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A biconvex lens of focal length f is cut into two identical plano convex lenses. The focal length of each part will be
Option: 1 f
Option: 2 \frac{f}{2}
Option: 3 2f
Option: 4 4f

The focal length of each part will be 2f

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Safeer PP

A biconcave lens of power P vertically splits into two identical plano concave parts. The power of each part will be
Option: 1 2P
Option: 2 \frac{P}{2}
Option: 3 P
Option: 4 \frac{P}{\sqrt{2}}

power of each part will be P/2

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Safeer PP

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Larger aperture of objective lens in an astronomical telescope
Option: 1 increases the resolving power of telescope.
Option: 2 decreases the brightness of the image.
Option: 3 increases the size of the image.
Option: 4 decreases the length of the telescope.

A telescope has a much larger aperture and therefore has a greater resolving power.

 

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Safeer PP

For a glass prism, the angle of minimum deviation will be smallest for the light of
Option: 1 red colour.
Option: 2 blue colour.
Option: 3 yellow colour.
Option: 4 green colour.

The angle of minimum deviation will be smallest for the red light

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Safeer PP

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A biconvex lens of glass having refractive index 1.47 is immersed in a liquid. It becomes invisible and behaves as a plane glass plate. The refractive index of the liquid is
Option: 1 1.47
Option: 2 1.62
Option: 3 1.33
Option: 4 1.51

The ray will pass un deviated through it only when the medium has the same refractive index as that of the biconvex lens

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Safeer PP

Rhapsody in Blue was written by which American composer?

Rhapsody in Blue was written by Paul Whitman.

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Deependra Verma

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What is Ghana vadhya ?

Ghana Vadya is a type of  music instrument. It was the earliest instrument invented by men. Ghana vadya are also known as idiophones. Examples of Ghana vadhya are Manjira, Gong etc.

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Deependra Verma

For a glass prism \mu=\sqrt{3} the angle of minimum deviation is equal to the angle of the prism. Find the angle of the prism.

The refractive index of prism angle A and angle of minimum deviation \delta _{m} is given by

\mu=\frac{\sin\left [ \frac{\left ( A+\delta _{m} \right )}{2} \right ]}{\sin\left ( \frac{A}{2} \right )}

Here we are given, \delta _{m}=A

Substituting the value, we have

\mu=\frac{\sin A}{\sin \frac{A}{2}}

\Rightarrow \mu=\frac{2\sin\frac{A}{2}\cos\frac{A}{2}}{\sin\frac{A}{2}}=2 \cos\frac{A}{2}

\Rightarrow \mu=\frac{\sin A}{\sin \frac{A}{2}}=\frac{2\sin\frac{A}{2}\cos\frac{A}{2}}{\sin\frac{A}{2}}=2 \cos\frac{A}{2}

For the given value of refractive index,

We have, \cos\frac{A}{2}=\frac{\sqrt{3}}{2}\Rightarrow \frac{A}{2}=30^{o}

Or A=60^{o}

This is the required value of prism angle.

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infoexpert23

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An unsymmetrical double convex thin lens forms the image of a point object on its axis. Will the position of the image change if the lens is reversed?

Explanation:-

For a given object position if the focal length of the lens does not change, the image position remains unchanged.

By lens maker's formula,

\frac{1}{f}=\left ( \mu -1 \right )\left ( \frac{1}{R_{1}}-\frac{1}{R_{2}} \right )          

For this position R_{1} is positive

and R_{2} is negative. Hence focal length at this position

\frac{1}{f_{1}}=\left ( \mu -1 \right )\left ( \frac{1}{\left ( +R_{1} \right )}-\frac{1}{\left ( -R_{2} \right )} \right )=\left ( \mu -1 \right )\left ( \frac{1}{R_{1}}+\frac{1}{R_{2}} \right )

Now the lens is reversed,

At this position, R_{2} is positive and R_{1} is negative. Hence focal length at this position is

\frac{1}{f_{2}}=\left ( \mu -1 \right )\left ( \frac{1}{\left ( +R_{2} \right )}-\frac{1}{\left ( -R_{1} \right )} \right )=\left ( \mu -1 \right )\left ( \frac{1}{R_{1}}+\frac{1}{R_{2}} \right )

We can observe the focal length of the lens does not change in both positions, hence the image position remains unchanged.

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infoexpert23

The near vision of an average person is 25cm. To view an object with an angular magnification of 10, what should be the power of the microscope?

 

In the given question, the least distance of distinct vision of an average person is 25 cm, in order to view an object with magnification 10,

Here,

v=D=25\; cm\; and\; u=f

But the magnification

m=\frac{v}{u}=\frac{D}{f}

\Rightarrow f=\frac{D}{m}=\frac{25}{10}=2.5 \; cm=0.025\; m

But power

P=\frac{1}{f(in\; m)}=\frac{1}{0.025}=40\; D

This is the required power of the lens.

 

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infoexpert23

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