rationalisation of sqre roots by using Identity 9th cbse

amazing facts about light 10th cbse

Top 45 Amazing Facts About Light | Amazing Facts 4U

1. Light energy is the only energy visible to the human eye. Light rays have different colors due to differing wavelengths.
2. Light energy is made of electromagnetic radiation. A light wave consists of energy in the form of electric and magnetic fields. The fields vibrate at right angles to the direction of movement of the wave, and at right angles to each other.
3. Red light has the longest wavelength while violet light has the shortest wavelength. Scientists study the properties and behaviors of light in a branch of physics known as optics.
4. Obviously, the biggest source of light energy is Sun comes from the Sun. It transfers an incredible amount of energy to our planet in spite of being millions of miles away.
5. Without the light energy from the Sun, humans and all other living creatures can’t survive. Plants absorb light energy to make food. Without sunlight, plants would not survive. Without light energy from Sun, our planet would be too cold for us to continue living!
6. The wavelengths of the light that most people can see ranges from 400 to 700 billionths of a meter. Infrared and Ultra Violet rays are found just beyond visible spectrum.
7. The speed of light is approximately 300,000 kilometers per second which is faster than the speed of anything else! The speed of light changes when travelling through different objects.
8. Unlike sound waves or water waves, light does not need any matter or material to carry its energy along. Thus, light can travel through a vacuum.
9. Light takes 1.25 seconds to get from the Earth to the Moon and about 8 minutes from the Sun to earth. Really long distances can be measured in light year which is the distance that light can travel in a year.
10. A ‘jiffy’ is an actual unit of time. It is the time it takes for light to travel one cm in a vacuum, which is about 33.3564 picoseconds.
11. Light energy actually travels an infinite distance and the distance it extends does not depend on the brightness of the bulb. Our eyes can only see light of certain brightness; therefore, can’t see diminished brightness giving the impression that light has stopped.
12. Amazingly light energy is always moving and can therefore not be stored.
13. Humans and animals would be unable to see anything without light energy. It’s because of light that we have the sense of sight.
14. The cornea on the front of the eye serves to focus the light entering the eye. It is further focused through the lens of the eye in order to form an image on the retina. The pupil of the eye is not a black object or spot on the surface of the eye. It is an opening in the center of the iris. It helps control the amount of light entering the eye.
15. Besides sunlight, light is emitted by hot objects such as light bulbs, and Lasers. A laser produces an incredibly powerful, concentrated form of light. This is the result of light waves bouncing back and forth between two mirrors to build up energy before being released as a narrow powerful beam which can travel long distance without losing quality.
16. Amazingly space is dark because light is only visible when it has an object from which it can bounce off to be visible.
17. Light energy travels in a straight line passing through transparent materials like glass and bouncing off other materials which are not transparent. The light rays can also bend with change of medium which is known as refraction.
18. Light waves travel out from their source in straight lines called rays. Rays do not curve around corners, so when they hit an opaque object, they are blocked from reaching the other side of that object. Shadow is the area where light is blocked.
19. The light energy from the sun provides our Earth with heat and controls its temperatures.
20. If our skin is over-exposed to sunlight it can burn and chronic exposure can lead to skin cancer. It can also damage our eyes if we look directly at the Sun.
21. Light energy reflects off surfaces. Moonlight is not produced directly by the moon. Actually, the Sun shines on the moon and the light is reflected back to Earth!
22. Light energy can be converted into other types of energy such as solar and chemical energy. During photosynthesis, plants use light energy to create chemical energy wherein carbon dioxide is converted to food.
23. Amazingly every second around 100 lightning bolts strike the Earth. In fact, lightning kills 1000 people every year in the world.
24. Red, green and blue (RGB) are the primary colors of light. Mixing them in various ways will make all other colors, including white.
25. When sunlight is intercepted by a drop of water in the atmosphere, some of the light refracts into the drop, reflects from the drop’s inner surface, and then refracts out of the drop. The first refraction separates the sunlight into its component colors, and the second refraction increases the separation. The resultant refraction in billions of drops in the clouds result in a rainbow.
26. In fact, there are millions of colours in a rainbow. We classify them into 7 main groups of colours that our eyes can see.
27. Isaac Newton observed for the first time that a thin beam of sunlight hitting a glass prism on an angle creates a band of visible rainbow colours because different colours travel through glass at different speeds, causing them to refract at different angles and separate from each other.
28. Mediums are given a refractive index to describe by how much they slow the movement of light. Glass has a refractive index of 1.5, meaning that lights travels through it at around 1/1.5 speed (200,000 kilometres per second). The refractive index of water is 1.3 while the refractive index of air is 1.0003.
29. Refraction can make things look closer than they really are. The difference in speed between light traveling through water and through air means that, from the surface, a 4-meter pool appears to be just 3-meter deep.
30. More than half of the visible light spectrum is absorbed within 3 feet of the ocean’s surface; at a depth of 10 meters, less than 20% of the light that entered at the surface is still visible; by 100 meters, this percentage drops to 0.5%.
31. When light energy passes through a prism, the colors that make up white light are separated and made visible to the human eye (VIBGYOR).
32. The light bulb was invented in 1879 by Thomas Alva Edison.
33. Amazingly when you turn on a light bulb only 10 % of the electricity used is turned into light, the other 90 % is wasted as heat.
34. Low energy light bulbs last on average up to 12 times longer than traditional fluorescent bulbs.
35. UV lights having shortest wave lengths are often used by forensic scientists to see details that are not seen by the naked eye. Although humans cannot see UV light, some insects and animals have the ability to see it
36. About 20% of the human population is estimated to be affected by a so-called “photic sneeze reflex,” a heritable condition that results in sneezing when the person is exposed to bright light.
37. The light from the dazzling northern lights is the result of solar wind which during solar flares reach Earth’s atmosphere interacting with particles of oxygen atoms, causing them to emit stunning green lights.
38. The Hubble telescope has detected the existence of countless galaxies receding from our point in space at speeds in excess of the speed of light. This massive expansion also means that there are some galaxies whose light we’ll never see.
39. In fact, at depths of over 1000 meters, a region of the ocean dubbed the “aphotic zone” there is no detectable light whatsoever. As a result, the largest source of light in the Earth’s oceans actually emanates from animals residing in its depths which are bio luminescent (About 80 to 90%).
40. All living creatures including humans produce some amount of light as a result of metabolic biochemical reactions. This light is thousand times weaker than what human eye can perceive.
41. All humans have the ability to see ultraviolet light, but it is passively filtered out by the eye’s lens. Patients who undergo surgery to remove the lens can detect ultraviolet light.
42. Peacock feathers are actually brown, but have microscopic structures that interfere with light that make the bright iridescence.
43. In 1999, Harvard physicist Lene Hau was able to slow down light to 17 meters per second and in 2001, was able to stop light completely.
44. Amazingly there is a deep-sea fish named Stoplight Loosejaw that takes advantage of the fact that fish can’t see red light, and illuminates its prey with a beam of red bio luminescence so it can hunt with an effectively invisible beam of light.
45. According to English law, the “Right to light” states that the owner of a building with windows who has received natural daylight for 20 years or more is entitled to forbid any construction or other obstruction that would deprive him or her of that illumination.

