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Physics NEET MCQ
Quiz 11
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Q.1
When a light ray travels into a single medium then refractive index is
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a)directly proportional to wavelength of light
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b) inversely proportional to wavelength of light
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c)inversely proportional to square of wavelength of light
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d)directly proportional to the square of wavelength of light
Explanation
Answer: (c)
Q.2
The equation for two waves obtained by two light sources are as given by y1=A1sin3ωt and y2=A2cos(3ωt + π/6). What will be the value of phase difference at time t
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a) 3π/2
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b) 2π/3
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c)π
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d)π/2
Explanation
use cosθ=sin(π/2+θ) π/2 + π/6=2π/3Answer: (b)
Q.3
The path difference between two waves y1=A1sinωt and y2cos(ωt + φ) will be
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a) (λ/2π) φ
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b) (λ/2π) (φ+ π/2)
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c)(λ/2π) (φ- π/2)
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d)(λ/2π) (φ)
Explanation
Phase difference=π/2 + φ path difference is λ for phase difference of 2π∴ option 'b' is correct Answer:(b)
Q.4
Two coherent waves are represented by y1=a1cosωt and y2=a2sinωt. The resultant intensity due to interference will be
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c) a12 + a22
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d) a12 - a22
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a) a₁ + a₂
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b) a₁ - a₂
Explanation
phase difference between both the waves is π/2 Answer: (c)
Q.5
For a double slit experiment the necessary equation representing the coherent sources are y1=10sinωt and y2=10sin(ωt - π/6) then the value of intensity of bright fringes will be
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a)20
0%
b) 400
0%
c)100
0%
d)200
Explanation
Answer: (b)
Q.6
The phenomenon of diffraction can be observed, when the obstacle is
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a) Quit large as compared to the wavelength of light used
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b) Quit small as compared to the wavelength of light used
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c)Of the same order as the wavelength of light used
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d)Bear no relation with the wavelength of light used
Explanation
Answer: (c)
Q.7
Who first discovered the phenomenon of diffraction
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a) Fresnel
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b) Fraunhofer
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c)Arago
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d)Grimaldi
Explanation
Answer:(d)
Q.8
The correct relation between the size of the obstacle and the diffraction event is
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a) a/λ=1
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b) a/λ=0
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c) a/λ=∞
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d) a/λ=150
Explanation
Answer: (a)
Q.9
The fringe width in single slit diffraction pattern is proportional to
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a)a/λ
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b) λ/a
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c)aλ
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d)λ
Explanation
Answer: (b)
Q.10
The ratio of intensities of consecutive maxima in the diffraction slit is
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a) 1:4:9
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b) 1:2:3
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c)1 : 4/9π2 : 4/25π2
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d)1: 4/π2 : 9/π2 :
Explanation
Answer: (c)
Q.11
An unpolarized beam of light is incident on a group of four polarizing sheets which are arranged in such a way that characteristic direction of each polarizing sheet makes an angle of 30° with that of the preceding sheet. The % age of incident light transmitted by first polarizer will be
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a) 100%
0%
b) 50%
0%
c) 25%
0%
d) 12.5%
Explanation
Answer: (b)
Q.12
Unpolarised light of intensity 32 Wm-2 passes through three polarizes such that the transmission axis of the last polarizer is crossed with that of the first. The intensity of final emerging light is 3W-The intensity of light transmitted by first polarizer will be
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a)32 Wm-2
0%
b) 16Wm-2
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c)8Wm-2
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d)4Wm-2
Explanation
Answer: (b)
Q.13
A beam of unpolarized light of intensity Io is passed first through another tourmaline crystal B oriented so that its principle plane is parallel to that of A. The intensity of final emergent light is I. The value of I is
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a) Io /2
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b) Io / 4
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c)Io / 8
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d)none of these
Explanation
Answer: (a)
Q.14
Two Nicols prism are oriented with their principal planes making an angle of 60°. Then the percentage of incident unpolarized light which passes through the system is
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a) 100
0%
b) 50
0%
c)12.5
0%
d)37.5
Explanation
Answer:(c)
Q.15
Out of the the following, of which colour, sensitivity of human eye is highest
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a) green
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b) red
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c) violet
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d) white
Explanation
Answer: (a)
Q.16
In Young's experiment if transparent thin sheet are placed in front of two thin slits such that the central bright fringe remains at the same position. Thickness and refractive index of both sheets are t1 and t2 and µ1 and µ2 respectively. In this case..
