Goyal Brothers Textbook Solutions: Refraction Of Light

 Page 1


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Refraction of Light 
 
Exercise – 1 
Question 1. 
(a) What do you understand by the term refraction of light? 
(b) How does the light deviate when it travels from ? 
1. a rarer to a denser medium 
2. a denser to a rarer medium? 
Answer: 
(a) Refraction of light : “When light travels from one optical medium to other optical 
medium, it changes its path, this change in path is called refraction of light”. 
(b) (i) Towards the normal, (ii) Away from normal. 
Question 2. 
(a) State the laws of refraction. 
(b) What do you understand by the statement that refractive index of water is 1.33 ? 
Answer: 
(a) Laws of refraction : 
(i) Snell’s law : The ratio between the values of the sine of angle of incidence and the 
sine of angle of refraction for two given optical media is a constant quantity. 
µ = sin i / sin r 
(ii) The incident ray, the refracted ray and the normal lie on the same plane at the point 
of incidence. 
(b) Refractive index of water is 1.33 means that speed of light in air is 1.33 times faster 
than in water. 
Question 3. 
Describe how will you verify the laws of refraction ? 
Answer: 
Experiment To Verify The Laws : 
Fix a white sheet of paper on a drawing board. Place a rectangular glass slab in the 
middle of paper and draw its boundry with a pencil. The block is removed and on the 
boundry line KL a point O is chosen and a normal is drawn. 
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Page 2


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Refraction of Light 
 
Exercise – 1 
Question 1. 
(a) What do you understand by the term refraction of light? 
(b) How does the light deviate when it travels from ? 
1. a rarer to a denser medium 
2. a denser to a rarer medium? 
Answer: 
(a) Refraction of light : “When light travels from one optical medium to other optical 
medium, it changes its path, this change in path is called refraction of light”. 
(b) (i) Towards the normal, (ii) Away from normal. 
Question 2. 
(a) State the laws of refraction. 
(b) What do you understand by the statement that refractive index of water is 1.33 ? 
Answer: 
(a) Laws of refraction : 
(i) Snell’s law : The ratio between the values of the sine of angle of incidence and the 
sine of angle of refraction for two given optical media is a constant quantity. 
µ = sin i / sin r 
(ii) The incident ray, the refracted ray and the normal lie on the same plane at the point 
of incidence. 
(b) Refractive index of water is 1.33 means that speed of light in air is 1.33 times faster 
than in water. 
Question 3. 
Describe how will you verify the laws of refraction ? 
Answer: 
Experiment To Verify The Laws : 
Fix a white sheet of paper on a drawing board. Place a rectangular glass slab in the 
middle of paper and draw its boundry with a pencil. The block is removed and on the 
boundry line KL a point O is chosen and a normal is drawn. 
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Through O a line OA at an angle i (say 60°) with the normal is drawn. The block is 
replaced on its boundry line. Two pins a and b are fixed vertically on the board about 10 
cm apart on the line AO. Looking from the other side NM of the slab two more pins c 
and d are fixed such that legs of pins c and d and images of pins a and b seen through 
glass are in a straight line. 
Pins are removed and pin pricks are marked with pencil. 
Slab is removed and marks c and d are joined by line BC to meet the boundry at B. OB is 
joined. 
AO represents INCIDENT RAY 
BC represents EMERGENT RAY 
OB represents REFRACTED RAY 
? AON represents ANGLE OF INCIDENCE i 
?BOM represents ANGLE OF REFRACTION r 
with O as centre and suitable radius draw a circle intersecting AO at X and OB at Y. 
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Refraction of Light 
 
Exercise – 1 
Question 1. 
(a) What do you understand by the term refraction of light? 
(b) How does the light deviate when it travels from ? 
1. a rarer to a denser medium 
2. a denser to a rarer medium? 
Answer: 
(a) Refraction of light : “When light travels from one optical medium to other optical 
medium, it changes its path, this change in path is called refraction of light”. 
(b) (i) Towards the normal, (ii) Away from normal. 
Question 2. 
(a) State the laws of refraction. 
(b) What do you understand by the statement that refractive index of water is 1.33 ? 
Answer: 
(a) Laws of refraction : 
(i) Snell’s law : The ratio between the values of the sine of angle of incidence and the 
sine of angle of refraction for two given optical media is a constant quantity. 
µ = sin i / sin r 
(ii) The incident ray, the refracted ray and the normal lie on the same plane at the point 
of incidence. 
(b) Refractive index of water is 1.33 means that speed of light in air is 1.33 times faster 
than in water. 
Question 3. 
Describe how will you verify the laws of refraction ? 
Answer: 
Experiment To Verify The Laws : 
Fix a white sheet of paper on a drawing board. Place a rectangular glass slab in the 
middle of paper and draw its boundry with a pencil. The block is removed and on the 
boundry line KL a point O is chosen and a normal is drawn. 
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Through O a line OA at an angle i (say 60°) with the normal is drawn. The block is 
replaced on its boundry line. Two pins a and b are fixed vertically on the board about 10 
cm apart on the line AO. Looking from the other side NM of the slab two more pins c 
and d are fixed such that legs of pins c and d and images of pins a and b seen through 
glass are in a straight line. 
Pins are removed and pin pricks are marked with pencil. 
Slab is removed and marks c and d are joined by line BC to meet the boundry at B. OB is 
joined. 
AO represents INCIDENT RAY 
BC represents EMERGENT RAY 
OB represents REFRACTED RAY 
? AON represents ANGLE OF INCIDENCE i 
?BOM represents ANGLE OF REFRACTION r 
with O as centre and suitable radius draw a circle intersecting AO at X and OB at Y. 
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Draw normals XY and X’ Y’. Measure XY and X’ Y’. 
 