glass slab activity quewtions

CBSE Class 10 Physics Lab Manual Questions

Question 1:
Why are incident and emergent rays parallel to each other in case of a rectangular glass slab?
Answer:
The incident ray and the emergent ray are parallel to each other in case of a rectangular glass slab because the angle of incidence and angle of emergence are same at opposite parallel surfaces of slab.

Question 2:
Why does a ray of light bend towards the normal when it enters from air in a glass slab and bends away from the normal when it emerges out into air?
Answer:
When light enters from air to glass slab its speed decreases and bends towards the normal. But when the light travels from glass slab to air its speed increases and bends away from the normal.

Question 3:
Draw the path of a ray of light when it enters perpendicular to the surface of a glass slab.
Answer:
The path of light when it enters perpendicular to the surface of glass slab would be a straight line passing through
the glass slab.

Question 4:
While tracing the path of ray of light through a glass slab, the angle of incidence is generally taken between 30° and 60°. Explain the reason on the basis of your performing this experiment for different angles of incidence.
Answer:
This is because for any angle greater or smaller than this range (30 degrees to 60 degrees) the emergent ray would not appear on the opposite side of the slab.

Question 5:
How does the lateral displacement of emergent ray depend on the width of the glass slab and angle of incidence?
Answer:
The lateral displacement is directly proportional to the thickness of the glass slab and the angle of incidence.

Lab Manual Class 10 Science Multiple Choice Questions

Questions based on Procedural and Manipulative Skills
Question 1:
In the experiment to trace the path of a ray of light through a rectangular glass slab using pins P1, P2, P3 and P4, four students did the following:
A. Looked at heads of P1 and P2, while placing P3, and heads of P1, P2 and P3 while placing P4 .
B. Looked at feet of P1, P2 while placing P3 and feet of P1, P2 and P3 while placing P4 .
C. Looked at heads of P1 and P2, while placing P3 and feet of all the pins while placing P4.
D. Looked at feet of P1 and P2 while placing P3 and heads of all the pins while placing P4.
The correct procedure is that of student
(a) A               (b) B               (c) C                 (d) D.
Answer:
(b)
Explanation:
It is the correct procedure.

