1.33/1.52
n₂₁ = 0.88
Final Answer: n₂₁ = 0.88
IGCSE
IGCSE Numerical 1. A pool is 4.5 m deep and water has refractive index 1.5. Find apparent depth.
Given: real depth = 4.5 m, n = 1.5
Apparent depth = Real depth / n
Apparent depth = 4.5/1.5
Apparent depth = 3.00 m
Final Answer: 3.00 m
IGCSE Numerical 2. Find speed of light in a medium of refractive index 1.60.
Given: n = 1.60, c = 3 × 10⁸ m/s
n = c/vv = c/n
Substitute: v = 3 × 10⁸ / 1.60
Calculate: v = 1.88e+08 m/s
Final Answer: v = 1.88e+08 m/s
IGCSE Numerical 3. A ray passes from medium n₁=1.50 to n₂=1.00 at i=30°. Find r.
Given: n₁ = 1.50, n₂ = 1.00, i = 30°
n₁ sin i = n₂ sin rsin r = n₁ sin i / n₂
sin r = (1.50 sin 30°)/1.00
sin r = 0.750
r = 48.59°
Final Answer: r = 48.59°
IGCSE Numerical 4. A glass slab of thickness 5 cm has i=40° and r=25°. Find lateral shift.
Given: t = 5 cm, i = 40°, r = 25°
d = t sin(i-r)/cos r
d = 5 sin(15°)/cos(25°)
d = 1.43 cm
Final Answer: d = 1.43 cm
IGCSE Numerical 5. A pool is 3 m deep and water has refractive index 1.33. Find apparent depth.
Given: real depth = 3 m, n = 1.33
Apparent depth = Real depth / n
Apparent depth = 3/1.33
Apparent depth = 2.26 m
Final Answer: 2.26 m
IB Physics HL/SL
IB Physics HL/SL Numerical 1. A ray passes from medium n₁=1.00 to n₂=1.33 at i=45°. Find r.
Given: n₁ = 1.00, n₂ = 1.33, i = 45°
n₁ sin i = n₂ sin rsin r = n₁ sin i / n₂
sin r = (1.00 sin 45°)/1.33
sin r = 0.532
r = 32.12°
Final Answer: r = 32.12°
IB Physics HL/SL Numerical 2. Find refractive index of medium 2 with respect to medium 1 if n₁=1.50, n₂=1.00.
Given: n₁=1.50, n₂=1.00
n₂₁ = n₂/n₁
n₂₁ = 1.00/1.50
n₂₁ = 0.67
Final Answer: n₂₁ = 0.67
IB Physics HL/SL Numerical 3. A pool is 6 m deep and water has refractive index 1.5. Find apparent depth.
Given: real depth = 6 m, n = 1.5
Apparent depth = Real depth / n
Apparent depth = 6/1.5
Apparent depth = 4.00 m
Final Answer: 4.00 m
IB Physics HL/SL Numerical 4. A glass slab of thickness 5 cm has i=40° and r=25°. Find lateral shift.
Given: t = 5 cm, i = 40°, r = 25°
d = t sin(i-r)/cos r
d = 5 sin(15°)/cos(25°)
d = 1.43 cm
Final Answer: d = 1.43 cm
IB Physics HL/SL Numerical 5. A ray passes from medium n₁=1.00 to n₂=1.50 at i=30°. Find r.
Given: n₁ = 1.00, n₂ = 1.50, i = 30°
n₁ sin i = n₂ sin rsin r = n₁ sin i / n₂
sin r = (1.00 sin 30°)/1.50
sin r = 0.333
r = 19.47°
Final Answer: r = 19.47°
A-Level / British Curriculum
A-Level / British Curriculum Numerical 1. Find speed of light in a medium of refractive index 1.50.
Given: n = 1.50, c = 3 × 10⁸ m/s
n = c/vv = c/n
Substitute: v = 3 × 10⁸ / 1.50
Calculate: v = 2.00e+08 m/s
Final Answer: v = 2.00e+08 m/s
A-Level / British Curriculum Numerical 2. A ray passes from medium n₁=1.33 to n₂=1.00 at i=30°. Find r.