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a)t₁ / t₂=µ1 / µ2
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b) t₂ / t₁=µ1 / µ2
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c)t₁ / t₂=(µ2-1) / (µ1-1)
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d)t₂ / t₁=(µ2-1) / (µ1-1)
Explanation
Use formula shift=(µ - 1) tAnswer: (c)
Q.17
The ratio of resolving power of telescope, when light of wavelengths 4000Å and 5000Å are used, is
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a) 16 : 25
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b) 5:4
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c)4:5
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d)9:1
Explanation
Answer: (b)
Q.18
The diameter of the lens of telescope is 1.22 m. The wavelength of light is 5000Å. The resolving power of the telescope is ...m-1
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a) 2×105
0%
b) 2×106
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c)2×102
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d)2×104
Explanation
resolving power of telescope=D/1.22λ Answer:(b)
Q.19
Unpolarized light falls on two polarizers placed one on top the other. What must be the angle between the characteristic directions of the polarizer if the intensity of the transmitted light is one third of the incident beam
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a) 54.7°
0%
b) 35.3°
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c) 0°
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d) 60°
Explanation
When unpolarized light passes through first plate emergent ray intensity is half of the original For second plate I=Iocos2θ I/3=(I/2)cos2θ find θ Answer: (b)
Q.20
For a normal eye, the cornea of eye provides a converging power of 40 D and the least converging power of the eye lens behind the cornea is 20 D. Using this information, the distance between the retina and the cornea - eye lens can be estimated to be
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a) 5 cm
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b) 2.5 cm
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c) 1.67 cm
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d) 1.5 cm
Explanation
Total power 40+20 =60 D Image is formed at retina thus focal length = distance between retina and cornea Answer:(c)
Q.21
In Young’s double slit experiment, the slits are 2 mm apart and are illuminated by photons of two wavelengths λ1 = 12000 Å and λ2 = 10000 Å. At what minimum distance from the common central bright fringe on the screen 2 m from the slit will a bright fringe from one interference pattern coincide with a bright fringe from the other?
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a) 8 mm
0%
b) 6 mm
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c) 4 mm
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d) 3 mm
Explanation
Let n1 and n2 be the bright fringe coincide at position X on screen i.e 5th fringe of λ1 coincide with 6th fringe of λ2 Answer:(b)
Q.22
A parallel beam of fast moving electrons is incident normally on a narrow slit. A fluorescent screen is placed at a large distance from the slit. If the speed of the electrons is increased, which of the following statements is correct?…[NEET 2013]
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a) Diffraction pattern is not observed on the screen in the case of electrons
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b) The angular width of the central maximum of the diffraction pattern will increase
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c) The angular width of the central maximum will decrease
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d) The angular width of the central maximum will be unaffected
Explanation
From De Broglie hypothesis, increase is velocity of electron is decrease in wave length as λ= h/mv From the width of central maxima Thus decrease in wave length decreases the angular width Answer:(c)
Q.23
The angle of a prism is 'A'. One of its refracting surfaces is silvered. Light rays falling at an angle of incidence 2A On the first surface returns back through the same path after suffering reflection at the silvered surface. The reaction index µ,of the prism is
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a) ½cosA
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b) tanA
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c) 2sinA
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d) 2cosA
Explanation
It is given that light reflect back on same path thus angle of incidence on reflected surface is zero. Or angle r2=0 Now r1 + r2 = A r1 = A µ=2cosA Answer:(d)
Q.24
Diameter of a plano - convex lens is 6 cm and thickness at the centre is 3 mm. If speed of light in material of lens is 2 × 108 m/s, the focal length of the lens is :