Question 2:
Lateral displacement depends on:
(a) angle of incidence
(b) angle of refraction
(c) thickness of glass slab
(d) angle of emergence.
Answer:
(c)
Explanation:
The bending of light depends on the medium.

Question 3:
If the angle of incidence is 0°, the angle of refraction in the same medium will be:
(a) 90°              (b) 0°
(c) 180°            (d) less than 0°.
Answer:
(b)
Explanation:
As per formula.

Question 4:
The relation between ∠i, ∠r and n (refractive index) is:
(a) n = sin i/sin r
(b) n = sin r/sin i
(c) n sin i = n sin r
(d) sin i = n sin r
Answer:
(a)
Explanation:
Formula of refraction.

Question 5:
A student suggested the following ‘guidelines’ to his friend for doing the experiment on tracing the path of a ray of light passing through rectangular glass slab for three different angles of incidence.
A. Draw the ‘outline’ of the glass slab at three positions on the drawing sheet.
B. Draw ‘normals’ on the top side of these ‘outlines’ near their left end.
C. Draw the incident rays on the three ‘outlines’ in the directions making angles of 30°, 45°, 60° with the normals drawn.
D. Fix two pins vertically on each of these incident rays at two points nearly 1 cm apart.
E. Look for the images of the ‘heads’ of these pins while fixing two pins from the other side, to get the refracted rays.
When he showed these ‘guidelines’ to his teacher, the teacher corrected and modified the ‘guidelines’ labelled as: (The information was insufficient or incorrect)
(a) B, C, E           (b) B, D, E
(c) B, C, D           (d) C, D, E.
Answer:
(b)
Explanation:
It is the correct option.

Question 6:
The incident ray and the emergent ray in the glass slab are:
(a) always parallel               (b) converging always
(c) sometimes parallel        (d) sometimes diverging.
Answer:
(a)
Explanation:
These two rays do not meet.

Question 7:
The speed of light is maximum in:
(a) oil               (b) water
(c) glass           (d) air.
Answer:
(d)
Explanation:
The speed of light is higher in a rarer medium than a denser medium.

Question 8:
In refraction of light, the angle of incidence and angle of refraction is same when:
(a) ∠i = 90°            (b) ∠i = 180°
(c) ∠i = 0°               (d) none of these
Answer:
(c)
Explanation:
As per the formula and law.

Question 9:
When ray of light travels from air to glass slab its wavelength:
(a) increases
(b) no change
(c) decreases
(d) depends on glass slab thickness.
Answer:
(c)
Explanation:
Speed decreases hence wavelength decreases.

Question 10:
The bending of light when it passes from one medium to the other is called:
(a) dispersion          (b) diffraction
(c) refraction            (d) reflection.
Answer:
(c)
Explanation:
Refraction is changing the paths of light when it passes through different media.

Question 11:
In an experiment to trace the path of a ray of light passing through a rectangular glass slab, four students tabulated their observation as given below

The student most likely to have done the experiment properly is
(a) A               (b) B              (c) C              (d) D
Answer:
(a)
Explanation:
We must not only have the angle of emergence
(nearly) equal to the angle of incidence but also have an idea of the magnitude of the angle of refraction (for a glass slab) for the three most often used values (30°, 45°, 60°) of the angle of incidence.

Questions based on Observational Skills
Question 12:
A student traces the path of a ray of light passing through a rectangular glass slab. For measuring the angle of incidence, he must position the protractor in the manner shown in the figure:

(a) A          (b) B            (c) C               (d) D
Answer:
(b)
Explanation:
The angle is measured between the normal ray and the incident ray.

Question 13:
In an experiment on tracing the path of a ray of light passing through a rectangular glass slab, the correct setting of the protractor (D) for measuring the angle of incidence ∠i and the angle of emergence ∠e corresponds, respectively to diagram is:

(a) K and M          (b) K and N
(c) L and M          (d) L and N.
Answer:
(a)
Explanation:
The angles need to be measured from the normal ray.

Question 14:
Four students traced the path of a ray of light from glass to air as shown below. The correct path of refracted ray is:

Answer:
(b)
Explanation:
Denser to rarer and away from the normal.

Question 15:
When light passes from rarer medium to denser medium, the light will bend:
(a) towards the normal
(b) away from normal
(c) depends on thickness of glass slab
(d) depends on the angle of incidence.
Answer:
(a)
Explanation:
(RDTN) The ray from rarer to denser medium bends towards the normal.

Question 16:
In these diagrams, the angle of refraction r is correctly marked in which diagram?

