Q: The focal length of a lens of refractive index \$\mu \$ is \$f\$. If the lens is immersed in a liquid of refractive index \$\mu \$ then the focal length of lens is

\$\dfrac{1}{f} = (n-1) (\dfrac{1}{R_1}- \dfrac{1}{R_2})\$ where, \$n\$ is refractive index of lens material with respect to its surrounding mediumIf lens is immersed in the liquid of refractive index equal to its own then \$n=1\$ and hence above equation becomes: \$\dfrac{1}{f} = 0\$\$\Rightarrow f = \infty\$

Q: A convex glass lens is immersed in water. Compared to the power in air, its power in water will :

Power of a lens \$=\dfrac{1}{f}\$Where \$f \$ is the focal length of the lens.So, by lens maker formula\$\dfrac{1}{f}=\left ( \dfrac{\mu _{2}}{\mu _{1}}-1 \right )\left ( \dfrac{1}{R_{1}}-\dfrac{1}{R_{2}} \right )\$As lens is dipped in water, \$\mu\$ of the medium is increased from 1 to \$\dfrac{4}{3} \$ (i.e. refractive index of water), so, \$\dfrac{\mu_{2}}{\mu_{1}}\$ term decreases, so, \$\left ( \dfrac{\mu_{2}}{\mu_{1}}-1 \right )\$ term decrease which leads to decrease of \$\dfrac{1}{f}.\$ so, power \$\left ( =\dfrac{1}{f} \right )\$ decreases.

Question 1

An achromatic combination of lenses produce :

Accepted Answer

An achromatic combination of lenses provide deviation without dispersion. So, images are unaffected by variation of refractive index with wavelength. Hence correct option is C.

Question 2

An experiment is performed to find the refractive index of glass using a travelling microscope. In this experiment distances are measured by:

Accepted Answer

The travelling microscope moves horizontally on a main scale provided with the vernier scale provided with the microscope that's why, In a travelling microscope to find the refractive index of glass we measure distance by a vernier scale provided on the microscope.

Question 3

The focal length of a lens of refractive index $\mu $ is $f$. If the lens is immersed in a liquid of refractive index $\mu $ then the focal length of lens is

Accepted Answer

$\dfrac{1}{f} = (n-1) (\dfrac{1}{R_1}- \dfrac{1}{R_2})$ where, $n$ is refractive index of lens material with respect to its surrounding mediumIf lens is immersed in the liquid of refractive index equal to its own then $n=1$ and hence above equation becomes: $\dfrac{1}{f} = 0$$\Rightarrow f = \infty$

Question 4

The refraction of light is commonly known as :

Accepted Answer

The refraction of light is commonly known as bending.The refracted rays bend towards the normal when they enter from rarer to denser medium.The refracted rays bend away from the normal when they enter from denser to rarer medium.

Question 5

A glass slab is placed in the path of beam of convergent light. The point of convergence of light

Accepted Answer

As a glass has refractive index of 3/2 with respect to air, the convergent light will bend towards the normal in the glass and again bend away from the normal, but in the whole process the beam is displaced parallel to initial path as shown in figure and converge at a greater distance from the glass slab.

Question 6

What are the colours of the Sun observed most during sunrise/sunset and noon?

Accepted Answer

During sunrise and sunset the sun rays have to pass through a larger distance and also a greater thickness of air since it is low in the sky. At these positions, the sky looks orange-red colour because photons of red and orange light are least scattered through the atmosphere and are able to reach our eyes.

Question 7

Red light is used as danger signal because it is:

Accepted Answer

Red light is used as danger signal because it is having high wavelength, less scattering ,hence can travel larger distances.

Question 8

The line joining the pole and the centre of curvature of a mirror is called the :

Accepted Answer

The line joining the pole and the center of curvature of a mirror is called the principal axis.

Question 9

Blue colour of  sky is due to:

Accepted Answer

Blue light is scattered the most. Hence, as sunlight travels the earth, most of the blue colour is scattered and hence spread. This causes the sky to appear blue in the day.

Question 10

A convex glass lens is immersed in water. Compared to the power in air, its power in water will :

Accepted Answer

Power of a lens $=\dfrac{1}{f}$Where $f $ is the focal length of the lens.So, by lens maker formula$\dfrac{1}{f}=\left ( \dfrac{\mu _{2}}{\mu _{1}}-1 \right )\left ( \dfrac{1}{R_{1}}-\dfrac{1}{R_{2}} \right )$As lens is dipped in water, $\mu$ of the medium is increased from 1 to $\dfrac{4}{3} $ (i.e. refractive index of water), so, $\dfrac{\mu_{2}}{\mu_{1}}$ term decreases, so, $\left ( \dfrac{\mu_{2}}{\mu_{1}}-1 \right )$ term decrease which leads to decrease of $\dfrac{1}{f}.$ so, power $\left ( =\dfrac{1}{f} \right )$ decreases.

Ray Optics And Optical Instruments

Physics
9817 Views

An achromatic combination of lenses produce :

An experiment is performed to find the refractive index of glass using a travelling microscope. In this experiment distances are measured by:

The focal length of a lens of refractive index $μ$ is $f$ . If the lens is immersed in a liquid of refractive index $μ$ then the focal length of lens is

The refraction of light is commonly known as :

A glass slab is placed in the path of beam of convergent light. The point of convergence of light

What are the colours of the Sun observed most during sunrise/sunset and noon?

Red light is used as danger signal because it is:

The line joining the pole and the centre of curvature of a mirror is called the :

Blue colour of sky is due to:

A convex glass lens is immersed in water. Compared to the power in air, its power in water will :

Ray Optics And Optical Instruments

Physics 9817 Views

An achromatic combination of lenses produce :

An experiment is performed to find the refractive index of glass using a travelling microscope. In this experiment distances are measured by:

The focal length of a lens of refractive index μ is f. If the lens is immersed in a liquid of refractive index μ then the focal length of lens is

The refraction of light is commonly known as :

A glass slab is placed in the path of beam of convergent light. The point of convergence of light

What are the colours of the Sun observed most during sunrise/sunset and noon?

Red light is used as danger signal because it is:

The line joining the pole and the centre of curvature of a mirror is called the :

Blue colour of sky is due to:

A convex glass lens is immersed in water. Compared to the power in air, its power in water will :

Physics
9817 Views

The focal length of a lens of refractive index $μ$ is $f$ . If the lens is immersed in a liquid of refractive index $μ$ then the focal length of lens is