Physics - Optics
Exam Duration: 45 Mins Total Questions : 30
Light was falling on a surface at an angle of 450. The surface is lifted so that light now falls at an angle of 600. How is the illuminance affected?
- (a)
no effect
- (b)
\(2\sqrt { 2 } \) times
- (c)
\(\sqrt { 2 } \) times
- (d)
\(\frac { 1 }{ \sqrt { 2 } } \) times
A plane mirror produces a magnification of
- (a)
-1
- (b)
+1
- (c)
zero
- (d)
between 0 and \(\infty \)
A concave mirror of focal length f(in air) is immersed in water (\(\mu \)=4/3). The focal length of the mirror in water will be
- (a)
f
- (b)
(4/3)f
- (c)
(3/4)f
- (d)
(7/3)f
All the following statements are correct except
- (a)
The magnification produced by a convex mirror is always less than one
- (b)
A virtual, erect, same-sized image can be obtained by using a plane mirror
- (c)
A virtual, erect, magnified image can be obtained by using concave mirror
- (d)
A beam of light incident on a plane mirror always forms a virtual image. [ A real image cannot be obtained by using a plane mirror]
A thin lens has focal length f and its aperture has radius r. It forms an image of intensity I. Now the central part of the aperture upto radius r/2 is blocked by an opaque material. Then the focal length and the intensity of the image will be
- (a)
\(\frac { f }{ 2 } and\frac { I }{ 2 } \)
- (b)
\( { f }{ } and\frac { I }{ 4} \)
- (c)
\(\frac {3 f }{ 4 } and\frac { I }{ 2 } \)
- (d)
\( { f }{ } and\frac { 3I }{ 2 } \)
The focal length of the convex lens depends upon
- (a)
frquency of the light ray
- (b)
wavelength of the light ray
- (c)
both of (a) and (b)
- (d)
NONE OF THESE
Focal length of a convex lens will be maximum for
- (a)
blue light
- (b)
yellow light
- (c)
green light
- (d)
red light
How does refractive index \(\mu _{ }\) of a material vary with respect to wavelength \(\lambda \) ? A and B are constants
- (a)
\(\mu =A+\frac { B }{ { \lambda }^{ 2 } } \)
- (b)
\(\mu =A+B{ \lambda }^{ 2 }\)
- (c)
\(\mu =A+\frac { B }{ { \lambda }^{ } } \)
- (d)
\(\mu =A+B{ \lambda }^{ }\)
A thin converging lens forms the image of a certain object magnified m times. The magnification becomes n when the lens is moved nearer to object by a distance x. Focal length of the lens is
- (a)
\(\frac { xm }{ m-n } \)
- (b)
\(\frac { x mn }{ m-1 } \)
- (c)
\(\frac { x mn }{ n-m } \)
- (d)
\(\frac { n-m }{ xn } \)
If refractive index of material of aprism with prism angle A is \(\mu =cot\frac { A }{ 2 } \), then angle of minimum deviatio will be
- (a)
1800-A
- (b)
1800-2A
- (c)
1800-3A
- (d)
1800-4A
A ray of light incident on a 600 angled prism of refractive index \(\sqrt { 2 } \) suffers minimum deviation. The angle of incidence is
- (a)
700
- (b)
00
- (c)
450
- (d)
600
A spectometer set up with a prism on its prism table is immersed in water. This will result in
- (a)
increase in the angle of minimum deviation
- (b)
no change in the angle of minimum deviation
- (c)
decrease in the angle of minimum deviation
- (d)
no change in the angle of dispersion
If a monochromatic light of yellow colour is incident on a phosphorescent material, the colour of light emitted by it is
- (a)
yellow
- (b)
nearer to yellow of the visible light spectrum
- (c)
nearer to violet in the visible light spectrum
- (d)
nearer to red in the visible light
A prism produces an angular dispersion \(\theta \) in a beam of white light. The minimum angular dispersion produces by three such prism is
- (a)
\(\theta \)
- (b)
\(2\theta \)
- (c)
\(3\theta \)
- (d)
zero
The magnifying power of telescope is 'm'. If the focal length of the piece is doubled, then its magnifying power will become
- (a)
2 m
- (b)
m/2
- (c)
\(\sqrt { 2 } \) m
- (d)
3 m
Length of a Galilean telescope in normal adjustment, in terms of the focal lengths of the objectives (f0) and that of the eye piece (fe) is