(a) I               (b) II                (c) III                (d) IV
Answer:
(d)
Explanation:
Angle r is between the normal and the refracted ray.

Question 17:
A student traces the path of a ray of white light through a rectangular glass slab and marks the angles of incidence (∠i), refraction (∠r) and emergence (∠e) as shown in the figure. Which angle or angles has he NOT marked correctly?
(a) ∠i only               (b) ∠i and ∠r
(c) ∠i and ∠e           (d) ∠r and ∠e
Answer:
(c)
Explanation:
Angle should be between the normal ray and the incident ray, the normal and the emergent rays.

Question 18:
Four students showed the following traces of the path of a ray of light passing through a rectangular glass slab.

The trace most likely to be correct is that of student:
(a) I                (b) II                (c) III                 (d) IV
Answer:
(c)
Explanation:
The shift of I and E rays is appropriate.

Question 19:
Select from the following the best set-up for tracing the path of a ray of light through a rectangular glass slab:

(a) I                (b) II                 (c) III                  (d) IV
Answer:
(a)
Explanation:
The angle of incidence and distance between two points is appropriate.

Questions based on Reporting and Interpretation Skills
Question 20:
In an experiment to trace the path of a ray of light passing through a rectangular glass slab, four students tabulated their observations as given below:

StudentsABCD∠i30°30°30°30°∠r18°20°17°21.5°∠e32°32.5°30°34.5°

Which student performed the experiment correctly?
(a) A             (b) B               (c) C                (d) D
Answer:
(c)
Explanation:
∠i and ∠e are same and angle r is less than angle i.

Question 21:
A student does the experiment on tracing the path of a ray of light through a rectangular glass slab for different angles of incidence. He can get a correct measure of the angle of incidence and the angle of emergence by following the labelling indicated in figure:

(a) A               (b) B                (c) C                  (d) D
Answer:
(d)
Explanation:
The angle is measured between the normal ray and the incident ray.

Question 22:
A student performs the experiment on tracing the path of a ray of light passing through a rectangular glass slab for different angles of incidence. He measures the angle of incidence ∠i, angle of refraction ∠r and angle of emergence ∠e for all his observations. He would find that in all cases
(a) ∠i is more than ∠r but (nearly) equal to ∠e
(b) ∠i is less than ∠r but (nearly) equal to ∠e
(c) ∠i is more than ∠e but (nearly) equal to ∠r
(d) ∠i is less than ∠e but (nearly) equal to ∠r
Answer:
(a)
Explanation:
∠i and ∠e are same and angle r is less than angle i.

Question 23:
The two dots Pt and P2 shown in each of the following diagrams I, II, III and IV denote the position of two pins in respect of distance and direction for performing an experiment on tracking the path of a ray of light passing through a rectangular glass slab. In which one of the four cases, one is likely to get the best result?

(a) I             (b) II                 (c) III                 (d) IV
Answer:
(c)
Explanation:
Dots P and P, should be on incident ray making an angle of 30 to 60 degree with the normal.

Question 24:
Out of the four set-ups shown for carrying out the experiment to trace the path of a ray of light through a rectangular glass slab, the best set-up is

(a) A              (b) B                 (c) C                  (d) D
Answer:
(b)
Explanation:
Dots should be on incident ray making an angle of 30 to 60 degree with the normal.

Question 25:
In an experiment to trace the path of a ray of light passing through a rectangular glass slab, the correct measurement of angles of incidence (i), refraction (r) and emergence (e) is shown in the diagrams.

(a) A              (b) B                (c) C                (d) D.
Answer:
(a)
Explanation:
∠i = ∠e , ∠i > ∠r.

Question 26:
The path of a ray of light passing through a rectangular glass slab was traced and angles measured. Which one out of the following is the correct representation of an angle of incidence (i), angle of refraction (r) and angle of emergence (e) as shown in the diagrams:

(a) I            (b) II                 (c) III               (d) IV
Answer:
(d)
Explanation:
The angle is always formed between the normal and the ray (incident/refracted/emergent).

Question 27:
An experiment to trace the path of a ray of light through a glass was performed by four students A, B, C and D. They reported the following measurements of angle of incidence i, angle of refraction r and angle of emergence e.

Student∠i∠r∠eA30°30°20°B40°50°40°C40°30°48°D40°30°40°

student performed the experiment correctly?
(a) A           (b) B             (c) C             (d) D
Answer:
(d)
Explanation:
angle i = angle e, angle i > angle r.

Question 28:
The correct path of a ray of light passing from air to kerosene oil and from kerosene oil to water is

(a) A               (b) B              (c) C               (d) D
Answer:
(a)
Explanation:
Ray from rarer to denser medium is towards the normal and from denser to rarer is away from the normal.

