10th Class Physics Chapter 12 Short Questions with Answers Solved

Question: 1

Define Angle of Incidience

Answer: 1

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The angle between the incident ray and the normal is called angle of incidence. It is denoted by "Oi" In given figure angle AON is the angle of incidence

Question: 2

What is meant by reflection of lights?

Answer: 2

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Reflection of Light: The bouncing back of light rays from the surace of a certain medium is called reflection of light.

Explanation: A ray of light travels in one medium but when it falls on the surface of another medium with some angle, it reflects and bounces back to he same medium with same ange. So the amountof ligh reflected from the surface of other medium depends upon the nature and smoothness of that surface.

Question: 3

Refracted ray point of refrection of light.

Answer: 3

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Rafracted ray: The ray of light that is centering the bboundary between two media is called incident refracted ray. In figue, OE is the refrated ray of lihht.

Question: 4

Define Normal

Answer: 4

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The line drawn at right angles to the reflecting surace at the point of incidenc eis called normal in figure, the "ON" is normal to the mirror surface at point "O"

Question: 5

Define point of incidence refraction of light.

Answer: 5

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Point of Incidence: The point at which the inciden try falls on the refrating surfae is called point of incidence. In figure the point "O" on the boundary of glss slab is the point of incidence.

Question: 6

Incident ray refraction of light.

Answer: 6

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The ray of lihght that is entering the bounday between two media is called incident ray. In figure CO is incident ray of lgght.

Question: 7

What is point of incidence.

Answer: 7

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The point at which incidentll ray falls on the reflecting surface is called pointof incidence. In figure, the point "O" on the surface of mirror is thepoint of incidence.

Question: 8

What is Reflected Ray

Answer: 8

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The ray of light which is reflected from a reflecting surace is called reflected ray In figure OB is reflectd ray of light.

Question: 9

Define Angle of reflection Or

Answer: 9

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The angle between the reflected ray and the normal is called angle of reflection. It is denoted by "or" infigue, angle NOB is the angle of reflection.

Question: 10

What is Incident Ray

Answer: 10

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The ray of light whihc fallws on the surface of mirror is called the inident ray In figure AO is the incident ray of light

Question: 11

What is meant by refraction of light?

Answer: 11

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Refraction of Light: The change in direction of light as it moves from one medium to another is called refraction of light.

Question: 12

What is Law of reflection of light

Answer: 12

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1- First Law: The first law states that the incident ray, the reflected ray and the normal to the surface all lie in the same plane.

2- Second Law: According to second law of reflection of light, the angle of incidence "Oi" is always equal to the angle of reflection"Or" i.e.

Qi = Qr

Question: 13

Write applicaton of Optical Fibers

Answer: 13

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1- Internet: Fiber optic This cables transmit large amountof dain at very high speed This technology is therefore widely used in internaet cable.As compared to tible and randitioal coper wires, fibre optic cables are less bulky Lighter and more flexible and carry more data.

2- Cable Television: The use of fibre optic cables in the transimission of cable signals has grown explosively over the years. These cables are ideal for transmitting signals for high definition telveion becasue they have greater bandwidth and speed, Also fiber optic cables are cheaper as compared to the same quantity of copper wire. explosively over the years. These cables are ideal for transimtting signals for high

Question: 14

What is total internal reflection?

Answer: 14

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Total Internal Reflection: When the angle of incidence in the denser medium becomes greater than the crictical angel, becomes greater than the critical angle, there is no refracted beamm.All the rays are intenally reflected back in the optically densermedium. Such a reflection of light is called total internal reflection.

Question: 15

Define Normal to the refraction of light.

Answer: 15

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The line drawn at right angles to the refacting surfae at the point of incidenc is called normal in figure, the line NON is the norml to the surface PQ at the point O.

Question: 16

Write working of Optical Fibers.

Answer: 16

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Varous glasses and plastic can be used to make optical fibres. Optical fibre transmits a beam of light by means of total internal reflectin. Total internal reflection can occur in any tranparent medium that has higher index of of refraction than the surrounding medium As shown infigure the light traveling through the transparent fibre always hits the internal boundary of the opticla fibre at an angle greater than the crictical angle. So, all of the light is reflected and non eof the light is transmitted through the bounday. Thus, the light maintains its intensity over teh distance of the fibre.

Question: 17

Wrie construction of Optical Fibres?

Answer: 17

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Construction: An optical fibre cabel has a clyindrical shape and consists of three concentric sctionns the core, the cladding and the jacket

The core is the innermost sectin and consists of one or mor e very thin strands, made of glass a plastic,Each strand is surruounded by its own cladding,a glass or plastic coating that has optial properties differnet from the core. the boundry betwee the core and cladding acts as a reflector to confine light tha twould otherwiseescape the core. Teh outermost layer. surrounding one or a bundle of cladded fibrs, is the jacket.The jacket is made of plastic and other material layered to protect against moisture, abrasion , curshing and other environmental danges.

Question: 18

When you use a simple magnifying glass, does it matter whether you hold the object to be examined closer to the lens that its focal length or farther away? Explain

Answer: 18

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Question: 19

Define Refractive Index (n):

Answer: 19

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The ratio of the speed of light in vacuum divided by the speed of light is a material is called the refractive index or index of refraction of the material. It is denoted "n" The refractive index is closely related to the velocity of light.

In differnet medium light travels with differnet speed.

Mathematically.

n = speed of light is vacuum or air/ speed of light in any medium

n = C/V

Where the value of C in vacuum is equal to 3 x 10⁸m/s. The speed of light in a physical medium such a glass is always less than the the speed of light in vacuum . There fore, the index of reractionof a metaerial is always greater than or equal to 1. its value si 1 for vacuum.

