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This section includes 7 InterviewSolutions, each offering curated multiple-choice questions to sharpen your Current Affairs knowledge and support exam preparation. Choose a topic below to get started.
| 1. |
When an unpolarised light of inensity `I_0` is incident on a polarizing sheet, the intensity of the light which does not get transmittted isA. `I_0`B. ZeroC. `(1)/(4)I_0`D. `(1)/(2)I_0` |
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Answer» Correct Answer - D `50%` of light is not transmitted. |
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| 2. |
What is the shape of the wavefront in each of the following cases ? (a) light diverging from point source. (b) light emerging out of a convex lens when a point source is placed at its focus. ( c) the portion of the wavefront of light from a distant star intercepted by earth.A. Cylindrical wavefrontB. Plane wavefrontC. Converging wavefrontD. Diverging wavefront |
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Answer» Correct Answer - B Plane wavefront. A parallel beam emerges from the lens . |
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| 3. |
When the same monochromatic ray of light travels through glass slab and through water, the number of waves in glass slab of thickness 6 cm is same as in water column of height 7 cm. If refractive index of glass is `1.5`, then refractive index of water isA. `1.258`B. `1.269`C. `1.286`D. `1.310` |
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Answer» Correct Answer - C No. of waves in the glass slab of thickness `t_g` = No. of waves in the water column of height `h_w`. The optical path in a medium of thickness t, and R.I. `mu` is `mu xx t` . Using this we get , `mu_g xx t_g = mu_w xx h_w` `:. ""mu_w=(mu_g xx t_g)/(h_w)=(1.5 xx 6)/(7)=(9)/(7)=1.286` |
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| 4. |
When the same monochromatic ray of light travels through glass slab and through water, the number of waves in glass slab of thickness 6 cm is same as in water column of height 7 cm. If refractive index of glass is `1.5`, then refractive index of water isA. `1.25`B. `1.5`C. `1.33`D. `1.75` |
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Answer» Correct Answer - C Number of waves in a medium (N) `=("Thickness")/("Wavelength in the medium")` `:. N_("glass")=N_("water")` `:. (4)/(lambda_g)=(5)/(lambda_w) :. (lambda_g)/(lambda_w)=(4)/(5)` but `lambda prop (1)/(R.I.) :. (n_w)/(n_g)=(lambda_g)/(lambda_w)` `:. n_W=n_g xx (lambda_g)/(lambda_w)=(5)/(3) xx(4)/(5)=(4)/(3)=1.33` |
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| 5. |
The periodic time of rotation of a certain star is 22 days and its radius is `7 xx 10^(8)` metres . If the wavelength of light emitted by its surface be `4320 Å`, the Doppler shift will be (1 day = 86400 sec )A. 0.33ÅB. 0.33ÅC. 3.3ÅD. 33Å |
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Answer» Correct Answer - A The Doppler shift `Delta lambda ` is given by `(Delta lambda)/(lambda)=(v)/(c) "but" v= r omega=r* (2pi)/(T)` `:. (Delta lamdba)/(lambda)=(2pi r)/(T xx c)` `:. Delta lambda=(2pi r * lambda)/(T xx c)` `=(2 xx 3.14 xx 7 xx 10^(8) xx 4320 xx 10^(-10))/(22 xx 86400 xx 3 xx 10^8)` `=(7 xx 3.14 xx 10^(-10))/( 11 xx 20 xx 3)` `=0.033 xx 10^(-10) m =0.033 Å` |
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| 6. |
The `6000Å` line emitted by a gaseous element in a star iis found to have red shift of ` 15Å`. What is the speed with which the star is receding from the earth ? `(c=3 xx 10^(8) m//s )`A. `5xx10^(5) m//s `B. `6xx10^(5) m//s `C. `7.5xx10^(5) m//s `D. `9xx10^(5) m//s ` |
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Answer» Correct Answer - C The wavelength shift ( Red shift ) `Delta lambda` is given by ` Delta lambda=((v)/(c))lambda ` `:.""v=c((Delta lambda)/(lambda))=3 xx 10^(8) xx (15 xx 10^(-10))/(6000 xx 10^(-10))` `:. ""v=(45xx10^(8))/(6 xx 10^(3))=7.5xx10^(5) m//s ` |
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| 7. |
A light is travelling from air a medium the velocity of light in a medium is reduced to to 0.75 times the velocity n air assume that angle of incidence I is very small the deviation of the ray isA. `delta=i`B. `delta=(i)/2`C. `delta=(i)/4`D. `delta=2r ` |