Given: n₁ = 1.33, n₂ = 1.00, i = 30°
n₁ sin i = n₂ sin rsin r = n₁ sin i / n₂
sin r = (1.33 sin 30°)/1.00
sin r = 0.665
r = 41.68°
Final Answer: r = 41.68°
A-Level / British Curriculum Numerical 3. A pool is 6 m deep and water has refractive index 1.5. Find apparent depth.
Given: real depth = 6 m, n = 1.5
Apparent depth = Real depth / n
Apparent depth = 6/1.5
Apparent depth = 4.00 m
Final Answer: 4.00 m
A-Level / British Curriculum Numerical 4. Find refractive index of medium 2 with respect to medium 1 if n₁=1.52, n₂=1.33.
Given: n₁=1.52, n₂=1.33
n₂₁ = n₂/n₁
n₂₁ = 1.33/1.52
n₂₁ = 0.88
Final Answer: n₂₁ = 0.88
A-Level / British Curriculum Numerical 5. A glass slab of thickness 6 cm has i=45° and r=28°. Find lateral shift.
Given: t = 6 cm, i = 45°, r = 28°
d = t sin(i-r)/cos r
d = 6 sin(17°)/cos(28°)
d = 1.99 cm
Final Answer: d = 1.99 cm
PYQ Section
CBSE PYQs
CBSE PYQs 1. Why does a ray bend towards the normal in glass?
Because light slows down in glass; the part of the wavefront entering first slows earlier, so the ray bends towards the normal.
Answer: Because light slows down in glass; the part of the wavefront entering first slows earlier, so the ray bends towards the normal.
CBSE PYQs 2. If refractive index increases, what happens to speed?
Speed decreases because n = c/v.
Answer: Speed decreases because n = c/v.
CBSE PYQs 3. Why is the emergent ray from a parallel glass slab parallel to the incident ray?
The two slab faces are parallel, so the refraction at the second face reverses the angular deviation of the first face.
Answer: The two slab faces are parallel, so the refraction at the second face reverses the angular deviation of the first face.
CBSE PYQs 4. What does lateral shift depend on?
It depends on slab thickness, refractive index and angle of incidence.
Answer: It depends on slab thickness, refractive index and angle of incidence.
CBSE PYQs 5. Why does a coin in water appear raised?
Rays bend away from the normal while coming from water to air, so backward extensions meet at a shallower point.
Answer: Rays bend away from the normal while coming from water to air, so backward extensions meet at a shallower point.
NEET PYQs
NEET PYQs 1. Why does a ray bend towards the normal in glass?
Because light slows down in glass; the part of the wavefront entering first slows earlier, so the ray bends towards the normal.
Answer: Because light slows down in glass; the part of the wavefront entering first slows earlier, so the ray bends towards the normal.
NEET PYQs 2. If refractive index increases, what happens to speed?
Speed decreases because n = c/v.
Answer: Speed decreases because n = c/v.
NEET PYQs 3. Why is the emergent ray from a parallel glass slab parallel to the incident ray?
The two slab faces are parallel, so the refraction at the second face reverses the angular deviation of the first face.
Answer: The two slab faces are parallel, so the refraction at the second face reverses the angular deviation of the first face.
NEET PYQs 4. What does lateral shift depend on?
It depends on slab thickness, refractive index and angle of incidence.
Answer: It depends on slab thickness, refractive index and angle of incidence.
NEET PYQs 5. Why does a coin in water appear raised?
Rays bend away from the normal while coming from water to air, so backward extensions meet at a shallower point.
Answer: Rays bend away from the normal while coming from water to air, so backward extensions meet at a shallower point.
JEE Main PYQs
JEE Main PYQs 1. Why does a ray bend towards the normal in glass?
Because light slows down in glass; the part of the wavefront entering first slows earlier, so the ray bends towards the normal.
Answer: Because light slows down in glass; the part of the wavefront entering first slows earlier, so the ray bends towards the normal.
JEE Main PYQs 2. If refractive index increases, what happens to speed?
