Magnification in Thin Lens

Q. If we need a magnification of 375 from a compound microscope of tube length 150 mm and an objective of focal length 5 mm, the focal length of the eye-piece should be close to:

1. 22 mm
2. 2 mm
3. 12 mm
4. 33 mm

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. 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. 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. The object distance u, the image distance v and the magnification m in a lens follow certain linear relations. These are

1. $\frac{1}{u}$ versus $\frac{1}{v}$
2. m versus u
3. u versus v
4. m versus $\frac{1}{u}$

Q. A convex lens of focal length f is placed somewhere in between an object and a screen. The distance between the object and the screen is x. If the numerical value of the magnification produced by the lens is m, then the focal length of the lens is

1. $\frac{mx}{(m+1{)}^2}$
2. $\frac{mx}{(m-1{)}^2}$
3. $\frac{(m+1{)}^2}{m}x$
4. $\frac{(m-1{)}^2}{m}x$

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. A convex lens is in contact with a concave lens. The magnitude of the ratio of their focal lengths is $\frac{2}{3}$. Their equivalent focal length is 30cm. What are their individual focal lengths?

1. -15, 10
2. -10, 15
3. 75, 50
4. -75, 50

Q. A convex lens of focal length f is placed somewhere in between an object and a screen. The distance between the object and the screen is x. If the numerical value of the magnification produced by the lens is m, then the focal length of the lens is

1. $\frac{mx}{(m+1{)}^2}$
2. $\frac{mx}{(m-1{)}^2}$
3. $\frac{(m+1{)}^2}{m}x$
4. $\frac{(m-1{)}^2}{m}x$

Q. If we need a magnification of 375 from a compound microscope of tube length 150 mm and an objective of focal length 5 mm, the focal length of the eye-piece should be close to:

1. 22 mm
2. 2 mm
3. 12 mm
4. 33 mm