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Answer» Correct Answer - C `(V_a)/(V_m)=(sin i)/(sin r) :. (V_a)/((3)/(4)V_a)=(i)/(r)=(4)/3` `:. 3i=4r :. r=(3)/4 i ` `delta=i-r :. delta=i-(3)/4 i=(i)/(4)` |
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| 8. |
The wave number of two waves are ` 2.5 xx 10^(6)`/ metre and ` 2 xx 10^(6)`/metre. What is the difference between their wavelengths ?A. `5000Å`B. `4000Å`C. `2000Å`D. `1000Å` |
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Answer» Correct Answer - D Wavelength `=(1)/("Wave number ")` `:. lambda_1=(1)/(2.5 xx 10^(6))=4 xx 10^(-7)` m `and lambda_2=(1)/(2 xx 10^(6))= 5 xx 10^(-7) m` `:. lambda_2- lambda_1=10^(-7)m=10^(-7) xx 10^(10)=10^(3)Å` |
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| 9. |
A strone thrown into still water, creates a circular wave pattern moving radially outwards. If r is the distance measured from the centre of the pattern. The amplitudeof the aves varies asA. `r^(-1//2)`B. `r^(-1) `C. `r^(-2)`D. `r^(-3//2 )` |
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Answer» Correct Answer - B The stone acts like a point source of light and producers spherical waves in 3 dimensions and circular wave in 2 dimensions. The intensity(I) due to a spherical wavefront at a distance r is proportional to `(1)/(r_2)` and the amplitude ` A prop (1)/r ` . In this case , r is the distance of the point from the centre of the pattern. `:. A prop r^(-1)` |
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| 10. |
The difference in speeds of a rya of light in galss and wate is ` 2.5 xx 10^(7) m//s `. If the R.I. of glass and water are `(3)/2 and (4)/3` respectively, then the velocity of light in air isA. a) `2 xx 10^(8) m//s `B. b) `2.25 xx 10^(8) m//s `C. c) `3 xx 10^(8) m//s `D. d) `2.5 xx 10^(8) m//s ` |
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Answer» Correct Answer - C `V_g=(V_(a))/(3//2)=(2)/(3)V_a, V_w=V_w=(V_a)/(4//3)=(3)/(4) V_a ` `:. (3)/(4)V_a -(2)/(3)V_a=(1)/(12)V_a=2.5 xx 10^(7)` `:. V_a=12 xx 2.5 xx 10^(7) =3 xx 10^(8) m//s ` |
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| 11. |
A Light wave travels from a rarer medium to a denser medium. What is its frequency in the denser medium of R.I. 1.5, if its frequency in the rare medium ` 4.5 xx 10^(14)` Hz ?A. `3 xx 10^(14)Hz `B. `6.75 xx 10^(14) Hz `C. `5 xx 10^(14) Hz `D. `4.5 xx 10^(14)Hz ` |
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Answer» Correct Answer - D The frequency does not change with change of medium. |
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| 12. |
A point source of monochromatic light is situated at the centre of a circle. What is the phase difference between the light waves passing through the end points of any diameter ?A. `(pi)/2`B. `pi`C. `(3pi)/2`D. zero |
| Answer» Correct Answer - D | |
| 13. |
The frequency of radio waves corresponding to wavelength of 20 m isA. ` 3 xx 10^(7) Hz `B. `1.5 xx 10^(7)` HzC. `5 xx 10^(-7) Hz `D. `3 xx 10^(6) Hz ` |
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Answer» Correct Answer - B `n=(c)/lambda =(3 xx 10^(8))/(20)=1.5 xx 10^(7) Hz ` |
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| 14. |
A rays of light travel frons A to B , where the geometrical distance AB=8cm in air. It passes through two transparent media havin `n_1=1.5 and n_2=1.75` as shown in the figure . What is the optical path between A and B ? A. 8 cmB. 5 cmC. 10 cmD. 15 cm |
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Answer» Correct Answer - C Optical path `= nxx t ` `:.` Optical path `= 1.5 xx 1+ 1.75 xx 2+5 xx 1=10` cm |
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| 15. |
Two point on a plane wavefront corresponding to ` lambda=5000 Å` are separated by a distance of 2mm. What is the phase difference between those points?A. `(pi)/2 ` radianB. ZeroC. `(2pi)/(lambda)(2 xx 10^(-3))` radianD. `pi` radian |
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Answer» Correct Answer - B All points on a wave front are in the same phase . `:.` The phase difference between any two points is zero . |
