Lens Maker's Formula

Q. The lower end of capillary tube of diameter d is placed vertically in a liquid of density ρ, then with the rise of liquid in capillary to height h, heat evolved is

Q. if f is focal length of lens & the separation of central maximum from first null of diffraction pattern is (lamda)/a in term of angle, then size of screen is f(lamda)/a . How?

Q. A equiconvex lens of focal length $20\text{cm}$ is cut into two equal parts to obtain two plano- convex lenses. The two parts are then put in contact as shown in figure. What is the focal length of combination?

1. $\text{Z}ero$
2. $20\text{cm}$
3. $5\text{cm}$
4. $10\text{cm}$

Q. A thin double convex lens has radii of curvature each of magnitude 40 cm and is made of glass with refractive index 1.65. Its focal length is nearly

1. 20 cm
2. 31 cm
3. 35 cm
4. 50 cm

Q. A thin double convex lens has radii of curvature each of magnitude 40 cm and is made of glass with refractive index 1.65. Its focal length is nearly

1. 20 cm
2. 31 cm
3. 35 cm
4. 50 cm

Q. A spherical surface of radius of curvature R separates air (refractive index 1.0) from glass (refractive index 1.5). The center of curvature is in the glass. A point object P placed in air is found to have a real image Q in the glass. The line PQ cuts the surface at a point Q, and PO = OQ. The distance PO is equal to

1. 5R
2. 3R
3. 2R
4. 1.5R

Q. Find the maximum magnifying power of a compound microscope having a $25\text{D}$ lens as the objective, a $5\text{D}$ lens as the eyepiece and a separation of $30\text{cm}$ between the two lenses. The least distance for clear vision is $25\text{cm}$.

1. $8.5$
2. $9.1$
3. $3.3$
4. $6.8$

Q. the radii of curvature of a convex lens are 0.04 and 0.04. its refractive index is 1.5. find its focal length

Q. A light ray is travelling through the cross-section of an optical fibre. The optical fibre is made of four different glasses, but each part has the same geometric thickness. Their respective refractive index are shown in figure. In which part of the fibre, light will take maximum time to cross?

1. Part II
2. Part I
3. Part III
4. Part IV

Q. The radii of curvature of a lens are + 20 cm and + 30 cm. The material of the lens has a refracting index 1.6. Find the focal length of the lens (a) if it is placed in air, and (b) if it is placed in water (μ = 1.33).

Q. Light is incident on a thin lens as shown in figure. The radius of curvature of both the surfaces is $R$. The focal length for this system will be

1. $\frac{{\mu }_{3}R}{{\mu }_1}$

2. $\frac{{\mu }_2}{R}{\mu }_2-{\mu }_1$
3. $\frac{{\mu }_2-{\mu }_1}{R}$
4. $\frac{{\mu }_{3}R}{{\mu }_3-{\mu }_1}$

Q. When a light ray from a rarer medium is refracted into a denser medium, its

1. Speed decreases, wavelength increases
2. Speed increases, wavelength increases
3. Speed decreases, wavelength decreases
4. Speed increases, wavelength decreases

Q. A convex lens of focal length $f$ produces a virtual image $n$ times the size of the object. Then the distance of the object from the lens is:

1. $\left(\frac{n+1}{n}\right)f$
2. $(n+1)f$
3. $(n-1)f$
4. $\left(\frac{n-1}{n}\right)f$

Q. What is the speed of light and wavelength in a medium having refractive index $\mu =1.5$, if the wavelength of light in air is $780\text{nm}$ ?

Q. The length of the compound microscope is $18\text{cm}$. If the magnifying power for the relaxed eye is 28, find the object distance for the objective lens. Focal length of the eyepiece is $4\text{cm}$ and $D=25\text{cm}$.

1. $2.75\text{cm}$
2. $3.75\text{cm}$
3. $2.50\text{cm}$
4. $3.12\text{cm}$

Q. While calculating the focal length of a lens formula; what is different when the lens is immersed in or surrounded by some other medium than that of air?

1. ${\mu }_1$
2. ${\mu }_2$
3. $R_1\&R_2$
4. $Noneofthese$