Physics: Topic-wise Test- 7 - NEET MCQ

The angle subtended at the eye by the top of the tower with respect to the ground is 45 degrees. This happens when the height of the tower is equal to the distance from the eye. The eye is assumed to be very near to the mirror. (Refer below figure).
Angle subtended by AB = 90 degrees/2 = 45 degrees.
Therefore, tanθ=h/60​. That is, tan45=h/60​.So, h=60m.
Hence, the height of the tower is 60 m.

The light from man M₁​ hits the mirror and then reaches the man M_2​. The positions of the moving man need to be found when the light from him hits the corners of the mirror to reach the standing man.
From geometry,
AO′=L/2​+2(L/2​)
=3L/2
​Similarly, BO′=(3L/2​)+2(3L/2​)
=9L/2
Hence AB=(9L/2)-(3L/2)=3/2
Time taken to cover this distance=3L/u​
Similarly time taken to cover CD=3L/u​
Thus total time he is visible is 6L/u​
 

A concave mirror can form both real and virtual images depending upon the distance between object and mirror.

A convex mirror can only form virtual, erect, and diminished images; therefore, it is true that it can never form a real image of a real object. 

-Virtual image cannot be formed from a virtual object.
- When an object is placed between pole and focus, the image formed by the concave mirror is magnified, virtual and erect.
-When an object is placed beyond the centre of curvature , image of it is formed between centre of curvature and focus which is diminished,real and inverted,so real image of real object can be formed by concave mirror.
-When the object is virtual, the image formed is real for the concave surface as shown in figure.

P_eq=2P_L1+2P_L2+P_M
=(2/fL1)+2(1/f_L2)-(1/f_M)
P_eq=-2(1/12)+(4/45)-(2/-15)
Peq=1/18
-1/f=1/18
F=-18cm
Here the system acts as a concave mirror.

There form 3 images due to refraction on two different lenses 3 times one upper ,1 refraction from both lenses, 1 at the bottom.
now focus of Plano concave =f=R/(1−μ)
hence focus for diagram ii> f=R/2(1−μ)
and same focus for diagram iii>because again there is combination of two two Plano concave lens
so, the ratio of focus is 1:1
 

Refraction of light of different wavelength is shown in the figure.The light inside the slab clearly splits up into different colors. The emergent ray from a single white ray is a beam of different colors, parallel to the incident ray. However the emergent beam is white, because the white rays adjacent to the incident white ray above also split into different colors that add up to these wavelengths to produce a white beam of light parallel to the incident white beam.

We can either have deviation or not and same for dispersion as only μ is different and angle of prism is of our choice
option A,B,C are correct.

(μ/v)- (μ/u) = (μ₂- μ1)/R
Or, (μ/2R) + (1/2R) = μ-1/R
Or, (μ/2) + (1/2) = (μ-1)/1
Or, (Μ+1)/2= μ-1
Or, μ+1=2μ-2
 μ=3

 

From the symmetry of the fig.ray inside the sphere is parallel to the principal axis. Taking refraction at A
(μ₂/v)−(μ₁/u))=(μ₂−μ₁)/R
(μ/∞)−(1/−R)=(μ−1)/R
(1/R)=(μ−1)/R⇒μ−1=1
μ=2

a) At first the height of the liquid level is obviously dependent because the normal shift will happen according to the depth of the liquid. 
Drawing a ray diagram keeping a coin at very deep and another close to the surface.We will notice that the earlier one will have a noticeable change of position but the later one will only change a bit. 
b) The position of the slab is independent because wherever we keep it the incident ray & the emergent ray at last will be parallel (same medium keeping in mind).
 

Given that,
The distance of object from plane mirror D=100cm
So, initial distance of image and object
=100−(−100)
=200cm
Now, object approaches the mirror with the speed=v=5cm/s  
So, distance travelled by object in 6 sec
D=5×6
D=30cm
At this instant,
Distance between mirror and object
D=100−30
D=70cm
Now, the distance between image and object is
D=70−(−70)
D=140cm
Hence, the distance between the object and its image is 140 cm.
 

The number of images formed when two mirrors are inclined to each other is given by :
n=(360/θ -1)
here θ= 90°[since walls are perpendicular]
so, number of images=n=360/90-1
=4-1
=3
These 3 images are formed by a combination of two adjacent walls with the object itself acts as objects for the ceiling mirror. So totally 4 images are formed.
Hence total number of images formed are 4+3= 7
 

Paraxial rays are ones which originate from a point source and make a small angle with the principal axis. After reflection, they give a point image, either real or virtual.
But if rays from point source that are far from the mirror axis, gives a blurred image, an effect called spherical aberration.

Given: A concave mirror of radius of curvature 20cm forms image of the sun. The diameter of the sun subtends an angle 1o on the earth. 

To find the diameter of the image

Solution:

As sun is more far from the earth,

Then we take u = infinite

Radius of curvature, R=−20cm

Focal length,

From the mirror formula

d = π/18

Distance between the slits, d=0.28×10−3 m

Distance between the slits and the screen, D=1.4m

Distance between the central fringe and the fourth (n=4) fringe, 

u=1.2×10−2 m

In case of a constructive interference, we have the relation for the distance between the two fringes as:

u=nλD/d

⇒λ=ud/nD=6×10−7m=600nm

Diffraction is defined as the process by which a beam of light or other system of waves is spread out as a result of passing through a narrow aperture or across an edge, typically accompanied by interference between the waveforms produced.

Plane. The shape of the wavefront in case of a light emerging out of a convex lens when a point source is placed at its focus is a parallel grid.

We know that,
Wavelength of light in a material:
λ= λ₀/n
where, λ=wavelength of material, λ₀=wavelength of light in vacuum,
n=index of refraction of material.
So, 650x10^-9m/1.47=442.177nm.

The angle of incidence = 90^∘ - 47.5^∘ = 42.5^∘
Now by snells’ laws we get 
sin r = sin 42.5^∘ / 1.66^∘
Thus we get r = 24.01^∘
Thus the angle with surface = 90^∘ -24.01^∘ = 65.99^∘

Plane (a small area on the surface of a large sphere is nearly planar). The portion of the wavefront of light from a distant star intercepted by the Earth is a plane.

The bright colors seen in an oil slick floating on water or in a sunlit soap bubble are caused by interference. The brightest colors are those that interfere constructively. This interference is between light reflected from different surfaces of a thin film; thus, the effect is known as thin film interference.

The Huygens-Fresnel principle states that every point on a wavefront is a source of wavelets. These wavelets spread out in the forward direction, at the same speed as the source wave. The new wavefront is a line tangent to all of the wavelets.
The correct answer is option B.