Magnification in Thin Lens

Q. A compound microscope has an eye piece of focal length $10cm$ and an objective of focal length $4cm$. Calculate the magnification, if an object is kept at a distance of $5cm$ from the objective so that final image is formed at the least distance vision $\left(20cm\right)$.

1. $12$
2. $11$
3. $10$
4. $13$

Q. If the focal length of objective lens is increased then magnifying power of

1. microscope will increase but that of telescope
2. microscope and telescope both will increase
3. microscope and telescope both will decrease
4. microscope will decrease but that of telescope increase

Q. A compound microscope consists of an objective lens of focal length $1\text{cm}$ and an eye piece of focal length $5\text{cm}$ with a separation of $10\text{cm}$. The distance between an object and the objective lens, at which the strain on the eye is minimum is $\frac{n}{40}\text{cm}$. The value of $n$ is

Q. In a compound microscope, the focal length of objective lens is $1.2\text{cm}$ and that of eyepiece is $3\text{cm}$. When the object is kept at $1.25\text{cm}$ in front of the objective, the final image is formed at infinity. Magnifying power of the compound microscope is

1. $400$
2. $200$
3. $150$
4. $100$

Q. The focal length of the objective and eyepiece of a microscope are $2\text{cm}$ and $5\text{cm}$ respectively, and the distance between them is $20\text{cm}$. Find the distance of the object from the objective, when the final image seen by the eye is $25\text{cm}$ from the eyepiece.

1. $3\text{cm}$
2. $2.3\text{cm}$
3. $3.2\text{cm}$
4. $4\text{cm}$

Q. The objective lens of a compound microscope produces magnification of $10$. In order to get an overall magnification of $100$ when image is formed at $25cm$ from the eye, the focal length of the eye piece should be

1. $4cm$
2. $10cm$
3. $\frac{25}{9}cm$
4. $9cm$

Q. In a compound microscope, the focal length of the objective lens is $1.2\text{cm}$ and the focal length of the eyepiece is $3\text{cm}$. When the object is kept at $1.25\text{cm}$ in front of the objective lens, the final image is formed at infinity. The magnifying power of the compound microscope is -

1. $400$
2. $200$
3. $150$
4. $100$

Q. The magnifying power of a compound microscope can be increased by -

$\left(i\right)$ Using both the lenses of larger focal lengths.

$\left(ii\right)$ Using both the lenses of smaller focal lengths.

$\left(iii\right)$ Decreasing the object distance from the objective lens, but keeping $u_o>f_o$.

1. Only $\left(i\right)$
2. $\left(i\right)$ and $\left(ii\right)$
3. $\left(i\right)$ and $\left(iii\right)$
4. $\left(ii\right)$ and $\left(iii\right)$

Q.

An object is to be seen through a simple microscope of focal length 12 cm. Where should the object be placed so as to produce maximum angular magnification? The least distance for clear vision is 25 cm.

Q. The separation $L$ between the objective $(f=0.5cm)$ and the eyepiece $(f=5cm)$ of a compound microscope is $7cm$.

If a small object be placed so that the eye is least strained to see the image, find the angular magnification produced by the microscope.

1. $20$
2. $15$
3. $\frac{5}{3}$
4. $25$

Q.

In a compound microscope, maximum magnification is obtained when the final image

1. Is formed at the least distance of distinct vision

2. Is formed at infinity

3. Coincides with the object

4. Coincides with the objective lens

Q. The focal lengths of the objective and the eyepiece of a compound microscope are $1\text{cm}$ and $5.0\text{cm}$ respectively. An object, placed at a distance of $1.1\text{cm}$ from the objective, has its final image formed at infinity. The distance between the lenses will be $\left(\text{in cm}\right)$.

Q. A man is looking at a small object placed at his near point. Without altering the position of his eye or the object, he puts a simple microscope of magnifying power $5\text{X}$ before his eyes. The angular magnification achieved is

1. $5$
2. $2.5$
3. $1$
4. $0.2$

Q.

An eye can distinguish between two points of an object if they are separated by more than 0.22 mm when the object is placed at 25 cm from the eye. The object is now seen by a compound microscope having a 20 D objective and 10 D eyepiece separated by a distance of 20 cm. The final image is formed at 25 cm from the eye. What is the minimum separation between two points of the object which can now be distinguished?

Q. In compound microscope the magnification is $95$, and the distance of object from objective lens $\frac{1}{3.8}\text{cm}$ and focal length of objective is $\frac{1}{4}\text{cm}.$ What is the magnification of eye piece when final image is formed at least distance of distinct vision ?