Speed decreases because n = c/v.
Answer: Speed decreases because n = c/v.
JEE Main PYQs 3. Why is the emergent ray from a parallel glass slab parallel to the incident ray?
The two slab faces are parallel, so the refraction at the second face reverses the angular deviation of the first face.
Answer: The two slab faces are parallel, so the refraction at the second face reverses the angular deviation of the first face.
JEE Main PYQs 4. What does lateral shift depend on?
It depends on slab thickness, refractive index and angle of incidence.
Answer: It depends on slab thickness, refractive index and angle of incidence.
JEE Main PYQs 5. Why does a coin in water appear raised?
Rays bend away from the normal while coming from water to air, so backward extensions meet at a shallower point.
Answer: Rays bend away from the normal while coming from water to air, so backward extensions meet at a shallower point.
JEE Advanced PYQs
JEE Advanced PYQs 1. Why does a ray bend towards the normal in glass?
Because light slows down in glass; the part of the wavefront entering first slows earlier, so the ray bends towards the normal.
Answer: Because light slows down in glass; the part of the wavefront entering first slows earlier, so the ray bends towards the normal.
JEE Advanced PYQs 2. If refractive index increases, what happens to speed?
Speed decreases because n = c/v.
Answer: Speed decreases because n = c/v.
JEE Advanced PYQs 3. Why is the emergent ray from a parallel glass slab parallel to the incident ray?
The two slab faces are parallel, so the refraction at the second face reverses the angular deviation of the first face.
Answer: The two slab faces are parallel, so the refraction at the second face reverses the angular deviation of the first face.
JEE Advanced PYQs 4. What does lateral shift depend on?
It depends on slab thickness, refractive index and angle of incidence.
Answer: It depends on slab thickness, refractive index and angle of incidence.
JEE Advanced PYQs 5. Why does a coin in water appear raised?
Rays bend away from the normal while coming from water to air, so backward extensions meet at a shallower point.
Answer: Rays bend away from the normal while coming from water to air, so backward extensions meet at a shallower point.
IB Physics Questions
IB Physics Questions 1. Why does a ray bend towards the normal in glass?
Because light slows down in glass; the part of the wavefront entering first slows earlier, so the ray bends towards the normal.
Answer: Because light slows down in glass; the part of the wavefront entering first slows earlier, so the ray bends towards the normal.
IB Physics Questions 2. If refractive index increases, what happens to speed?
Speed decreases because n = c/v.
Answer: Speed decreases because n = c/v.
IB Physics Questions 3. Why is the emergent ray from a parallel glass slab parallel to the incident ray?
The two slab faces are parallel, so the refraction at the second face reverses the angular deviation of the first face.
Answer: The two slab faces are parallel, so the refraction at the second face reverses the angular deviation of the first face.
IB Physics Questions 4. What does lateral shift depend on?
It depends on slab thickness, refractive index and angle of incidence.
Answer: It depends on slab thickness, refractive index and angle of incidence.
IB Physics Questions 5. Why does a coin in water appear raised?
Rays bend away from the normal while coming from water to air, so backward extensions meet at a shallower point.
Answer: Rays bend away from the normal while coming from water to air, so backward extensions meet at a shallower point.
IGCSE Questions
IGCSE Questions 1. Why does a ray bend towards the normal in glass?
Because light slows down in glass; the part of the wavefront entering first slows earlier, so the ray bends towards the normal.
Answer: Because light slows down in glass; the part of the wavefront entering first slows earlier, so the ray bends towards the normal.
IGCSE Questions 2. If refractive index increases, what happens to speed?
Speed decreases because n = c/v.
Answer: Speed decreases because n = c/v.
IGCSE Questions 3. Why is the emergent ray from a parallel glass slab parallel to the incident ray?
The two slab faces are parallel, so the refraction at the second face reverses the angular deviation of the first face.
Answer: The two slab faces are parallel, so the refraction at the second face reverses the angular deviation of the first face.
IGCSE Questions 4. What does lateral shift depend on?
It depends on slab thickness, refractive index and angle of incidence.
