Q # 1: What do you understand by linear magnification and angular magnification? Explain how a convex lens is used as a magnifier?
Linear Magnification: The ratio of the size of image to the size of object is called linear magnification.
Angular Magnification: The ratio of the angle subtended by the image as seen through the optical device to that subtended by the object at the un-aided eye
Convex Lens as a Magnifier: A convex lens of short focal length can be used as magnifying glass because when an object is placed close to the lens then the image formed is erect, virtual and very much magnified.
Q # 2: Explain the difference between the angular magnification and resolving power of optical instrument. What limits the magnification of an optical instrument?
Ans. Angular magnification means how large or magnified image is formed by the instrument but resolving power is its ability to provide the details of an object under examination.
The magnification of an optical instrument is limited due to defects in the lenses, such as chromatic and spherical aberrations.
Q # 3: Why would it be advantages to use blue light with compound microscope?
Ans. If blue light is used in compound microscope, it increases the resolving power and more details on an object can be studied.
Q # 4: One can buy cheap microscope for use of children. The images seen in such microscope have colored edges, why is this so?
Ans. The images in microscope have colored edges because of defects in lenses. Such a defect is known as chromatic aberration. In such a problem, a lens can't bring all rays of white light to a single point on image. So image is not sharp and has colored edges.
Q # 5: Describe with the help of diagrams, how (a) a single biconvex lens can be used as a magnifying glass.(b) biconvex lenses can be arranged to form a microscope.
Ans.
Q # 6: If a person looking through microscope at the full moon, how would the appearance of moon be changed by covering of objective lens?
Ans. The person will see the full image of the moon if half of the objective lens of a telescope is covered but its brightness is reduced because less light is transmitted through the lens.
Q # 7. A magnifying glass gives five times enlarge image at the distance of 25 cm from the lens. Find, by the ray diagram the focal length of lens.}
Ans. Magnification M = 5
Image distance = 25 cm
Focal length of lens = ?
$$\begin{aligned}& A s M=1+\frac{d}{f} \Rightarrow \frac{d}{f}=M-1 \\& \Rightarrow f=\frac{d}{M-1}=\frac{25}{5-1}=\frac{25}{4}=6.2 \mathrm{~cm}\end{aligned}$$
Q # 8: Identify the correct answer.
1. The resolving power of a compound microscope
depends on:
a)
The refractive index of the medium in which the
object is placed.
b)
The diameter of the objective lens.
c)
The angle subtended by the objective lens at the
object.
d)
The position of an observer's eye with regard to
the eye lens.
Ans. Option (b) is correct
2.
The resolving power of an astronomical telescope
depends on:
a)
The focal length of the objective lens
b)
The least distance of distinct vision of the
observer
c)
The focal length of the eye lens
d)
The diameter of the objective lens
Ans. Option (d) is correct
Q # 9.Draw sketches showing the different light paths through a single-mode and multi-mode fibre. Why is the single-mode fibre preferred in telecommunications?
Ans. Single Mode fiber optic cable has a small diameter core that allows only one mode of light to propagate. Because of this, the number of light reflections created as the light passes through the core decreases, lowering attenuation and creating the ability for the signal to travel further. That's why, single mode fibre optic is preferred in telecommunication.
Q # 10.How the light signal is transmitted through the optical fibre?
Pulse of light represented by ``1'' and absence of light is represented by ``0''. Any information can be represented by the pattern of 1's and 0's transmitted through fibre optic to transfer information from one point to another.
Q # 11. How the power is lost in optical fibre through dispersion? Explain.
Ans. If the source of light signals is not monochromatic then, the light will disperse while propagating through the core of the optical fibre into different wavelength so the light of different wavelengths reaches the other end of the fibre at different times and the signal received is distorted. So the power is lost in optical fibre through dispersion.
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