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| 16. |
Light enters from air into a medium of R.I. 1.5. What is the percentage change in its wavelength?A. `25%`B. `33.33%`C. `66.66%`D. `11.11%` |
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Answer» Correct Answer - B `lambda_(m)=(lambda_a)/(3//2)=(2)/(3)lambda_a` `:.` change `=lambda_a-(2)/(3) lambda_a=(lambda_a)/(3)` `:.` Percentage change in ` lambda=33.33%` |
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| 17. |
A ray of light of frequency `5 xx 10^(14)` Hz is passed through a liquid . The wavelength of light measured inside the liquid is found to be 450 nm . Calculate (i) wavelength of light in vacuum (ii) refractive index of liquid (iii) velocity of light in the liquid . Take velocity of light in vacuum as ` 3 xx 10^(8) ms^(-1)`A. ` 1.5`B. `1.33`C. `1.25`D. `1.8` |
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Answer» Correct Answer - B `V_L=v lambda= 5 xx 10^(14) xx 450 xx 10^(-9)` `= 225 xx 10^(6) = 2.25 xx 10^(8) m//s ` `:. n=(C)/(V_L)=(3 xx 10^(8))/(2.25 xx 10^(8))=(4)/(3)` |
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| 18. |
The optical path of a monochromatic light is the same if it goes through 2.00 cm of glass or 2.25 cm of water. If the refractive index of water is 1.33, what is the refractive index of glass?A. ` 2. 25 xx 10^(8) m//s `B. `1.5 xx 10^(8) m//s `C. `2 xx 10^(8) m//s `D. `1.75 xx 10^(8) m//s ` |
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Answer» Correct Answer - C Optical path = n ` xx ` distance travelled in the medium `:. ""n_g xx 2 =2.25 xx (4)/3` `:. n_g=2.25 xx (4)/3 xx (1)/2 =1.5` `:. V_g=(C)/(n_g)=(3 xx 10^(8))/(1.5)= 2 xx 10^(8) m//s ` |
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| 19. |
The optical path of a monochromatic light is the same if it travels through 4 cm of glass or 4.5 cm of water . If the refractive index of galss is 1.5, then the refractive index of water isA. 1.2B. 1.33C. 1.42D. 1.46 |
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Answer» Correct Answer - B Optical path `=n_1 d_1=n_2d_2 ` `:. 1.5 xx 4=4.5 xx n_2 " " :. n_2=(6)/(4.5)=1.33 ` |
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| 20. |
A ray of light is incident on a galss slab making on angle of ` 30^(@)` with the surface . If the angle of refraction in glass is ` 33^(@)`, the angle of deviation of the ray during its passage through the galss slab isA. `30^(@)`B. `27^(@)`C. `40^(@)`D. `20^(@)` |
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Answer» Correct Answer - B `r=33^(@), i=60^(@) " " :. delta=60^(@)-33^(@)=27^(@)` |
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| 21. |
Ordinary light incident on a glass slab at the polarising angle suffers a deviation of ` 22^(@)`. In this case, the angle of refraction isA. `56^@`B. `34^(@)`C. `68^(@)`D. `22^@` |
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Answer» Correct Answer - B `delta=i-r=22^(@)` but `i+r=90^(@)` ` :. (i+r)-(i-r)=90^(@)-22^(@)` `:. 2r=68^(@) " " :. r=34^(@)` |
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| 22. |
A beam of light incident on a polaroid and the polaroid is rotated through `360^(@)` , about the direction of the incident beam as the axis. If there is no change in the intesity of the transmitted light then the incident light may beA. Linearly polarisedB. Partially polarisedC. UnpolarisedD. Completely plane polarised |
| Answer» Correct Answer - C | |
| 23. |
Herapathite (iodo sulphate of quinine ) is used in the production ofA. an achromatic prismB. a polaroidC. a biprismD. a solar cell |
| Answer» Correct Answer - B | |
| 24. |
A ray of light passes from vaccume into a medium of refractive index n. if the angle of incidence is twice the angle of refraction, then the angle of incidence isA. `2 sin^(-1)""(n/2)`B. `2 cos^(-1)""(n/2)`C. `cos^(-1)""(n/2)`D. `2sin^(-1)(n)` |
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Answer» Correct Answer - B `n=( sin i)/(sin r)=(sin i)/(sin""((i)/2))=(2 sin""((i)/2)cos""((i)/(2)))/(sin""((i)/(2)))` `=2 cos ""((i)/(2)):. (n)/2= cos ""((i)/2) :. i=2cos^(-1)""((n)/2)` |