Question 29:
A ray of light enters air from water and experiences refraction, then
(a) ∠i = ∠r               (b) ∠i < ∠r
(c) ∠i > ∠r               (d) ∠i / ∠r = 0°.
Answer:
(b)
Explanation:
Light is passing from denser to rarer medium.

Question 30:
Four students A, B, C and D traced the paths of incident ray and the emergent ray by fixing pins P and Q for incident ray and pins R and S for emergent ray for a ray of light passing through a glass slab.

The correct emergent ray was traced by the student:
(a) A              (b) B              (c) C                (d) D
Answer:
(b)
Explanation:
The bending of light is correct (DRAN) and (RDTN).

Question 31:
A ray of light is incident normally, the angle of incidence is:
(a) 90°              (b) 60°             (c) 180°                 (d) 0°.
Answer:
(d)
Explanation:
No angle is made as the incident and the normal rays are straight and same lines.

Question 32:
A student traces the path of a ray of light through a rectangular glass slab for four different angles of incidence. He very cautiously measures the angle i, angle r and the angle e. On analyzing his measurements, he is likely to draw the following conclusion:
(a) ∠i = ∠e < ∠r                (b) ∠i  >  ∠r  > ∠e
(c) ∠i = ∠ r < ∠e               (d) ∠i = ∠e > ∠r
Answer:
(d)
Explanation:
Angle i = angle e, but angle of refraction is always less than both the other angles.

Question 33:
Study the following four experimental set-ups I, II, III and IV for the experiment, “To trace the path of a ray of light through a rectangular glass slab”.

Which of the marked set-ups is likely to give best results (P1 and P2 are the positions of pins fixed on the incident ray)?
(a) I              (b) II             (c) III              (d) IV
Answer:
(d)
Explanation:
The distance between the two pins should be more than 4-5 cm.

Question 34:
After tracing the path of a ray of light passing through a rectangular glass slab for four different values of the angle of incidence, a student reported his observations in tabular form as given below:

S.No.∠i∠r∠eI30°19°29°II40°28°40°III50°36°50°IV36°40°59°

The best observation is:
(a) I               (b) II              (c) III              (d) IV
Answer:
(c)
Explanation:
∠i = ∠e , ∠i > ∠r.

















Questions on glass slab experiment 10th cbse

CBSE Class 10 Science Lab Manual Practical Based Questions

Question 1:
Out of VIBGYOR, which light bends the least on refraction and which light bends the most?
Answer:
Red light bends the least and violet light bends the most.

Question 2:
State one condition during refraction of light where light does not deviate.
Answer:
When a ray of light is perpendicular to the refracting surface it will not show any deviation.

Question 3:
If a ray of light makes an angle of 30° with the refracting surface, then what will be the angle of incidence?
Answer:
The angle of incidence will be 90° – 30° = 60°.

Question 4:
A ray of light travels from optically denser medium to rarer medium. What will happen to its path?
Answer:
(DRAN) When light travels from optically denser medium to optically rarer medium it bends away from the normal.

Question 5:
Which property of light causes the rainbow formation?
Answer:
The refraction of light due to tiny water droplets in the atmosphere causes rainbow in the sky.

Question 6:
If a ray of light travels from water to oil, in which direction will the light bend?
Answer:
Oil is optically denser than water hence, it will bend towards the normal.

Question 7:
A ray of light travels in the path of normal ray. What will be the angle of incidence?
Answer:
As the ray of light, i.e., incident ray is forming 0° angle with normal ray hence, the angle of incidence is 0°.

Question 8:
Under what condition the emergent ray and incident ray will be parallel?
Answer:
When the angle of incidence is equal to the angle of emergence then both the rays are parallel.

Question 9:
Why does a ray of light bend towards the normal when it enters from air to glass slab?
Answer:
When light travels from rarer medium, i.e., air to the denser medium, i.e., glass slab, its speed decreases and hence it bends to take the shortest path.

Question 10:
On what factor is the lateral displacement of the glass slab dependent?
Answer:
Lateral displacement is dependent on the thickness of glass slab. When the thickness increases the lateral displacement also increases.

Question 11:
Why should we preferably take angle of incidence between 30° and 60°?
Answer:
For angles beyond 30° and 60° the refracted ray may not appear on the opposite face of the glass slab.

Question 12:
Why is emergent ray parallel to the incident ray, after the refraction of incident ray through a glass slab?
Answer:
∠i = ∠e in this case, and these are alternate angles. So, the incident ray is parallel to the emergent ray.