Answer: It depends on slab thickness, refractive index and angle of incidence.
IGCSE Questions 5. Why does a coin in water appear raised?
Rays bend away from the normal while coming from water to air, so backward extensions meet at a shallower point.
Answer: Rays bend away from the normal while coming from water to air, so backward extensions meet at a shallower point.
A-Level Questions
A-Level Questions 1. Why does a ray bend towards the normal in glass?
Because light slows down in glass; the part of the wavefront entering first slows earlier, so the ray bends towards the normal.
Answer: Because light slows down in glass; the part of the wavefront entering first slows earlier, so the ray bends towards the normal.
A-Level Questions 2. If refractive index increases, what happens to speed?
Speed decreases because n = c/v.
Answer: Speed decreases because n = c/v.
A-Level Questions 3. Why is the emergent ray from a parallel glass slab parallel to the incident ray?
The two slab faces are parallel, so the refraction at the second face reverses the angular deviation of the first face.
Answer: The two slab faces are parallel, so the refraction at the second face reverses the angular deviation of the first face.
A-Level Questions 4. What does lateral shift depend on?
It depends on slab thickness, refractive index and angle of incidence.
Answer: It depends on slab thickness, refractive index and angle of incidence.
A-Level Questions 5. Why does a coin in water appear raised?
Rays bend away from the normal while coming from water to air, so backward extensions meet at a shallower point.
Answer: Rays bend away from the normal while coming from water to air, so backward extensions meet at a shallower point.
Case Study Section
Case Study 1: Swimming Pool Apparent Depth
Passage: A swimming pool appears shallower than it really is because light rays from the bottom bend away from the normal when they emerge from water into air.
Application diagram for Swimming Pool Apparent Depth.
MCQ 1. Which phenomenon is mainly involved?
The main phenomenon is refraction of light at a boundary or through layers of changing refractive index.
Answer: Refraction
MCQ 2. Which law is used for angle calculation?
Snell’s law is used.
n₁ sin i = n₂ sin rAnswer: Snell’s law
Assertion-Reason. Assertion: Apparent position can differ from real position. Reason: Refracted rays are extended backwards by the eye.
Both assertion and reason are true, and the reason correctly explains the assertion.
Answer: Both true; reason is correct explanation
Case Study 2: Fish Appearing Higher Than Actual Position
Passage: A fish inside water appears raised to an observer in air. The apparent position is obtained by extending the refracted rays backwards into water.
Application diagram for Fish Appearing Higher Than Actual Position.
MCQ 1. Which phenomenon is mainly involved?
The main phenomenon is refraction of light at a boundary or through layers of changing refractive index.
Answer: Refraction
MCQ 2. Which law is used for angle calculation?
Snell’s law is used.
n₁ sin i = n₂ sin rAnswer: Snell’s law
Assertion-Reason. Assertion: Apparent position can differ from real position. Reason: Refracted rays are extended backwards by the eye.
Both assertion and reason are true, and the reason correctly explains the assertion.
Answer: Both true; reason is correct explanation
Case Study 3: Coin in Water Experiment
Passage: A coin at the bottom of a vessel appears raised when water is poured because of refraction at the water-air surface.
Application diagram for Coin in Water Experiment.
MCQ 1. Which phenomenon is mainly involved?
The main phenomenon is refraction of light at a boundary or through layers of changing refractive index.
Answer: Refraction
MCQ 2. Which law is used for angle calculation?
Snell’s law is used.
n₁ sin i = n₂ sin rAnswer: Snell’s law
Assertion-Reason. Assertion: Apparent position can differ from real position. Reason: Refracted rays are extended backwards by the eye.
Both assertion and reason are true, and the reason correctly explains the assertion.
Answer: Both true; reason is correct explanation
Case Study 4: Glass Slab Applications
Passage: A glass slab produces lateral displacement without changing the final direction of the emergent ray because its opposite faces are parallel.
Application diagram for Glass Slab Applications.
MCQ 1. Which phenomenon is mainly involved?
The main phenomenon is refraction of light at a boundary or through layers of changing refractive index.
Answer: Refraction
MCQ 2. Which law is used for angle calculation?