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a) 15 cm
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b) 20 cm
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c) 30 cm
0%
d) 10 cm
Explanation
In problem radius of curvature not given can be calculated as follows AA’ is diameter of lens, r is the radius of curvature OA is radius, OC = r-0.3 From triangle OAC r2 = (r-0.3)2 + 32 r2 = r2 – 0.6r + 0.09 + 9 0.6r = 9.09 r= 9.09/0.6 =15.15 given velocity of light is medium is 2 × 108 m/s, so refractive index = 1.5 Now using lens formula f= 30.3 approx = 30cm Answer:(c)
Q.25
In the Young's double-silt experiment, the intensity of light at a point on the screen where the path difference is λ is K, (λ being the wavelength of light used). The intensity at a point where the path difference is λ/4,will be …
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a) K/2
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b) zero
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c) K
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d) K/4
Explanation
In double –slit experiment intensity is same of bright fringes If path difference is nλ bright fringes. For dark fringes Given path difference is λ/4 thus we have to use formula Here if path difference λ the δ = 2π I1 = I2 = I I’= 4I = K Now if path difference λ/4 then δ =2π/4=π/2 I"=2I If 4I = K then 2I = K/2 Answer:(a)
Q.26
If the focal length of objective lens is increased then magnifying power of
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a) microscope and telescope both will decrease
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b) microscope will decrease but that of telescope will increase
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c) microscope will increase but that of telescope decrease
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d) microscope and telescope both will increase
Explanation
Microscope The total magnification, when the image is formed at infinity, is Thus, the total magnification, when the image is formed at near point, is Thus increasing the focal length of objective lens magnification of microscope decreases. Telescope Thus increasing the focal length of objective lens magnification of telescope increases Answer:(b)
Q.27
In a double slit experiment, the two slits are 1 mm apart and the screen is placed 1 m away. A monochromatic light of wavelength 500 nm is used. What will be the width of each slit for obtaining ten maxima of double slit within the central maxima of single slit pattern?
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a) 0.02 mm
0%
b) 0.2 mm
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c) 0.1 mm
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d) 0.5 mm
Explanation
width of central maxima Position of 10 maxima Given width of central maximum = Position of 10th bright fringe Answer:(b)
Q.28
The refracting angle of a prism is A, and refractive index of the material of the prism is cot (A/2). The angle of minimum deviation is :
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a) 180° + 2A
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b) 180° - 3A
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c) 180° - 2A
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d) 90° – A
Explanation
Also From (i) and (ii) Dm =π-2A Answer:(c)
Q.29
Two identical thin plano-convex glass lenses (refractive index 1.5) each having radius of curvature of 20 cm are placed with their convex surfaces in contact at the centre. The intervening space is filled with oil of refractive index 1.The focal length of the combination is : … [ AIMPT 2015]
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a) 50 cm
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b) -20 cm
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c) -25 cm
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d) -50 cm
Explanation
Liquid in between two lens acts as concave lens. Combination of three lenses. Answer:(a)
Q.30
For a parallel beam of monochromatic light of wavelength ‘λ‘, diffraction is produced by a single slit whose width ‘a‘ is of the order of the wavelength of the light. If ‘D‘ is the distance of the screen from the slit, the width of the central maxima will be :
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a)
0%
b)
0%
c)
0%
d)
Explanation
Standard formula for width of central maxima Answer:(b)
Q.31
At the first minimum adjacent to the central maximum of a single slit diffraction pattern the phase difference between the Huygen鈥檚 wavelet from the edge of the slit and the wavelet from the mid point 鈥 Re AIPMT 2015]
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a) π/8 radian
0%
b) π/4 radian
0%
c) π/2 radian
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d) π radian
Explanation
