Ray optics practice · Medium

Two thin convex lenses of focal lengths $f_1$ and $f_2$ are placed at a distance $d.$ For the power of the combination to be zero, then separation $d$ should be equal is:

Show that the angle of minimum deviation produced by a thin prism is reduced to one-fourth (with respect to air) when it is immersed in water. Given ${ }^a \mu_g=3 / 2$ and ${ }^a \mu_w=4 / 3$.

A plano convex lens is made of glass of refractive index $\mathrm{1}\mathrm{.5}$. The radius of curvature of its convex surface is R. Its focal length is

Assertion : When we see the image in water, blurred image is seen.

Reason : Refractive index of air and water are different.

The relation between the linear magnification $m$, the object distance $u$ and the focal length $f$ is

A professor reads a greeting card received on his 50th birthday with $+2.5\,\mathrm{D}$ glasses keeping the card $25 \mathrm{~cm}$ away. Ten years later, he reads his farewell letter with the same glasses but he has to keep the letter $50 \mathrm{~cm}$ away. What power of lens should he now use?

Under which of the following conditions will a convex mirror of focal length $f$ produce an image that is erect, diminished and virtual

An object $2.4\,m$ in front of a lens forms a sharp image on a film $12\,\,cm$ behind the lens. A glass plate $1\,\,cm$ thick, of refractive index $\mathrm{1}\mathrm{.50}$ is interposed between lens and film with its plane faces parallel to film. At what distance (from lens) should object shifted to be in sharp focus on film

Statement(A) : The Sun is visible a little
before the actual sunrise and until a little
after the actual sunset due to refraction of
light through the atmosphere.

Statement(B) : Mass density of
'Turpentine' is less than that of water but its
optical density is higher.

Assertion: An object is placed at a distance of $f$ from a convex mirror of focal length $f$ its image will form at infinity.
Reason: The distance of image in convex mirror can never be infinity.
In above question a statement of assertion is followed by statement of reason mark the correct choice.

The cladding material of optical fibre has refractive index

Continuous emission spectrum is produced by

Assertion: A plane mirror reflects a beam of light to form a real image for real object.

Reason: The incidence beam should be convergent to form real image.

A ray of light is incident at an angle of incidence of $60^{\circ}$ on the face of a prism having prism angle of $30^{\circ}$. The ray emerging out of the prism makes an angle of $30^{\circ}$ with the incident ray. The refractive index of material of prism is

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

If the focal length of the objective lens is increased then

If the focal length of a double convex lens for red light is ${f_R}$, its focal length for the violet light is

For a compound microscope, the focal lengths of object lens and eye lens are ${f_0}$ and ${f_e}$ respectively, then magnification will be done by microscope when

Assertion : Refractive index of cold air is greater then that of hot air.

Reason : The molecules of cold air have lower thermal velocity.

A lens of large focal length and large aperture is best suited as an objective of an astronomical telescope since

Assertion: The setting sun appears to be red.

Reason: Scattering of light is directly proportional to the wave length.

When a glass lens with $n = 1.47$ is immersed in a trough of liquid, it looks to be disappeared. The liquid in the trough could be

What causes chromatic aberration?

Assertion: Just before setting, the sun may appear to be elliptical. This happens due to refraction.

Reason: Refraction of light ray through the atmosphere may cause different magnification in mutually perpendicular directions.

A plane wave of sound travelling in air is incident upon a plane water surface. The angle of incidence is $60^{\circ}$. If velocity of sound in air and water are $330 \mathrm{~m} / \mathrm{s}$ and $1400 \mathrm{~m} / \mathrm{s}$, then the wave undergoes

Assertion: In ionospheric reflection, phase change does not occurs with the light wave.
Reason: The ionosphere reflection is similar to the total internal reflection which is similar to the total internal reflection in miraj

A convex lens is immersed in a liquid, whose refractive index is equal to the refractive index of the material of the lens. Then its focal length will

How does the angle of minimum deviation of a glass prism vary, if the incident violet light is replaced with red light?

The frequency of a light ray is $6\,\, \times \,\,{10^{14}}\,\,Hz$. Its frequency when it propagates in a medium of refractive index $\mathrm{1}\mathrm{.5}$, will be

Two thin lens have a combined power of $10 \mathrm{D}$ in contact. When separated by $20 \mathrm{~cm}$ their equivalent power is $6.25 \mathrm{D}$. Find their in dividual powers in dioptres -