Question 13:
When a ray of light passes through a glass slab, then how many times does it change its path and why?
Answer:
The ray of light bends twice.
First time when it enters from air to the glass slab, it bends towards the normal, i.e., from rarer medium to denser medium.
Second time, when the ray moves out from the glass slab to air, it bends away from the normal, i.e., it moves from denser medium to rarer medium.

CBSE Class 10 Physics Lab Manual Questions

Question 1:
Why are incident and emergent rays parallel to each other in case of a rectangular glass slab?
Answer:
The incident ray and the emergent ray are parallel to each other in case of a rectangular glass slab because the angle of incidence and angle of emergence are same at opposite parallel surfaces of slab.

Question 2:
Why does a ray of light bend towards the normal when it enters from air in a glass slab and bends away from the normal when it emerges out into air?
Answer:
When light enters from air to glass slab its speed decreases and bends towards the normal. But when the light travels from glass slab to air its speed increases and bends away from the normal.

Question 3:
Draw the path of a ray of light when it enters perpendicular to the surface of a glass slab.
Answer:
The path of light when it enters perpendicular to the surface of glass slab would be a straight line passing through
the glass slab.

Question 4:
While tracing the path of ray of light through a glass slab, the angle of incidence is generally taken between 30° and 60°. Explain the reason on the basis of your performing this experiment for different angles of incidence.
Answer:
This is because for any angle greater or smaller than this range (30 degrees to 60 degrees) the emergent ray would not appear on the opposite side of the slab.

Question 5:
How does the lateral displacement of emergent ray depend on the width of the glass slab and angle of incidence?
Answer:
The lateral displacement is directly proportional to the thickness of the glass slab and the angle of incidence.

Lab Manual Class 10 Science Multiple Choice Questions

Questions based on Procedural and Manipulative Skills
Question 1:
In the experiment to trace the path of a ray of light through a rectangular glass slab using pins P1, P2, P3 and P4, four students did the following:
A. Looked at heads of P1 and P2, while placing P3, and heads of P1, P2 and P3 while placing P4 .
B. Looked at feet of P1, P2 while placing P3 and feet of P1, P2 and P3 while placing P4 .
C. Looked at heads of P1 and P2, while placing P3 and feet of all the pins while placing P4.
D. Looked at feet of P1 and P2 while placing P3 and heads of all the pins while placing P4.
The correct procedure is that of student
(a) A               (b) B               (c) C                 (d) D.
Answer:
(b)
Explanation:
It is the correct procedure.

Question 2:
Lateral displacement depends on:
(a) angle of incidence
(b) angle of refraction
(c) thickness of glass slab
(d) angle of emergence.
Answer:
(c)
Explanation:
The bending of light depends on the medium.

Question 3:
If the angle of incidence is 0°, the angle of refraction in the same medium will be:
(a) 90°              (b) 0°
(c) 180°            (d) less than 0°.
Answer:
(b)
Explanation:
As per formula.

Question 4:
The relation between ∠i, ∠r and n (refractive index) is:
(a) n = sin i/sin r
(b) n = sin r/sin i
(c) n sin i = n sin r
(d) sin i = n sin r
Answer:
(a)
Explanation:
Formula of refraction.

Question 5:
A student suggested the following ‘guidelines’ to his friend for doing the experiment on tracing the path of a ray of light passing through rectangular glass slab for three different angles of incidence.
A. Draw the ‘outline’ of the glass slab at three positions on the drawing sheet.
B. Draw ‘normals’ on the top side of these ‘outlines’ near their left end.
C. Draw the incident rays on the three ‘outlines’ in the directions making angles of 30°, 45°, 60° with the normals drawn.
D. Fix two pins vertically on each of these incident rays at two points nearly 1 cm apart.
E. Look for the images of the ‘heads’ of these pins while fixing two pins from the other side, to get the refracted rays.
When he showed these ‘guidelines’ to his teacher, the teacher corrected and modified the ‘guidelines’ labelled as: (The information was insufficient or incorrect)
(a) B, C, E           (b) B, D, E
(c) B, C, D           (d) C, D, E.
Answer:
(b)
Explanation:
It is the correct option.

Question 6:
The incident ray and the emergent ray in the glass slab are:
(a) always parallel               (b) converging always
(c) sometimes parallel        (d) sometimes diverging.
Answer:
(a)
Explanation:
These two rays do not meet.

Question 7:
The speed of light is maximum in:
(a) oil               (b) water
(c) glass           (d) air.
Answer:
(d)
Explanation:
The speed of light is higher in a rarer medium than a denser medium.

