A car is fitted with a convex sideñview mirror of focal length 20 cm.Asecond 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
1/15 m/s
10 m/s
15 m/s
1/10 m/s
A.
1/15 m/s
In an optics experiment, with the position of the object fixed, a student varies the position of a convex lens and for each position, the screen is adjusted to get a clear image of the object. A graph between the object distance u and the image distance v, from the lens, is plotted using the same scale for the two axes. A straight line passing through the origin and making an angle of 45^{o} with the x-axis meets the experimental curve at P. The coordinates of P will be
(2f, 2f)
(f/2, f/2)
(f,f)
(4f, 4f)
A.
(2f, 2f)
It is possible when object kept at centre of curvature.
u = v
u = 2f,
v = 2f.
The diameter of the plano-convex lens is 6 cm and thickness at the centre is 3 mm. If speed of light in material of lens is 2 × 10^{8} m/s, the focal length of the lens is
15 cm
20 cm
30 cm
10 cm
C.
30 cm
The angle of incidence at which reflected light totally polarized for reflection from air to glass (refractive index n), is
sin^{−1} (n
sin^{−1} (1/n)
tan^{−1} (1/n)
tan^{−1} (n)
D.
tan^{−1} (n)
Brewster’s law: According to this law the ordinary light is completely polarised in the plane of incidence when it gets reflected from transparent medium at a particular angle known as the angle of polarisation. n = tan ip.
Two lenses of power -15D and +5D are in contact with each other. The focal length of the combination is
-20 cm
-10 cm
+20 cm
+10 cm
B.
-10 cm
P = P_{1} + P_{2} = −10
f= 1/P
= 0.1 m
= -10 cm
An experiment is performed to find the refractive index of glass using a travelling microscope. In this experiment distance are measured by
a vernier scale provided on the microscope
a standard laboratory scale
a meter scale provided on the microscope
a screw gauage provided on the microscope
A.
a vernier scale provided on the microscope
A plane convex lens of refractive index 1.5 and radius of curvature 30 cm is silvered at the curved surface. Now this lens has been used to form the image of an object. At what distance from this lens an object be placed in order to have a real image of the size of the object?
20 cm
30 cm
60 cm
80 cm
A.
20 cm
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 1cm thick, of refractive index 1.50 is interposed between lens and film with its plane faces parallel to film. At what distance (from lens) should object be shifted to be in sharp focus on film?
7.2 m
2.4 m
3.2 m
5.6 m
D.
5.6 m
Case I: u = –240cm, v = 12, by Lens formula
Let the xz-plane be the boundary between two transparent media. Medium 1 in z ≥ 0 has a refractive index of √2 and medium 2 with z<0 has a refractive index of √3. A ray of light in medium 1 given by the vector is incident on the plane of separation. The angle of refraction in medium 2 is
45°
60°
75°
30°
A.
45°
As a refractive index for z>0 and z≤0 is different xy-plane should be the boundary between two media.
Angle of incidence,
A student measures the focal length of the convex lens by putting an object pin at a distance ‘u’ from the lens and measuring the distance ‘v’ of the image pin. The graph between ‘u’ and ‘v’ plotted by the student should look like
C.