Question: 20

Law of refracton of Light

Answer: 20

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First law of refration of light: According to first law, "the incident ray refracted ray and the normal at the pointof incidence,all are lie in thesame plane.

Second law of refraction of light: According to second law, "the ratio ofsince of angle of incidenc eand the sine of angle of refractionis constnatfor agiven pair of media" i.e.

Sin Oi/ sin Or= n......................(i)

Question: 21

Define power of Lens and its resolving power. what are its unts.

Answer: 21

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Power of Lens: A convex lens converge the light rays falling on it where as a concave lens diverges the light rays falling on it. The power of a lens is a measur eof the degree of convergence or divergence of light rays falling on it.

Explanation: If a convex lens converage a beam of parallel light rays more storngely by focusing them closer to the optical centre.It is said to have greater power than another convex lens which focuses the same parallel light rays at a greater distance from the opticla center.Teh power of a lens depends onit focal lengh.he smaller the focal length the greater is the coveragence or divergence power of the lens.

D = 1/ Focal length of the lens in.

D = 1/f

Unit: The unit of the power of a lens is diipte. One diopter is the power of a lens whose focal length is 1 meter.

Question: 22

Angle of refraction (Or)

Answer: 22

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The anglebetween the refracted ray and the normal is called angle of refraction. It is denoted b "or" in figur ethe angle EON is the angle of refraction.

Question: 23

What are poticla Fibres.

Answer: 23

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Optical Fibres: Light an be trapped by total interlal reflection inside a bent glass rod and 'piped' along a curved path called optical fibre.

Question: 24

If a concave mirro produces a real image, is the image ncessarily inverted? Explain.

Answer: 24

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A real image is an image formed when light rays actually pasthrogh the point where teh image is formed Real image can be produced by a concave light rays. thus mirror only if the object is plaed beyound focal point of the mirror. This real image will aways be inveted. This is because a concave mirror focuses light rays, thus inverting the real image. However, if the object is plaed between pole "P" and focus "F" the image formed will be upright and virtual not real. That is why it is said that a real image formed by a concave lens will always be inverterted.

Question: 25

Will a nearsighted person who wears orrective lenses in glasses be able to see clearly underwater when wearing those glasses?

Answer: 25

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She will not see clearly under water when wearing those glasses because of the different rerative index of water than aire.

Water has a refractive index of 1.33 which is much greater than that of air . The high refractive inxed of water affects the refraction of light rays due to which she will not be able to see clearly in water by wearing glasses having corrective lenses.

Question: 26

What is Criticla Angle

Answer: 26

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To construct an equation for the critical angle of any boundary, we can use Snell's law and substitute Oi = Oc and O2 = 90 o

n1sin Oc = n2 sin 90 o

There fore n1sin Oc = n2

Hence sin Oc= n2/n1

Thus we can define critical angle as "the sine of the critical angle is equal to the index of refraction of the refracting medium divided by teh index of refractionof the incident medium".

Question: 27

Can we ahieve total internal reflection from optically rare medium to optically dense medium?

Answer: 27

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Question: 28

In blind turns on hilly roads, mirros are used to help drivers. Are these mirrors plane mirrors, concae mirrors or convex mirrors ? Explain

Answer: 28

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Question: 29

Define Angle of incidence Oi.

Answer: 29

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The angle between teh incident ray and the normal is called angle of incidence. It is denoted by "oi" in figure ,angle CON is the angle of incidence.

Question: 30

Which type of lens would you use to start fire from light from sun concave or convex, would work best? AT what distance from the lens should the paper be held for best results?

Answer: 30

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Question: 31

Suppose that you wee handed a lens and a ruler and told to determine the focal length of the lens. How would you proceed.

Answer: 31

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We can easily find the focal length of a lens usng ruler in open air make the rays foused on a wall and measure teh distance between the lens and the wall with the help of meter rod. This will be the focal length of the given lens.

Question: 32

Wrie condition for Total Internal Reflection.

Answer: 32

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1- The light must travel from an optically more dense medium into an optically less dense medium.

2- The angle of incidene must exceed the critical angle, 0c, associated with the material.

Question: 33

What is a compound microscope? and working.

Answer: 33

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Compound Microcope: Tbe compound microscope is an instrument whcih is used for observing small obejects clearly.

Question: 34

Are rearivew mirrors use in cars concave or convex.

Answer: 34

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Convex mirror are useful for rare view in vehicles, as they privide a largest field of view than the convcave mirro.Convex mirrors give erect, virtual and diminshed image of distant objets with a wider field of view.

On the other hand, conave mirror forms inverted images of the distant objects with a smaller field of view . Thus for a broader field of view, erect and clear images, conve mirrors are sued.

Question: 35

What is a simple microscope? Working principal and working.

Answer: 35

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Simple Microscope: A simple microscope is a convex lens of short focal length. It is also called magnifying glass.

Working Principal: It work on the principal that when teh object is placed with in its focal length, a magnified virtual and erect image is formed.

Working : The simple microscope is an ordinary convex lens of small focal length which is held closer to eye for magnifying the image.

Now consi of there an object"AB" is placed between the lens and its focus as shown in figure. The lens form a magnifed, virtual and exec imge "A"B"

of the object "AB" which can be see clearly by an eye wich is held closer to the lens.

Question: 36

Define Short Sigteness and Long Sitness.

Answer: 36

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Short Sighteness: Short sighteness is that defet of the eye due to which an eye annot see the distinct object clearly though it can see the near by objects clearly

Cause: This defect of eye is caused due to high converging power of the cyc-lens, or due to eye ball too long.

Question: 37

A magician duirng a show makes a glass less with n=1.47 disappear in a trough of liquid, What is the refraactive index of teh liquid ? Could the liquid be water?

Answer: 37

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10th Class Chapter 12 Physics Short Questions

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