Question 8:
In refraction of light, the angle of incidence and angle of refraction is same when:
(a) ∠i = 90°            (b) ∠i = 180°
(c) ∠i = 0°               (d) none of these
Answer:
(c)
Explanation:
As per the formula and law.

Question 9:
When ray of light travels from air to glass slab its wavelength:
(a) increases
(b) no change
(c) decreases
(d) depends on glass slab thickness.
Answer:
(c)
Explanation:
Speed decreases hence wavelength decreases.

Question 10:
The bending of light when it passes from one medium to the other is called:
(a) dispersion          (b) diffraction
(c) refraction            (d) reflection.
Answer:
(c)
Explanation:
Refraction is changing the paths of light when it passes through different media.

Question 11:
In an experiment to trace the path of a ray of light passing through a rectangular glass slab, four students tabulated their observation as given below

The student most likely to have done the experiment properly is
(a) A               (b) B              (c) C              (d) D
Answer:
(a)
Explanation:
We must not only have the angle of emergence
(nearly) equal to the angle of incidence but also have an idea of the magnitude of the angle of refraction (for a glass slab) for the three most often used values (30°, 45°, 60°) of the angle of incidence.

Questions based on Observational Skills
Question 12:
A student traces the path of a ray of light passing through a rectangular glass slab. For measuring the angle of incidence, he must position the protractor in the manner shown in the figure:

(a) A          (b) B            (c) C               (d) D
Answer:
(b)
Explanation:
The angle is measured between the normal ray and the incident ray.

Question 13:
In an experiment on tracing the path of a ray of light passing through a rectangular glass slab, the correct setting of the protractor (D) for measuring the angle of incidence ∠i and the angle of emergence ∠e corresponds, respectively to diagram is:

(a) K and M          (b) K and N
(c) L and M          (d) L and N.
Answer:
(a)
Explanation:
The angles need to be measured from the normal ray.

Question 14:
Four students traced the path of a ray of light from glass to air as shown below. The correct path of refracted ray is:

Answer:
(b)
Explanation:
Denser to rarer and away from the normal.

Question 15:
When light passes from rarer medium to denser medium, the light will bend:
(a) towards the normal
(b) away from normal
(c) depends on thickness of glass slab
(d) depends on the angle of incidence.
Answer:
(a)
Explanation:
(RDTN) The ray from rarer to denser medium bends towards the normal.

Question 16:
In these diagrams, the angle of refraction r is correctly marked in which diagram?

(a) I               (b) II                (c) III                (d) IV
Answer:
(d)
Explanation:
Angle r is between the normal and the refracted ray.

Question 17:
A student traces the path of a ray of white light through a rectangular glass slab and marks the angles of incidence (∠i), refraction (∠r) and emergence (∠e) as shown in the figure. Which angle or angles has he NOT marked correctly?
(a) ∠i only               (b) ∠i and ∠r
(c) ∠i and ∠e           (d) ∠r and ∠e
Answer:
(c)
Explanation:
Angle should be between the normal ray and the incident ray, the normal and the emergent rays.

Question 18:
Four students showed the following traces of the path of a ray of light passing through a rectangular glass slab.

The trace most likely to be correct is that of student:
(a) I                (b) II                (c) III                 (d) IV
Answer:
(c)
Explanation:
The shift of I and E rays is appropriate.

Question 19:
Select from the following the best set-up for tracing the path of a ray of light through a rectangular glass slab:

(a) I                (b) II                 (c) III                  (d) IV
Answer:
(a)
Explanation:
The angle of incidence and distance between two points is appropriate.

Questions based on Reporting and Interpretation Skills
Question 20:
In an experiment to trace the path of a ray of light passing through a rectangular glass slab, four students tabulated their observations as given below:

StudentsABCD∠i30°30°30°30°∠r18°20°17°21.5°∠e32°32.5°30°34.5°

Which student performed the experiment correctly?
(a) A             (b) B               (c) C                (d) D
Answer:
(c)
Explanation:
∠i and ∠e are same and angle r is less than angle i.

Question 21:
A student does the experiment on tracing the path of a ray of light through a rectangular glass slab for different angles of incidence. He can get a correct measure of the angle of incidence and the angle of emergence by following the labelling indicated in figure:

(a) A               (b) B                (c) C                  (d) D
Answer:
(d)
Explanation:
The angle is measured between the normal ray and the incident ray.

Question 22:
A student performs the experiment on tracing the path of a ray of light passing through a rectangular glass slab for different angles of incidence. He measures the angle of incidence ∠i, angle of refraction ∠r and angle of emergence ∠e for all his observations. He would find that in all cases
(a) ∠i is more than ∠r but (nearly) equal to ∠e
(b) ∠i is less than ∠r but (nearly) equal to ∠e
(c) ∠i is more than ∠e but (nearly) equal to ∠r
(d) ∠i is less than ∠e but (nearly) equal to ∠r
Answer:
(a)
Explanation:
∠i and ∠e are same and angle r is less than angle i.

