11th Class Physics Chapter ten Short Questions with Answers Solved

Question: 1

What do you mean by "Normal adjustment " in an astronomical telescope?

Answer: 1

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In normal adjustment, the image formed by the objective lies at the focus of both the objective and the eye-piece and the final image appears to be formed at infinity. The distance between the objective and eye-piece of a telescope in normal adjustment is f_o+f_{e which equals the length of the telescope.}

Question: 2

What do you understand by linear magnification and angular magnification?Explain how a convex lens is used as magnifier ?

Answer: 2

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Linear Magnification: is the ratio of the size of the image to the size of object.

Angular Magnification: is the ratio of the angle subtended by the image as seen through the optical device to that subtended by the object at the naked eye placed at near point

A convex lens of shorter focal length can be used as a magnifier when the object is placed very close to it.i.e When it lies between the lens and its focus.The image then formed is virtual, erect and magnified.

Question: 3

What do you understand by Linear Magnification?

Answer: 3

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Linear magnification is the ratio of the size of the image to the size of object.Angular magnification is the ratio of the angle subtended by the image as seen through the optical device to that subtended by the object at the naked eye placed at least distance of distinct vision.

Question: 4

One can buy a cheap microscope for used by the children. The image seen in such a microscope has coloured edges.Why is this so?

Answer: 4

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It is due to the defects of lenses known a chromatic aberrations. This is because of the prism like formation of the lens which causes dispersion of white light.

Question: 5

If the person was looking through a telescope at thee full moon, how would the appearance of the moon be changed by covering half of the objective lens?

Answer: 5

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How will see the full moon still but the brightness will be reduced because less light is transmitting through the half covered lens.

Question: 6

Why would it be advantageous to use blue light with a compound microscope?

Answer: 6

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Question: 7

Define Magnification.

Answer: 7

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The size of the object goes on increasing, when the object brought from a far off point to the focus of the lens. This phenomenon of enlargement is called magnification. Its is the ration of size of image to the size of object.

Question: 8

What are the problems having a high magnifying power in astronomical telescope?

Answer: 8

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High magnifying power in astronomical telescope was accompanied by more spherical an chromatic aberration, geometric distortion and false colors.

Question: 9

What is the near point? Give its numerical value?

Answer: 9

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The minimum distance from the eye at which an object appears to be distinct is called near point or least distance of distinct vision.

Its numerical value is 25 cm

The location of the near point, however , change with age.

Question: 10

Differentiate between microscope and telescope.

Answer: 10

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Microscope is a device which is used to see the magnified image of very small and near object. Whereas telescope is an optical instrument used for viewing distant objects.

Question: 11

How Convex Lens act as magnifying glass?

Answer: 11

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A convex lens of shorter focal length can be used as a magnifier when the object is placed very close to it I.e. When it lies between the lens and its focus. The image then formed is virtual, erect and magnified.

Question: 12

When object lie within the principle focus of convex lens what is the nature of image and where it is formed?

Answer: 12

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When object lie within the principle focus of convex lens, then image will be virtual, erect and magnified and will be formed at least distance of distinct vision.

Question: 13

Why we use infrared light in a fiber optics communication system?

Answer: 13

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Infrared light travels faster through optical fiber than visible light. So, it is preferred.

Question: 14

Define total internal reflection.

Answer: 14

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For glass-air boundary, when a propagating wave strikes the boundary at an angle larger than critical angle with respect to the normal to the surface, all the light is reflected and none is refracted to the air. This phenomenon is called total internal reflection.

Question: 15

Write the advantages of using light as transmission carrier wave over radio wave carriers.

Answer: 15

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The use of light as transmission carrier wave in fibre optics gas several advantages over radio wave carriers such as a much wider bandwidth capability and immunity from electromagnetic interference.

Question: 16

Define total internal reflection and continuous refraction.

