Ray optics practice · Medium

Which one of the following statements concerning spherical mirrors is correct?

The focal lengths for violet, green and red light rays are ${f_V},\,\,{f_G}$ and ${f_R}$ respectively. Which of the following is the true relationship

Assertion : Sky appears blue.

Reason : Sensitivity of eye is higher for yellow color as compare to violet colour.

Optical fibres are related with

The focal length $f$ is related to the radius of curvature $r$ of the spherical convex mirror by

Assertion: Diamond glitters brilliantly.
Reason: Diamond does not absorb sunlight.

Given below are two statements
Statement-I: The telescope that uses a lens as an objective is called "refracting telescope"
Statement-II: The telescope that uses a mirror as an objective is called "reflecting telescope

The two surfaces of a biconvex lens has same radii of curvatures. This lens is made of glass of refractive index $\mathrm{1}\mathrm{.5}$ and has a focal length $\mathrm{10}\,\,\mathrm{cm}$ in air. The lens is cut into two equal halves along a plane perpendicular to its principle axis to yield two plano-convex lenses. The two pieces are glued such that the convex surfaces touch each other. If this combination lens is immersed in water (refractive index $\mathrm{ = 4}\,\mathrm{/}\,\mathrm{3}$), its focal length (in cm) is

A signal of 100 THz frequency can be transmitted with maximum efficiency by:

Assertion : In optical fibre, the diameter of the core is kept small.
Reason : This smaller diameter of the core ensures that the fibre should have incident angle more than the critical angle required for total internal reflection.

Consider an extended object immersed in water contained in a plane trough.
When the object is seen close to the edge of the trough, then the object looked distorted because,

Image of an object approaching a convex mirror of radius of curvature $\mathrm{20}\,\,\mathrm{m}$ along its optical axis is observed to move from $\frac{{25}}{3}\,\,\mathrm{m}$ to $\frac{{50}}{7}\,\,\mathrm{m}$ in $\mathrm{30 s}$. What is the speed of the object in $\mathrm{kmh}{\,^{ - 1}}$ ?

Statement-A: A lens has low principal focal lengths which may differ.

Statement-B: Light can fall on either surface of the lens. The two principal focal lengths differ when medium on the two sides have different refractive indices.

A satisfactory photographic print is obtained when the exposure time is $10\,\,s$ at a distance of $2\,\,m$ from a $60\,\,cd$ lamp. The time of exposure required for the same quality print at a distance of $4\,\,m$ from a $120\,\,cd$ lamp is

An object and a screen are kept at a distance of $120 \mathrm{~cm}$. A lens is kept between them so that a real image is formed on the screen for two different positions of the lens. Difference between the positions of the lens is $60 \mathrm{~cm}$. The focal length of the lens is

A lamp is hanging $1\,\,m$ above the centre of a circular table of diameter $1\,\,m$. The ratio of illuminaces at the centre and the edge is

Real image can be obtained from

An object is placed (i) $10 \mathrm{~cm}$, (ii) $5 \mathrm{~cm}$ in front of a concave mirror of radius of curvature $15 \mathrm{~cm}$. Find the position, nature and magnification of the image in each case.

A man can see the objects upto a distance of one metre from his eyes. For correcting his eye sight so that he can see an object at infinity, he requires a lens whose power is
Or
A man can see upto $100\,\,cm$ of the distant object. The power of the lens required to see far objects will be

A prism of refractive index $\sqrt 2$ has a refracting angle of $60^\circ .$ At what angle a ray must be incident on it so that it suffers a minimum deviation?

If the wavelength of light in vacuum be $\lambda$, the wavelength in a medium of refractive index $n$ will be

A glass slab of thickness $8\;cm$ contains the same number of waves as $10\;cm$ of water when both are transverse by the same monochromatic light. If the refractive index of water is 4/3, then refractive index of glass is

The number of lenses in a terrestrial telescope is

An astronomical, refracting telescope will have large angular magnification and high angular resolution, when it has

an objective lens of

A compound microscope is of magnifying power 100. The magnifying power of its eye piece is 4. Find the magnification of its objective.

A candle is placed before a thick plane mirror. When looked obliquely in the mirror, a number of images are seen from the surfaces of the plane mirror. Then

Assertion: The focal length of lens does not change when red light is replaced by blue light.

Reason: The focal length of lens does not depends upon colour of the light used.

The phenomenon by which light travels in an optical fibres is

Which mirror is to be used to obtain a parallel beam of light from a small lamp?

Assertion: The stars twinkle while the planets do not.

Reason: The stars are much bigger in size than the planets.