From the figure path difference is 位/2 thus phase difference is 蟺 radian Answer:(d)
Q.32
Two slits in Youngs experiment have widths in the ratio 1 :The ratio of intensity at the maxima and minima in the interference pattern, Imax/Iminis :
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a) 4/9
0%
b) 9/4
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c) 121/49
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d) 49/121
Explanation
Answer:(b)
Q.33
In an astronomical telescope in normal adjustment a straight black line of length L is drawn on inside part of objective lens. The eye-piece forms a real image of this line. The length of this image is I. The magnification of the telescope is :…[ Re AIPMT 2015]
0%
a)
0%
b)
0%
c)
0%
d)
Explanation
Since real image is formed ray diagram will be Magnification (M) is ratio of image height and object height M=I/L Answer:(a)
Q.34
A beam of light consisting of red, green and blue colours is incident on a right angled prism. The refractive index of the material of the prism for the above red, green and blue wavelengths are 1.39,1.44 and 1.47, respectively. The prism will :- [ ReAIPMT 2015]
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a) separate the red colour part from the green and blue colours
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b) separate the blue colour part from the red and green colours
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c) separate all the three colours from one another
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d) not separate the three colours at all
Explanation
Angel of incidence is 45° n=1.41 more the refractive index, lesser is the critical angle. That is if angle of incidence is more than critical angle light will internally reflected Thus for any light having refractive index more than 1.41 will be totally internal reflected because critical angle is less than 45 Red light refractive index < 1.41. Thus red will pass others will totally internally reflected Answer:(a)
Q.35
The intensity at the maximum in a Young's double slit experiment is IDistance between two slits is d = 5λ, where λ is the wavelength of light used in the experiment. What will be the intensity in front of one of the slits on the screen placed at a distance D = 10 d ?[ AIPMT 2016]
0%
a) I0
0%
b) I0/4
0%
c) 3I0/4
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d) I0/2
Explanation
It is given that that maximum intensity which is 4I0 in above equation should now be treated as I0 equation changes to K=2×/λ ,δ = path difference Here x= 2.5λ and d =5λ, D= 50λ I = I0/2 Answer:(d)
Q.36
The angle of incidence for a ray of light at a refracting surface of a prism is 45° . The angle of prism is 60°. If the ray suffers minimum deviation through the prism, the angle of minimum deviation and refractive index of the material of the prism respectively, are : … [ AIPMR 2016]
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a) 45°,1/√2
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b) 30°, √2
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c) 45°, √2
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d) 30°,1/√2
Explanation
i = 45° ; A = 60°; δm = 2i – A = 30° Answer:(b)
Q.37
A astronomical telescope has objective and eyepiece of focal lengths 40 cm and 4 cm respectively. To view an object 200 cm away from the objective, the lenses must be separated by a distance :-
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a) 37.3 cm
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b) 46.0 cm
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c) 50.0 cm
0%
d) 54.0 cm
Explanation
Using lens formula for objective lens v0= 50 cm Tube length l= |v0| + fe = 50 +4 = 54 cm Answer:(d)
Q.38
Two identical glass (μg=3/2) equiconvex lenses of focal length f each are kept in contact. The space between the two lenses is filled with water (μw=4/3). The focal length of the combination is ….[NEET II -2016]
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a) 4f/3
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b) 3f/4
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c) f/3
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d) f
Explanation
Power of lenses gets added Given that both convex lenses have focal length =f Liquid between the convex lenses form concave lens Answer:(b)
Q.39
An air bubble in a glass slab with refractive index1.5 (near normal incidence) is 5 cm deep when viewed from one surface and 3 cm deep when viewed from the opposite face. The thickness (in cm) of the slab is …[ NEET II- 2016]
0%
a) 12
0%
b) 16
0%
c) 8
0%
d) 10
Explanation
ho = real depth, hi = apparent depth no= Refractive index of medium in which object is ni = Refractive index of medium in which observer is First side ho = 7.5 cm Second side h’o = 4.5 cm Thickness of slab =7.5 +4.5 = 12cm Answer:(a)