Snell’s law is used.
n₁ sin i = n₂ sin rAnswer: Snell’s law
Assertion-Reason. Assertion: Apparent position can differ from real position. Reason: Refracted rays are extended backwards by the eye.
Both assertion and reason are true, and the reason correctly explains the assertion.
Answer: Both true; reason is correct explanation
Case Study 5: Optical Fibre Introduction
Passage: Optical fibres guide light using repeated total internal reflection after refraction concepts set the critical-angle condition.
Application diagram for Optical Fibre Introduction.
MCQ 1. Which phenomenon is mainly involved?
The main phenomenon is refraction of light at a boundary or through layers of changing refractive index.
Answer: Refraction
MCQ 2. Which law is used for angle calculation?
Snell’s law is used.
n₁ sin i = n₂ sin rAnswer: Snell’s law
Assertion-Reason. Assertion: Apparent position can differ from real position. Reason: Refracted rays are extended backwards by the eye.
Both assertion and reason are true, and the reason correctly explains the assertion.
Answer: Both true; reason is correct explanation
Case Study 6: Mirage Basics
Passage: A mirage is produced when light travels through layers of air with different refractive indices and bends gradually near hot ground.
Application diagram for Mirage Basics.
MCQ 1. Which phenomenon is mainly involved?
The main phenomenon is refraction of light at a boundary or through layers of changing refractive index.
Answer: Refraction
MCQ 2. Which law is used for angle calculation?
Snell’s law is used.
n₁ sin i = n₂ sin rAnswer: Snell’s law
Assertion-Reason. Assertion: Apparent position can differ from real position. Reason: Refracted rays are extended backwards by the eye.
Both assertion and reason are true, and the reason correctly explains the assertion.
Answer: Both true; reason is correct explanation
Case Study 7: Atmospheric Refraction Basics
Passage: Stars appear slightly shifted because light bends through atmospheric layers of gradually changing refractive index.
Application diagram for Atmospheric Refraction Basics.
MCQ 1. Which phenomenon is mainly involved?
The main phenomenon is refraction of light at a boundary or through layers of changing refractive index.
Answer: Refraction
MCQ 2. Which law is used for angle calculation?
Snell’s law is used.
n₁ sin i = n₂ sin rAnswer: Snell’s law
Assertion-Reason. Assertion: Apparent position can differ from real position. Reason: Refracted rays are extended backwards by the eye.
Both assertion and reason are true, and the reason correctly explains the assertion.
Answer: Both true; reason is correct explanation
Question Bank
Conceptual Questions
Conceptual Questions 1. Why does light bend towards the normal when it enters glass from air?
Light slows down in glass. Due to the change in speed at the boundary, the direction changes towards the normal.
Answer: Because speed decreases in glass.
Conceptual Questions 2. Can refraction occur without bending?
Yes. If light falls normally on the interface, its speed changes but its direction does not change.
Answer: Yes, at normal incidence.
Conceptual Questions 3. Why is glass optically denser than air?
Glass has higher refractive index than air, so light travels slower in glass.
Answer: Higher refractive index.
Conceptual Questions 4. Why does a glass slab shift a ray laterally?
The first surface bends the ray, and the second parallel surface bends it back parallel to original direction, leaving a sideways displacement.
Answer: Two parallel refractions cause lateral displacement.
Conceptual Questions 5. Why does a water tank appear shallower?
Rays from the bottom bend away from the normal while emerging, and their backward extensions meet above the real bottom.
Answer: Due to refraction from water to air.
Conceptual Questions 6. Does refractive index depend on colour?
Yes. Different colours have different speeds in a medium, so refractive index depends on wavelength.
Answer: Yes, due to dispersion.
Assertion-Reason Questions
Assertion-Reason Questions 1. Assertion: A coin in water appears raised. Reason: Refracted rays bend away from normal while going from water to air.
Both statements are true. The reason correctly explains why the coin appears raised.
Answer: Both true; reason is correct explanation.
Assertion-Reason Questions 2. Assertion: Light bends at normal incidence. Reason: Speed changes at the interface.
