A concave mirror of focal length f produces an image n times the size of object. If image is real, then distance of object from mirror, is

(n – 1) f
{ (n – 1)/n} f
{(n + 1)/n} f
(n + 1) f

Solution

A convex mirror of focal length f produces an image(1/n)th of the size of the object. The distance of the object from the mirror is

(n – 1) f
f/n
(n +1) f
nf

Solution

Light travels through a glass plate of thickness t and having refractive index μ. If c be the velocity of light in vacuum, the time taken by the light to travel this thickness of glass is

\(\frac{t}{\mu c}\)
tμc
\(\frac{\mu t}{c}\)
\(\frac{tc}{\mu }\)

Solution

A vessel of depth 2d cm is half filled with a liquid of refractive index μ₁ and the upper half with a liquid of refractive index μ₂. The apparent depth of the vessel seen perpendicularly is

\(\left ( \frac{\mu _{1}\mu _{2}}{\mu _{1}+\mu _{2}} \right )d\)
\(\left ( \frac{1}{\mu _{1}}+\frac{1}{\mu _{2}} \right )d\)
\(\left ( \frac{1}{\mu _{1}}+\frac{1}{\mu _{2}} \right )2d\)
\(\left ( \frac{1}{\mu _{1}\mu _{2}}\right )2d\)

Solution

Apparent depth = d/μ₁+ d/μ₂

Monochromatic light of wavelength λ₁ travelling in a medium of refractive index μ₁ enters a denser medium of refractive index μ₂. The wavelength in the second medium is

λ₁ (μ₁/μ₂)
λ₁ (μ₂/μ₁)
λ₁ (μ₂– μ₁)/μ₂
λ₁ (μ₂– μ₁)/μ₁

Solution

The critical angle for light going from medium X into medium Y is θ. The speed of light in medium X is v, then speed of light in medium Y is

v(1 – cos θ)
v/sin θ
v/cosθ
v cos θ

Wavelength of light used in an optical instrument are λ₁= 4000 Å and λ₂ = 5000 Å, then ratio of their respective resolving powers(corresponding to λ₁ and λ₂) is

16 : 25
9 : 1
4 : 5
5 : 4

Solution

If two mirrors are kept at 60º to each other,then the number of images formed by them is

Solution

An electric bulb illuminates a plane surface. The intensity of illumination on the surface at a point 2 m away from the bulb is 5 × 10^–4 phot (lumen/cm²). The line joining the bulb to the point makes an angle of 60º with the normal to the surface. The luminous intensity of the bulb in can dela(candle power) is

40√3
40
20
40 × 10^-4

Solution

A lamp of 250 candlepower is hanging at a distance of 6 m from a wall. The illuminance at a point on the wall at a minimum distance from lamp will be

9.64 lux
4.69 lux
6.94 lux
None of these

Solution

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