Q.40
The interference pattern is obtained with two coherent light sources of intensity ratio n. In the interference pattern, the ratio will be…[ NEET II -2016]
0%
a)
0%
b)
0%
c)
0%
d)
Explanation
nI1=I2 Answer:(d)
Q.41
A person can see clearly objects only when they lie between 50 cm and 400 cm from his eyes. In order to increase the maximum distance of distinct vision to infinity, the type and power of the correcting lens, the person has to use, will be :-
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a) concave, – 0.2 diopter
0%
b) convex, + 0.15 diopter
0%
c) convex, + 2.25 diopter
0%
d) concave, – 0.25 diopter
Explanation
As we want to correct myopia. So, far point must go to infinity. v = –4 m, u = – ∞, P = ? (–) implies concave mirror Answer:(d)
Q.42
Young’s double slit experiment is first performed in air and then in a medium other than air. It is found that 8th bright fringe in the medium lies where 5thdark fringe lies in air. The refractive index of the medium is nearly
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a) 1.25
0%
b) 1.59
0%
c) 1.69
0%
d) 1.78
Explanation
In liquid wavelength decreases given by relation nλ’ =λ …(i) Position is same or x is same for both fringes, D and d same 5thdark fringe 8th bright fringe From (i) n = 16/9 = 1.777 = 1.78 Answer:(d)
Q.43
The ratio of resolving powers of an optical microscope for two wavelengths λ1= 4000 Å and λ2= 6000 Å is …[NEET 2017]
0%
a) 8 : 27
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b) 9 : 4
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c) 3 : 2
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d) 16 : 81
Explanation
Answer:(c)
Q.44
Two Polaroids P1 and P2 are placed with their axis perpendicular to each other. Unpolarised light I0 is incident on PA third polaroid P3 is kept in between P1 and P2 such that its axis makes an angle 45° with that of PThe intensity of transmitted light through P2 is …
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a) I0/2
0%
b) I0/4
0%
c) I0/8
0%
d) I0/16
Explanation
Intensity of light passing through P1 = I0/2 Now P3 is at angle 45° with P3 thus I’ Now P4 is at angle of 45° with P3 thus I” Answer:(c)
Q.45
A beam of light from a source L is incident normally on a plane mirror fixed at a certain distance x from the source. The beam is reflected back as a spot on a scale placed just above the source L. When the mirror is rotated through a small angle θ, the spot of the light is found to move through a distance y on the scale. The angle θ is given by … [ NEET 2017]
0%
a) y/2x
0%
b) x/y
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c) x/2y
0%
d) x/y
Explanation
When the mirror is rotated by θ then angle between the incident and reflected ray 2θ. Given that angle θθ is very small, 2θ is also small, M is mirror , N is normal to mirror From geometry y = x 2θ θ=y/2x Answer:(a)
Q.46
A thin prism having refracting angle 10° is made of glass of refractive index 1.This prism is combined with another thin prism of glass of refractive index1.This combination produces dispersion without deviation. The refracting angle of second prism should be
0%
a) 4°
0%
b) 6°
0%
c) 8°
0%
d) 10°
Explanation
For small angle prism minimum deviation is given by δm = (n1 – 1) A Since combination of two prism do not produce deviation (n1 – 1) A +(n2 – 1) A’ = 0 |(1.42-1) 10| = |(1.7 – 1) A’| 4.2 =0.7 A’ Answer:(b)
Q.47
A beam of unpolarised light of intensity I0 is passed through a polaroid A and then through another polaroid B which is oriented so that its principal plane makes an angle of 45° relative to that of A. The intensity of the emergent light is :
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a) I0
0%
b) I0/2
0%
c) I0/4
0%
d) I0/8
Explanation
Intensity of light is halved upon passage through first polaroid. Thus intensity of light incident of B I’= I0/2 which is at 45° with A Using Malus’ Law : Answer:(c)
Q.48
Two coherent point sources S1 and S2 are separated by a small distance 'd' as shown. The fringes obtained on the screen will be …[ IIT Mains 2013]
0%
c) semi−circles
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a) points
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b) straight lines
0%
d) concentric circles
Explanation
Wave-front emitted will be spherical thus concentric circles Answer:(d)
Q.49
The graph between angle of deviation δ and angle of incidence I for triangular prism is represented by
0%
a)
0%
b)
0%
c)
0%
d)
Explanation
Answer:(c)
Q.50
In the Young’s double slit experiment using a monochromatic light of wavelength λ, the path difference (in terms of an integer n) corresponding to any point having half the peak intensity is … [ IIT Advance 2013]
0%
a)
0%
b)
0%
c)
0%
d)
Explanation
Possible if Answer:(b)
0 h : 0 m : 1 s
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