1. $5$
2. $10$
3. $100$
4. None of the these

Q. In a compound microscope, the magnified virtual image is formed at a distance of $25\text{cm}$ from the eye-piece. The final image formed at a distance lens $1\text{cm}.$ If the magnification is $100$ and the tube length of the microscope is $20\text{cm},$ then the focal length of the eye-piece lens (in $\text{cm}$) is close to (up to two decimal places)

Q. In case of a compound microscope, an angular magnification of $30X$ is to be achieved using an eyepiece of focal length $5\text{cm}$ and an objective lens. Find the magnifying power of objective lens if the angular magnification is achieved in case of normal adjustment.

1. $6$
2. $7$
3. $8$
4. $9$

Q. Which of the following options is correct?

$f_o$ is the focal length of the objective lens and $f_e$ is the focal length of the eyepiece of a compound microscope.

1. The magnification depends only on $f_o$.
2. The magnification depends only on $f_e$.
3. The magnification depends on both $f_o$ and $f_e$.
4. The magnification is independent of focal lengths of both objective lens and eyepiece.

Q. An object is placed at a distance $u$ from a simple microscope of focal length $f$. The angular magnification obtained depends

1. on $f$ but not on $u$
2. on $u$ but not on $f$
3. on $f$ as well as $u$
4. neither on $f$ nor on $u$

Q. When the object is placed at $4\text{cm}$ from the objective lens of the compound microscope, the final image is formed at the position of the object which is the least distance of distinct vision $\left(24\text{cm}\right)$. If the focal length of the eyepiece is $8\text{cm}$ then the focal length of the objective lens is -

1. $3\text{cm}$
2. $2\text{cm}$
3. $4\text{cm}$
4. $5\text{cm}$

Q. An object is to be seen through a simple microscope of focal length $10\text{cm}$. Where should the object be placed to produce maximum angular magnification?

The least distance for clear vision for the eye is $30\text{cm}$.

1. $8.5\text{cm}$
2. $7.5\text{cm}$
3. $6.5\text{cm}$
4. $9.5\text{cm}$

Q. An angular magnification of $30\text{X}$ is to be obtained from a compound microscope, having an eyepiece of focal length $5\text{cm}$. Find the magnification produced by the objective lens.

Given angular magnification is achieved in case of the least strain on the eye.

1. $6$
2. $7$
3. $8$
4. $9$

Q. An object is to be seen through a simple microscope of focal length $10\text{cm}$. Where should the object be placed to produce maximum angular magnification? (The least distance for clear vision is $30\text{cm})$.

1. $8.5\text{cm}$
2. $7.5\text{cm}$
3. $6.5\text{cm}$
4. $9.5\text{cm}$

Q. A compound microscope has a magnifying power of $100$ when the image is formed at infinity. The objective has a focal length of $0.5\text{cm}$ and the tube length is $6.5\text{cm},$ then the focal length of the eye-piece is -

1. $0.2\text{cm}$
2. $2.5\text{cm}$
3. $2\text{cm}$
4. $4.0\text{cm}$

Q. You are given two converging lenses of focal lengths, $1.5\text{cm}$ and $4\text{cm}$ to design a compound microscope. If it is desired to have a magnifying power of $50$, in case of normal adjustment, then find out the separation between the objective lens and the eyepiece.

1. $15\text{cm}$
2. $12\text{cm}$
3. $25\text{cm}$
4. $30\text{cm}$

Q. The focal length of the objective and eyepiece of a microscope are $2\text{cm}$ and $5\text{cm}$ respectively and the distance between them is $20\text{cm}.$ Find the distance of object from the objective, when the final image seen by the eye is $25\text{cm}$ from the eyepiece.

1. $8\text{cm}$
2. $4\text{cm}$
3. $3.6\text{cm}$
4. $2.3\text{cm}$

Q. In a microscope, the focal lengths of two lenses are $1.5\text{cm}$ and $6.25\text{cm}.$ If an object is placed at $2\text{cm}$ from objective and final image is formed at $25\text{cm}$ from eye-lens, the distance between two lenses is -

1. $6\text{cm}$
2. $7.75\text{cm}$
3. $9.25\text{cm}$
4. $11\text{cm}$

Q. In a compound microscope the focal length of an objective lens is $1.2\text{cm}$ and the focal length of the eye piece is $3\text{cm}$. When the object is kept at $1.25\text{cm}$ in front of the objective lens, the final image is formed at infinity. Magnifying power of the compound microscope should be:

1. $400$
2. $200$
3. $150$
4. $100$

Q. A compound microscope has a magnification of $30$. The focal length of the eye-piece is $5$ cm. If the final image is formed at the least distance of distinct vision $25cm$, the magnification produced by the objective is

1. $5$
2. $10$
3. $15$
4. $7.5$

Q. A compound microscope having magnifying power 35 with its eye-piece of focal length 10 cm. Assume that the final image is at least distance of distinct vision then the magnification produced by the objective is

1. 5
2. 10
3. -4
4. -10