Question 23:
The two dots Pt and P2 shown in each of the following diagrams I, II, III and IV denote the position of two pins in respect of distance and direction for performing an experiment on tracking the path of a ray of light passing through a rectangular glass slab. In which one of the four cases, one is likely to get the best result?

(a) I             (b) II                 (c) III                 (d) IV
Answer:
(c)
Explanation:
Dots P and P, should be on incident ray making an angle of 30 to 60 degree with the normal.

Question 24:
Out of the four set-ups shown for carrying out the experiment to trace the path of a ray of light through a rectangular glass slab, the best set-up is

(a) A              (b) B                 (c) C                  (d) D
Answer:
(b)
Explanation:
Dots should be on incident ray making an angle of 30 to 60 degree with the normal.

Question 25:
In an experiment to trace the path of a ray of light passing through a rectangular glass slab, the correct measurement of angles of incidence (i), refraction (r) and emergence (e) is shown in the diagrams.

(a) A              (b) B                (c) C                (d) D.
Answer:
(a)
Explanation:
∠i = ∠e , ∠i > ∠r.

Question 26:
The path of a ray of light passing through a rectangular glass slab was traced and angles measured. Which one out of the following is the correct representation of an angle of incidence (i), angle of refraction (r) and angle of emergence (e) as shown in the diagrams:

(a) I            (b) II                 (c) III               (d) IV
Answer:
(d)
Explanation:
The angle is always formed between the normal and the ray (incident/refracted/emergent).

Question 27:
An experiment to trace the path of a ray of light through a glass was performed by four students A, B, C and D. They reported the following measurements of angle of incidence i, angle of refraction r and angle of emergence e.

Student∠i∠r∠eA30°30°20°B40°50°40°C40°30°48°D40°30°40°

student performed the experiment correctly?
(a) A           (b) B             (c) C             (d) D
Answer:
(d)
Explanation:
angle i = angle e, angle i > angle r.

Question 28:
The correct path of a ray of light passing from air to kerosene oil and from kerosene oil to water is

(a) A               (b) B              (c) C               (d) D
Answer:
(a)
Explanation:
Ray from rarer to denser medium is towards the normal and from denser to rarer is away from the normal.

Question 29:
A ray of light enters air from water and experiences refraction, then
(a) ∠i = ∠r               (b) ∠i < ∠r
(c) ∠i > ∠r               (d) ∠i / ∠r = 0°.
Answer:
(b)
Explanation:
Light is passing from denser to rarer medium.

Question 30:
Four students A, B, C and D traced the paths of incident ray and the emergent ray by fixing pins P and Q for incident ray and pins R and S for emergent ray for a ray of light passing through a glass slab.

The correct emergent ray was traced by the student:
(a) A              (b) B              (c) C                (d) D
Answer:
(b)
Explanation:
The bending of light is correct (DRAN) and (RDTN).

Question 31:
A ray of light is incident normally, the angle of incidence is:
(a) 90°              (b) 60°             (c) 180°                 (d) 0°.
Answer:
(d)
Explanation:
No angle is made as the incident and the normal rays are straight and same lines.

Question 32:
A student traces the path of a ray of light through a rectangular glass slab for four different angles of incidence. He very cautiously measures the angle i, angle r and the angle e. On analyzing his measurements, he is likely to draw the following conclusion:
(a) ∠i = ∠e < ∠r                (b) ∠i  >  ∠r  > ∠e
(c) ∠i = ∠ r < ∠e               (d) ∠i = ∠e > ∠r
Answer:
(d)
Explanation:
Angle i = angle e, but angle of refraction is always less than both the other angles.

Question 33:
Study the following four experimental set-ups I, II, III and IV for the experiment, “To trace the path of a ray of light through a rectangular glass slab”.

Which of the marked set-ups is likely to give best results (P1 and P2 are the positions of pins fixed on the incident ray)?
(a) I              (b) II             (c) III              (d) IV
Answer:
(d)
Explanation:
The distance between the two pins should be more than 4-5 cm.

Question 34:
After tracing the path of a ray of light passing through a rectangular glass slab for four different values of the angle of incidence, a student reported his observations in tabular form as given below:

S.No.∠i∠r∠eI30°19°29°II40°28°40°III50°36°50°IV36°40°59°

The best observation is:
(a) I               (b) II              (c) III              (d) IV
Answer:
(c)
Explanation:
∠i = ∠e , ∠i > ∠r.