Answer: 16

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Total Internal Reflection:When a light ray traveling from a denser medium towards a rare medium, makes an angle of incidence greater than critical angle of the medium, then the ray is totally reflected back into the same denser medium. This phenomenon is called total internal reflection.

Continuous Refraction: It is the mode of propagation of light in which light is continuously refracted inside the different graded index fibers which are used in fibre optics.

Question: 17

Define Snell's law and write its mathematical form.

Answer: 17

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Snell's law states that the ratio of the sines of the angles of incidence and refraction of a wave are constant when it passes between two given media. OR Snell' Law is a formula used to describe the relationship between the angles of incidence and refraction, when referring to light or other waves passing through a boundary between two different isotropic media such as water, glass, or air.

Question: 18

What are different types of optical fibre?

Answer: 18

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There are three types of optical fibres.

Single mode step index fibre.
Multimode step index fibre.
Multimode graded index fibre.

Question: 19

What is the function of collimator in a spectrometer?

Answer: 19

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Collimator is used to make the light rays parallel. It consists of a fixed metallic tube, a convex lens and an adjustable slit.

Question: 20

What is the condition for total internal reflection?

Answer: 20

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For glass- air boundary , when a propagating wave strikes the boundary at an angle larger than critical angle with respect to the normal to the surface, all the light is reflected and none is refracted to the air. This phenomenon is called total internal reflection. When a light ray travelling from a denser medium towards a rare medium, makes an angle of incidence greater than critical angle of the medium, then the ray is totally reflected back into the same denser medium.

Question: 21

What is spectrometer?

Answer: 21

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Spectrometer is a device which is used to study the spectra from different light sources.

Its main parts are

Collimator
Turntable
Telescope

Question: 22

Write down the three major components on which a fibre communication system consists.

Answer: 22

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A fibre communication system consist of

Transmitter
Optical fibre
Receiver

Question: 23

Write any two uses of spectrometer.

Answer: 23

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It is used to study spectra from different sources of light.Its is used to determine the wavelength of light.

Question: 24

A magnifying glass gives a five time enlarged image at a distance of 25 cm from the lens. What will be the focal length of the lens?

Answer: 24

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Question: 25

A telescope is made an objective of focal length 20 cm and eye-piece of 5 cm, both convex lenses. Find the magnifying power of telescope.

Answer: 25

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Question: 26

What are uses of spectrometer?

Answer: 26

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It is used to study spectra from different sources of light. Determine the wavelength of light by grating. Study the deviation of light by glass prism.

Calculate refractive index of prism material

Question: 27

What is resolving power in optical instrument? Write formula for grating.

Answer: 27

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Question: 28

Find magnifying power of a convex lens of 25 cm focal length act as a magnifying glass.

Answer: 28

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Question: 29

Answer: 29

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Question: 30

How the power is lost in Optical fibre?

Answer: 30

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If light is not perfectly monochromatic, power is lost due to dispersion (or spreading of the light signal). Some light is absorbed due to impurities in the glass. Some light is scattered by groups of atoms which are formed at places such as joints when fibres are joined together.

Question: 31

Find the magnifying power of a convex lens of 10 cm focal length.

Answer: 31

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Question: 32

How light signals is transmitted through optical fibre?

Answer: 32

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The lights signal are transmitted through the optical on the principle of

Total internal reflection
Continuous refraction

In multimedia step index fiber, the signal is transmitted baby means of total internal reflection while in case of multimode graded index fiber, the signals transmitted by total internal reflection and continuous refraction.

Question: 33

Focal length of convex lens is 5 cm, calculate its magnification.

Answer: 33

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Question: 34

An astronomical telescope of long focal length and large aperture is considered to be a good telescope. Why?

Answer: 34

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Objective of long focal length and large aperture is used to collect a great amount of light from the astronomical objects.

Question: 35

Differentiate between multimode step index and multimode graded index fibre.

Answer: 35

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11th Class Chapter ten Physics Short Questions

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