Draw a labelled diagram of simple microscope and establish an expression for the magnifying power of simple microscope, when the image formed at ii Least distance of distinct vision.

Expression of magnifying power of a compound microscope is given by: m = V 0 u 0 1 D f e Where V 0 is the image distance from the objective lens D is the least distance of distinct vision f e is the focal length of eye lens.

Draw a labelled diagram of simple microscope and establish an expression for the magnifying power of simple microscope, when the image formed at i Infinity

A simple microscope has a limited maximum magnification (≤ 9) for realistic focal lengths. For much larger magnifications, one uses two lenses, one compounding the effect of the other. This is known as a compound microscope. A schematic diagram of a compound microscope is shown in above figure.The lens nearest the object, called the objective, forms a real, inverted, magnified image of the object. This serves as the object for the second lens, the eyepiece, which functions essentially like a simple microscope or magnifier, produces the final image, which is enlarged and virtual.The first inverted image is thus near (at or within) the focal plane of the eyepiece, at a distance appropriate for final image formationat infinity, or a little closer for image formationat the near point. Clearly, the final image is inverted with respect to the original object. We now obtain the magnification due to a compound microscope. The ray diagram given in figure shows that the (linear) magnification m o due to the objective, namely h ' / h , equals m 0 = h ' h = L f 0 To get magnification m o due to objective as given above, we have used the properties of similar triangles appearing between objective lens and first image as given below. tanβ = h f 0 = h ' L Here h′ is the size of the first image, the object size being h and fo being the focal length of the objective. The first image is formed near the focal point of the eyepiece. The distance L, i.e., the distance between the second focal point of the objective and the first focal point of the eyepiece(focal length f e ) is called the tube length of the compound microscope. As the first inverted image is near the focal point of the eyepiece, we use the magnification expression for the simple microscope to obtain the (angular) magnification m e . When the final image is formed at the near point, is m e = 1 + D f e When the final image is formed at infinity, the angular magnification due to the eyepiece is m e = D f e Thus, the total magnification, when the image is formed at infinity, is m = m o m e = L f o D f e Clearly, to achieve a large magnification of a small object (hence the name microscope), the objective and eyepiece should have small focal lengths.

Establish the relation 1 f = 1 v - 1 u for a convex lens, where symbols have their usual meanings.

The figure above shows that the formation of a real, inverted and diminished image AB of the object AB placed beyond the centre of curvature at a distance u from the convex lens. Let v be the image distance, According to Cartesian sign convention Object distance ( OB ) = − u Image distance ( OB ' ) = + v Focal length ( OF 1 = OF 2 ) = + f From the geometry of the figure above , right angled △ ABO and △ AB ' O are similar . ∴ AB A ' B ' = OB O ' B ' = − v . . . . . . . . ( i ) Similarly , from the geometry of the figure above , right angled △ ODF 2 and △ BAF 2 are similar . ∴ OD A ' B ' = OF 2 F 2 B 2 ∴ AB A ' B ' = OF 2 F 2 B 2 ∵ OD = AB , are the opposite sides of □ ABOD ∴ AB A ' B ' = OF 2 OB ' - OF 2 ∴ AB A ' B ' = f v - f . . . . . . . . ( ii ) - u v = v v - f ⇒ - u v - f = vf ⇒ - uv + uf = vf Dividing each term by uvf - 1 f + 1 v = 1 u 1 v - 1 u = 1 f This equation is called the ' Lens formula ' . Where, f is focal length v is denoted as the distance of the image from the optical center. u is denoted as the distance of the object from the optical center In convex lens, the focal length is positive.

E M B I B E

EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR PHYSICS>Chapter 9 - Ray Optics and Optical Instruments>Madhya Pradesh Board-2020>Q 21

EASY

12th Madhya Pradesh Board

IMPORTANT

Earn 100

Value of absolute refractive index of water is:

50% studentsanswered this correctly

Important Questions on Ray Optics and Optical Instruments

MEDIUM

12th Madhya Pradesh Board

IMPORTANT

EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR PHYSICS>Chapter 9 - Ray Optics and Optical Instruments>Madhya Pradesh Board-2020>Q 22

The magnifying power of objective lens of compound microscope is

06

and eye lens is

05

. Find the net magnifying of compound microscope.

MEDIUM

12th Madhya Pradesh Board

IMPORTANT

EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR PHYSICS>Chapter 9 - Ray Optics and Optical Instruments>Madhya Pradesh Board-2020>Q 23

Write the conditions for obtaining total internal reflection. Write its any two applications.

MEDIUM

12th Madhya Pradesh Board

IMPORTANT

EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR PHYSICS>Chapter 9 - Ray Optics and Optical Instruments>Madhya Pradesh Board-2020>Q 24

Derive the expression for combined focal length of two thin lenses kept in contact.

EASY

12th Madhya Pradesh Board

IMPORTANT

EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR PHYSICS>Chapter 9 - Ray Optics and Optical Instruments>Madhya Pradesh Board-2020>Q 25

A $5 cm$ long object is placed in front of a concave mirror of radius of curvature $40 cm$ . The distance of object from mirror is $40 cm$ . Find the distance and size of the image.

Question Image