JEE Main Physics - Optics
Exam Duration: 60 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
Choose the CORRECT statement:
- (a)
(a) Two mirrors are inclined at an angle 450. An object is placed between them. Then the number of images is 7.
- (b)
(b) Two mirrors are inclined at an angle of 720. An object is placed between then symmetrically. The number of images is 4.
- (c)
(c) Two mirrors are inclined at an angle of 720. An object is placed unsymmetrically in between the mirrors. The number of images formed is 5.
- (d)
(d) All of the statemenrs are correct.
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
A lens behaves as a convergent lens in air and a diverging lens in water. The refractive index of the material of lens is
- (a)
equal to unity
- (b)
equal to 4/3
- (c)
between unity and 4/3
- (d)
greater than 4/3
A double convex air bubble in water will behave as
- (a)
convergent lens
- (b)
divergent lens
- (c)
plane glass slab
- (d)
concave mirror
Diametre of aplan0-convex lens is 5 cm and thickness at the center is 2.5 mm. If the speed of light in the material of the lens is 2X108ms-1, the focal length of the lens is
- (a)
15 cm
- (b)
20 cm
- (c)
25 cm
- (d)
30 cm
An air bubble in a glass slab (\(\mu \)=1.5) is 5 cm deep when viewed from one face and 2 cm deep when viewed from one face and 2 cm deep when viewed from the opposite face. The thickness of the slab is
- (a)
10.5 cm
- (b)
7 cm
- (c)
10 cm
- (d)
7.5 cm
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)
\(\frac { n-m }{ xn } \)
A prism of angle A has one surface silvered. Light rays falling at an angle of incidence 2A on first surface return back through the same path after suffering reflection at second silvered surface. Refractive index of material is
- (a)
2 sin A
- (b)
2 cos A
- (c)
\(\frac { 1 }{ 2 } \)cos A
- (d)
tan A
The retracting angle of a prism A is small. The correct statement for the dispersive power of a prism is that dispersive power.
- (a)
depends upon the material of prism
- (b)
depends upon both material and angle of prism
- (c)
depends only upon refracting angle of prism
- (d)
in small for all colours of white light
Green light of wavelength 5460 \(\mathring { A } \) is incident on an air-glass interface. If the refractive index of glass is 1.5, the wavelength of light in glass would be (c=3X108ms-1)
- (a)
3640\(\mathring { A } \)
- (b)
5460\(\mathring { A } \)
- (c)
4861\(\mathring { A } \)
- (d)
NONE OF THESE
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
The dispersive power of material of a lens of focal length 25 cm is 0.05. The longitudinal chromatic aberration of the lens is
- (a)
0.05 cm
- (b)
0.2X10-2 cm
- (c)
1.25 cm
- (d)
12.5 cm
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
In order to increase the magnifying powr of a compound microscope
- (a)
the focal lengths of objective and eyepiece should be small
- (b)
objective should have small focal length and eyepiece should have large focal length
- (c)
both should have large focal lengths
- (d)
both should have same focal length
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)
\(\sqrt { { x }_{ 1 }{ x }_{ 2 } } \)
If h1 and h2 are the heigths of the images in conjugate position of a convex lens, then the height of the object is
- (a)
\({ h }_{ 1 }+{ h }_{ 2 }\)
- (b)
\({ h }_{ 1 }-{ h }_{ 2 }\)
- (c)
\(\sqrt { { h }_{ 1 }{ h }_{ 2 } } \)
- (d)
\({ h }_{ 1 }/{ h }_{ 2 }\)
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
The apparent depth of water in cylindrical water tank of diameter 2R cm is reducing at the rate of X cm/min when water is being drained out at a constant rate. The amount of water drained in cc/min is (n1 = refractive index of air, n2 = refractive index of water)
- (a)
\(\frac { x\pi { R }^{ 2 }{ n }_{ 1 } }{ { n }_{ 2 } } \quad \)
- (b)
\(\frac { x\pi { R }^{ 2 }{ n }_{ 2 } }{ { n }_{ 1 } } \quad \)
- (c)
\(\frac { 2\pi { R }{ n }_{ 1 } }{ { n }_{ 2 } } \quad \)
- (d)
\(\pi { R }^{ 2 }x\)
An equilateral prism deviates a ray through 45° for the two angles of incidence differing by 20°. The angle of incidence, if the angle of prism is 60°, is
- (a)
62.5°
- (b)
42.5°
- (c)
Both (a) and (b) are correct
- (d)
Both (a) and (b) are wrong
A thin convex lens made from crown glass \(\left( \mu =\frac { 3 }{ 2 } \right) \)has focal length f. When it is measured in two different liquids having refractive indices \(\frac { 4 }{ 3 } and\quad \frac { 5 }{ 3 } \).It has the focal lengths f1 and f2 respectively. The correct relation between the focal length is
- (a)
f1 = f2 < f
- (b)
f1 > f and f2 becomes negative
- (c)
f2 > f and f1 becomes negative
- (d)
f1 and f2 both become negative
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
Two lenses of power - 15D and + 5D are in contact with each other. The focal length of the combination is
- (a)
- 20 cm
- (b)
- 10 cm
- (c)
+ 20 cm
- (d)
+ 10 cm