The reason is true, but the assertion is false. At normal incidence direction does not change.
Answer: Assertion false, reason true.
Assertion-Reason Questions 3. Assertion: Emergent ray from a parallel glass slab is parallel to incident ray. Reason: Opposite faces of slab are parallel.
Both statements are true and the reason correctly explains the assertion.
Answer: Both true; reason is correct explanation.
Assertion-Reason Questions 4. Assertion: Refractive index has no unit. Reason: It is a ratio of two speeds.
Both statements are true and the reason correctly explains the assertion.
Answer: Both true; reason is correct explanation.
Assertion-Reason Questions 5. Assertion: Lateral shift increases with slab thickness. Reason: Longer path inside slab increases separation between incident and emergent directions.
Both statements are true and the reason correctly explains the trend.
Answer: Both true; reason is correct explanation.
Match the Following
Match the Following 1. Match: Snell’s law, absolute refractive index, glass slab, apparent depth, optical density with their correct results.
Correct matching:
Snell’s law → n₁ sin i = n₂ sin r
Absolute refractive index → c/v
Glass slab → Lateral shift
Apparent depth → real depth/n
Optical density → higher refractive index
Answer: 1-b, 2-a, 3-d, 4-c, 5-e
Match the Following 2. Match media air, water, glass, diamond with increasing optical density.
Air has lowest refractive index.
Water has n ≈ 1.33.
Glass has n ≈ 1.5.
Diamond has n ≈ 2.42.
Answer: Air < Water < Glass < Diamond
Match the Following 3. Match formula with concept: n=c/v, d=t sin(i-r)/cos r, n₂₁=n₂/n₁, apparent depth=real depth/n.
Identify each formula by its defining quantity: refractive index, lateral shift, relative refractive index and apparent depth.
HOTS Questions 1. A ray enters a medium but does not bend. Can the refractive index be different?
Yes. If incidence is normal, the ray direction remains unchanged even though speed changes.
Answer: Yes, for normal incidence.
HOTS Questions 2. Two slabs have same thickness but different refractive indices. Which produces more lateral shift?
The slab causing a larger difference between i and r produces more lateral shift. Usually higher refractive index gives larger shift.
Answer: Higher refractive index slab, for same incident angle.
HOTS Questions 3. Why is apparent depth formula approximate?
It assumes near-normal viewing. For large angles, exact ray tracing is required.
Answer: It is for near-normal viewing.
HOTS Questions 4. Can relative refractive index be less than 1?
Yes. If medium 2 is optically rarer than medium 1, n₂₁ = n₂/n₁ is less than 1.
Answer: Yes.
HOTS Questions 5. Why is mirage connected with refraction?
Atmospheric layers have different refractive indices, so light bends gradually.
Answer: Due to refraction in air layers.
Statement-Based Questions
Statement-Based Questions 1. Statement I: Refractive index is dimensionless. Statement II: Speed of light is same in all media.
Statement I is true. Statement II is false because light speed changes in media.
Answer: I true, II false.
Statement-Based Questions 2. Statement I: The emergent ray from glass slab is parallel to incident ray. Statement II: There is no lateral shift.
Statement I is true. Statement II is false; there is lateral shift for oblique incidence.
Answer: I true, II false.
Statement-Based Questions 3. Statement I: Apparent depth is less than real depth for water viewed from air. Statement II: Water is optically denser than air.
Both statements are true.
Answer: Both true.
Statement-Based Questions 4. Statement I: Snell’s law uses angles with normal. Statement II: Angles may be measured from the surface.
Statement I is true. Statement II is false for standard Snell substitution.
Answer: I true, II false.
Multiple Correct Questions
Multiple Correct Questions 1. Select correct statements about refraction.
It occurs due to change in speed.
It follows Snell’s law.
At normal incidence, direction may remain unchanged.
It cannot occur in transparent media is false.
Answer: Statements 1, 2 and 3 are correct.
Multiple Correct Questions 2. Which quantities affect lateral shift in a slab?
Lateral shift depends on thickness, angle of incidence and refractive index of slab.