Question 4. 
(a) What do you understand by the term lateral displacement ? 
(b) State three factors which determine lateral displacement ? 
Answer: 
(a) Lateral Displacement : “The perpendicular shift in the path of the incident ray while 
emerging out of an optical slab is called Lateral Displacement.” 
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Refraction of Light 
 
Exercise – 1 
Question 1. 
(a) What do you understand by the term refraction of light? 
(b) How does the light deviate when it travels from ? 
1. a rarer to a denser medium 
2. a denser to a rarer medium? 
Answer: 
(a) Refraction of light : “When light travels from one optical medium to other optical 
medium, it changes its path, this change in path is called refraction of light”. 
(b) (i) Towards the normal, (ii) Away from normal. 
Question 2. 
(a) State the laws of refraction. 
(b) What do you understand by the statement that refractive index of water is 1.33 ? 
Answer: 
(a) Laws of refraction : 
(i) Snell’s law : The ratio between the values of the sine of angle of incidence and the 
sine of angle of refraction for two given optical media is a constant quantity. 
µ = sin i / sin r 
(ii) The incident ray, the refracted ray and the normal lie on the same plane at the point 
of incidence. 
(b) Refractive index of water is 1.33 means that speed of light in air is 1.33 times faster 
than in water. 
Question 3. 
Describe how will you verify the laws of refraction ? 
Answer: 
Experiment To Verify The Laws : 
Fix a white sheet of paper on a drawing board. Place a rectangular glass slab in the 
middle of paper and draw its boundry with a pencil. The block is removed and on the 
boundry line KL a point O is chosen and a normal is drawn. 
Downloaded from https://www.ncertbooksolutions.com/
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Through O a line OA at an angle i (say 60°) with the normal is drawn. The block is 
replaced on its boundry line. Two pins a and b are fixed vertically on the board about 10 
cm apart on the line AO. Looking from the other side NM of the slab two more pins c 
and d are fixed such that legs of pins c and d and images of pins a and b seen through 
glass are in a straight line. 
Pins are removed and pin pricks are marked with pencil. 
Slab is removed and marks c and d are joined by line BC to meet the boundry at B. OB is 
joined. 
AO represents INCIDENT RAY 
BC represents EMERGENT RAY 
OB represents REFRACTED RAY 
? AON represents ANGLE OF INCIDENCE i 
?BOM represents ANGLE OF REFRACTION r 
with O as centre and suitable radius draw a circle intersecting AO at X and OB at Y. 
Downloaded from https://www.ncertbooksolutions.com/
Downloaded from https://www.ncertbooksolutions.com/
https://www.ncertbooksolutions.com
Draw normals XY and X’ Y’. Measure XY and X’ Y’. 
 
Question 4. 
(a) What do you understand by the term lateral displacement ? 
(b) State three factors which determine lateral displacement ? 
Answer: 
(a) Lateral Displacement : “The perpendicular shift in the path of the incident ray while 
emerging out of an optical slab is called Lateral Displacement.” 
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(b) Factors : 
1. Angle of incidence 
2. Thickness of optical slab 
3. Refractive index of opitcal material. 
4. Wavelength of light. 
Question 5. 
By drawing neat diagrams explain : 
(a) Why does a stick immersed obliquely in water, appear bent and short ? 
(b) Why does a stamp placed under a glass block, appear raised? 
(c) Why is twilight formed, before sunrise or sunset ? 
(d) Why do stars twinkle, but not the planets ? 
(e) Why do the faces of people sitting around a camp fire appear to shimmer ? 
(f) Why does a tank filled with water and seen from above appear shallow ? 
(g) Why does a fisherman aim his spear at the tail of a fish during spear fishing. 
(h) Why is more than one image formed in a thick glass mirror? 
(i) Why does the sun appear bigger during sunrise or sunset? 
Answer: 
(a) The stick appears to be bent and raised up in place of BA as BA’ due to refraction of 
light on passing from denser medium (water) to rarer medium (air) 
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Page 5