- (a)
f0-fe
- (b)
f0+fe
- (c)
f0+f0
- (d)
fe-f0
A person using a lens as a simple microscope sees an
- (a)
inverted virtual image
- (b)
inverted real magnified image
- (c)
upright virtual image
- (d)
upright real magnified image
The resolving power of a telescope depends on
- (a)
focal length of eye lens
- (b)
focal length of objective lens
- (c)
length of the telescope
- (d)
diameter of the objective lens
The resolving limit of healthy eye is about
- (a)
1'
- (b)
1''
- (c)
10
- (d)
\(\frac { 1 }{ 60 } \)''
A person cannot see objects clearly beyond 2.0 m. The power of lens required to correct his vision will be
- (a)
+2.0 dioptre
- (b)
-1.0 dioptre
- (c)
+1.0 dioptre
- (d)
-0.5 dioptre
Colour of sky appears blue because
- (a)
all blue colour of solar spectrum is obsorbed
- (b)
it is its natural colour
- (c)
blue colour of solar spectrum is scattered
- (d)
all red colour of solar spectrum is obsorbed
With a concave mirror, an object is placed at a distance X1 from the principal focus, on the principal axis. The image is formed at a distance X2 from the principal focus. The focal length of the mirror is
- (a)
\({ x }_{ 1 }{ x }_{ 2 }\)
- (b)
\(\frac { { x }_{ 1 }+{ x }_{ 2 } }{ 2 } \)
- (c)
\(\sqrt { \frac { { x }_{ 1 } }{ { x }_{ 2 } } } \)
- (d)
\(\sqrt { { x }_{ 1 }{ x }_{ 2 } } \)
A lens formed a virtual image 4 cm away from it when an object is placed 10 cm away from it. Which lens is this and what is its focal length?
- (a)
concave, 6.67 cm
- (b)
concave, 2.86 cm
- (c)
convex, 2.86 cm
- (d)
may be concave or convex, 6.67 cm
The focal length of the objective and the eyepiece of a microscope are 4 mm and 25 mm respectively. If the final image is formed at infinity and the length of the tube is 16 cm, then the magnifying power of microscope will be (object is at to)
- (a)
- 337.5
- (b)
- 3.75
- (c)
3.375
- (d)
33.75
A jar of height h is filled with a transparent liquid of refractive index \(\mu \) (figure). At the centre of the jar on the bottom surface is a dot. Find the minimum diameter of a disc, such that when placed on the top surface symmetrically about the centre, the dot is invisible.
- (a)
\(d=\frac { h }{ \sqrt { { u }^{ 2 }-1 } } \)
- (b)
\(d=\frac { 2h }{ \left( { \mu }^{ 2 }-1 \right) } \)
- (c)
\(d=\frac { 2h }{ \sqrt { \left( { \mu }^{ 2 }-1 \right) } } \)
- (d)
None of the above
A beaker contains water upto a height h1 and kerosene upto height h2 above water, so that the total height of (water + kerosene) is (h1 + h2). Refractive index of water is \({ \mu }_{ 1 }\) and that of kerosene is \({ \mu }_{ 2 }\). The apparent shift in the position of the bottom of the beaker when viewed from above is
- (a)
\(\left( 1-\frac { 1 }{ { \mu }_{ 1 } } \right) { h }_{ 2 }+\left( 1-\frac { 1 }{ { \mu }_{ 2 } } \right) { h }_{ 1 }\)
- (b)
\(\left( 1+\frac { 1 }{ { \mu }_{ 1 } } \right) { h }_{ 1 }+\left( 1+\frac { 1 }{ { \mu }_{ 2 } } \right) { h }_{ 2 }\)
- (c)
\(\left( 1-\frac { 1 }{ { \mu }_{ 1 } } \right) { h }_{ 1 }+\left( 1-\frac { 1 }{ { \mu }_{ 2 } } \right) { h }_{ 2 }\)
- (d)
\(\left( 1+\frac { 1 }{ { \mu }_{ 1 } } \right) { h }_{ 2 }-\left( 1+\frac { 1 }{ { \mu }_{ 2 } } \right) { h }_{ 1 }\)
When a monochromatic red light is used instead of blue light in a convex lens, its focal length will
- (a)
not depend on colour of light
- (b)
increase
- (c)
decrease
- (d)
remain same
A car is fitted with a convex side-view mirror of focal length 20 cm. A second car 2.8 m behind the first car is overtaking the first car at a relative speed of 15 m/s. The speed of the image of the second car as seen in the mirror of the first one is
- (a)
\(\frac{1}{15} m/s\)
- (b)
10 m/s
- (c)
15 m/s
- (d)
\(\frac{1}{10} m/s\)