Ray optics practice · Medium

For finding out focal length of a convex lens
using two needles by parallax method, object and
image needles are 25 cm apart. If focal length of
lens is found 6 cm then possible values of object
needle distance from lens are:

Ability of the eye to see objects at all distances is called

Rising and setting sun appears to be reddish because

The maximum magnification that can be obtained with a convex lens of focal length $2.5\,\,cm$ is (the least distance of distinct vision is $25\,\,cm$)

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

When white light passes through a glass prism, one gets spectrum on the other side of the prism. In the emergent beam, the ray which is deviating least is
or
Deviation by a prism is lowest for

Assertion: There is no dispersion of light refracted through a rectangular glass slab.

Reason: Dispersion of light is the phenomenon of splitting of a beam of white light into its constituent colour.

A medium bounded by the planes $x=0, x=a, y=b, y=-b, z=c$ and $z=0$ has refractive index $\mu(x, z)=A z^3-B x+2$. A ray of light travelling along positive $z$-axis enters the medium $B$ at point $P\left(\frac{1}{B}, 0\right)$. Then the optical path introduced by the medium (when the light ray emerges out) will be:

In human eye the focussing is done by

Select the correct statement about rainbow.

The magnifying power of a telescope is high, if

A dentist has a small mirror of focal length $\mathrm{16}\,\,\mathrm{mm}$. He views the cavity in the tooth of a patient by holding the mirror at a distance of $\mathrm{8 mm}$ from the cavity. The magnification is

In a reflecting telescope, a secondary mirror is used to:

A myopic person having far point 80 cm uses spectacles
of power −1.0 D. How far can he see clearly?

Which colour of the light has the longest wavelength?

The ratio of angle of minimum deviation for a thin prism in respect to air and when it is dipped in water will be

$\left({ }_a \mu_g=\frac{3}{2} ; { }_a \mu_w=\frac{4}{3}\right)$

Three prisms of crown glass, each have angle of prism $9^\circ$ and two prisms of flint glass are used to make direct vision spectroscope. What will be the angle of flint glass prisms if $\mu$ for flint is $\mathrm{1}\mathrm{.60}$ and $\mu$ for crown glass is $\mathrm{1}\mathrm{.53}$

Myopia is due to

The wavelength of light diminishes $\mu$ times ($\mu = 1.33$ for water) in a medium. A diver from inside water looks at an object whose natural colour is green. He sees the object as

For a colour of light the wavelength for air is $6000\;\,\mathop \mathrm{A}\limits^ \circ$ and in water the wavelength is $4500\;\,\mathop \mathrm{A}\limits^ \circ$. Then the speed of light in water will be

Assertion: If the angles of the base of the prism are equal, then in the position of minimum deviation, the refracted ray will pass parallel to the base of prism.

Reason: In the case of minimum deviation, the angle of incidence is equal to the angle of emergence.

When white light passes through the achromatic combination of prisms, then what is observed

The ratio of angle of minimum deviation of a prism in air and when dipped in water will be$({\,_a}{\mu _g} = 3/2$ and $_a{\mu _\omega } = 4/3)$

Refractive index for a material for infrared light is

Assertion (A): Formation of mirages in hot deserts is a phenomenon of total internal reflection.

Reason (R): Air close to the land is hotter than the air far from the land in a hot desert. So total internal reflection takes place.

The total distance travelled by light in one year is known as

In a converging lens as a magnifying glass, the object must be placed

If in denser medium, incidence angle is equal to critical angle, then refraction angle will be

Which of the following spectrum have all the frequencies from high to low frequency range

The minimum required size of plane mirror to visualize complete image of an object is