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Refraction of Light 
 
Exercise – 1 
Question 1. 
(a) What do you understand by the term refraction of light? 
(b) How does the light deviate when it travels from ? 
1. a rarer to a denser medium 
2. a denser to a rarer medium? 
Answer: 
(a) Refraction of light : “When light travels from one optical medium to other optical 
medium, it changes its path, this change in path is called refraction of light”. 
(b) (i) Towards the normal, (ii) Away from normal. 
Question 2. 
(a) State the laws of refraction. 
(b) What do you understand by the statement that refractive index of water is 1.33 ? 
Answer: 
(a) Laws of refraction : 
(i) Snell’s law : The ratio between the values of the sine of angle of incidence and the 
sine of angle of refraction for two given optical media is a constant quantity. 
µ = sin i / sin r 
(ii) The incident ray, the refracted ray and the normal lie on the same plane at the point 
of incidence. 
(b) Refractive index of water is 1.33 means that speed of light in air is 1.33 times faster 
than in water. 
Question 3. 
Describe how will you verify the laws of refraction ? 
Answer: 
Experiment To Verify The Laws : 
Fix a white sheet of paper on a drawing board. Place a rectangular glass slab in the 
middle of paper and draw its boundry with a pencil. The block is removed and on the 
boundry line KL a point O is chosen and a normal is drawn. 
Downloaded from https://www.ncertbooksolutions.com/
Downloaded from https://www.ncertbooksolutions.com/
https://www.ncertbooksolutions.com
 
Through O a line OA at an angle i (say 60°) with the normal is drawn. The block is 
replaced on its boundry line. Two pins a and b are fixed vertically on the board about 10 
cm apart on the line AO. Looking from the other side NM of the slab two more pins c 
and d are fixed such that legs of pins c and d and images of pins a and b seen through 
glass are in a straight line. 
Pins are removed and pin pricks are marked with pencil. 
Slab is removed and marks c and d are joined by line BC to meet the boundry at B. OB is 
joined. 
AO represents INCIDENT RAY 
BC represents EMERGENT RAY 
OB represents REFRACTED RAY 
? AON represents ANGLE OF INCIDENCE i 
?BOM represents ANGLE OF REFRACTION r 
with O as centre and suitable radius draw a circle intersecting AO at X and OB at Y. 
Downloaded from https://www.ncertbooksolutions.com/
Downloaded from https://www.ncertbooksolutions.com/
https://www.ncertbooksolutions.com
Draw normals XY and X’ Y’. Measure XY and X’ Y’. 
 
Question 4. 
(a) What do you understand by the term lateral displacement ? 
(b) State three factors which determine lateral displacement ? 
Answer: 
(a) Lateral Displacement : “The perpendicular shift in the path of the incident ray while 
emerging out of an optical slab is called Lateral Displacement.” 
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(b) Factors : 
1. Angle of incidence 
2. Thickness of optical slab 
3. Refractive index of opitcal material. 
4. Wavelength of light. 
Question 5. 
By drawing neat diagrams explain : 
(a) Why does a stick immersed obliquely in water, appear bent and short ? 
(b) Why does a stamp placed under a glass block, appear raised? 
(c) Why is twilight formed, before sunrise or sunset ? 
(d) Why do stars twinkle, but not the planets ? 
(e) Why do the faces of people sitting around a camp fire appear to shimmer ? 
(f) Why does a tank filled with water and seen from above appear shallow ? 
(g) Why does a fisherman aim his spear at the tail of a fish during spear fishing. 
(h) Why is more than one image formed in a thick glass mirror? 
(i) Why does the sun appear bigger during sunrise or sunset? 
Answer: 
(a) The stick appears to be bent and raised up in place of BA as BA’ due to refraction of 
light on passing from denser medium (water) to rarer medium (air) 
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(b) A stamp placed under a glass block appears raised because of refraction of light as 
light travels from denser to rarer medium, also due to R.I of glass observed depth is less 
than real depth. 
(c) Twilight is formed, before the sunrise or sun set due to refraction of sun light as 
even when the sun is below the horizon its rays manage to reach the earth due to 
refraction. 
(d) Stars twinkle : because of refraction of light as light passes through different layers 
of air of different densities mix, changes the apparent position of star. When the star is 
with in the line of sight it is visible but when it falls out of the line of sight, it is no longer 
visible. The collective effect of the above changes shift the apparent position of the star 
and it appears to twinkle. 
Planets do not twinkle : Planets are very close to us compared to the stars. Their 
apparent of position also changes with change of density of different layers of the 
atmosphere. However the size of their apparent image is still fairly large and seldom fall 
out side the line of sight. Hence they do not appear to twinkle. 
(e) The rays of light reflected from the face of the person, sitting opposite to you, on 
passing through hot air (produced by burning wood), get refracted. Since the hot air is 
rapidly moving and its density is continuously changing, therefore the path of the 
refracted rays also changes. This gives rise to the shimmering effect and person 
appears to shimmer. 
(f) Due to refraction of light when light travels from optically denser medium (water) to 
optically rarer medium (air) observed depth is less than real depth, and the water tank 
appears to be shallow. 
(g) Due to refraction of light when light travels from denser medium (water) to rarer 
medium (air). The real depth is more than apparent depth. 
(h) In a thick glass mirror, light partially gets reflected (4%) and remaining 96% passes 
into the glass plate suffers refraction again and again and multiple images are formed. 
(i) Sun appears to be bigger during sun set or sun rise as “The rays of light travel 
through maximum length of atmosphere” due to refraction, the image of sun is very 
much closer to the eye. Thus, it appears bigger. 
Question 6. 
What is refractive index of a material ? How is it related to (a) real and apparent depth 
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