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| 25. |
A wave travelling in air falls on a glass plate . It is partly reflected and partly refracted. What is the phase difference between the reflected and refracted waves ?A. `2pi`B. `pi`C. `(pi)/2`D. zero |
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Answer» Correct Answer - B The wave in air, incident on a glass plate is partly reflected and partly refracted. For the ray reflected at a denser medium there is a phase change of `pi`. But for refraction from air to glass, there is no phase change . `:.` There is a phase difference of `pi` between the reflected and refracted waves. |
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| 26. |
A ray of light falls on a transparent glass slab of refractive index 1.53 . If the reflected ray is perpendicular to the refracted ray , then the angle of incidence is approximately equal toA. ` 28^(@)`B. `38^(@)`C. `48^(@)`D. `57^(@)` |
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Answer» Correct Answer - D `n=tan i:. i=tan^(-1)(n)=tan^(-1)(1.53)=57^(@)` |
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| 27. |
A ray of light travelling from air to glass is deviated by an angle of ` 24^(@)`. If the reflected and refracted rays are at right angles then the angles of incidence isA. `48^(@)`B. `57^(@)`C. `28^(@)`D. `24^(@)` |
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Answer» Correct Answer - B `i+r=90^(@) and i-r=24^(@)` `:. 2i=90^(@)+24^(@)=114^(@) " " :. i=57^(@)` |
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| 28. |
The refractive index of glass w.r.t. a medium is `4/3` . If ` V_m-V_g=6.25 xx 10^(7) m//s `, then the velocity of light in the medium will beA. ` 2.5 xx 10^(8) m//s `B. `2.25 xx 10^(8) m//s `C. `1.875 xx10^(8) m//s `D. `1.5xx10^(8) m//s ` |
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Answer» Correct Answer - A `""_(m) n_(g)=(V_(m))/(V_g)=(4)/(3) :. V_m=(4)/(3)V_g` `:. V_m-V_g=V_g((4)/3-1)=(V_g)/(3)` `:. (V_g)/(3)=6.25 xx 10^(7)` `:. V_g=1.875 xx 10^(8) m//s ` `V_m=(4)/(3)V_g=2.5 xx 10^(8) m//s ` |
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| 29. |
If the refractive index of glass is ` sqrt(3)`, then its polarising angle will beA. `30^(@)`B. `45^(@) `C. `60^(@)`D. `90^(@)` |
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Answer» Correct Answer - C `n=sqrt(3)=tani_p " " :. i_p=tan^(-1)(sqrt(3))=60^(@)` |
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| 30. |
If the polarising angle for red light is ` 60^(@)`, for a certain medium, then the polarising angle for the blue light for the same medium will beA. `60^(@)`B. less than ` 60^(@)`C. `45^(@)`D. more than ` 60^@` |
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Answer» Correct Answer - D `tan i_p=n,n_("blue") gt n_("Red")" " :. (i_p)_("blue") gt 60^(@)` |
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| 31. |
The relation between the polarising angle `(i_(p))` and the refractive index (n) of the medium is given byA. `n sin i_(p)=1 `B. `n cot i_(p)=1`C. `n tan i_(p)=1 `D. `n cos i_p=1` |
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Answer» Correct Answer - B `tan i_p=n " ":. (1)/(cot i_p)=n " " :. n cot i_p=1` |
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| 32. |
AN unpolarised beam of light is incident at the polarising angle on the surface of a transparent medium of refractive index 1.6. The angle of refraction in the medium isA. `58^(@)`B. `29^(@)`C. `32^(@)`D. `42^(@)` |
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Answer» Correct Answer - C `tan(i_p)=1.6` `:. i_p=tan^(-1) (1.6)=58^(@) " ":. r=90^(@)-58^(@)=32^(@) ` |
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| 33. |
The wave number of a beam of light in air is ` 2.5 xx 10^(6)` per metre. What is its wavelength in glass of refractive index 1.6 ?A. `2000 Å `B. `2500Å`C. `2750Å`D. `3000Å` |
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Answer» Correct Answer - B `lambda_("air")=(1)/("wave number in air ")` `=(1)/(2.5 xx 10^(6))=4 xx 10^(-7)m =4000 Å` By definition , `""_(a)n_g=(v_("air"))/(v"glass")=(lambda"air")/(lambda_("glass"))` `:. lambda_(g)=(lambda_("air"))/(""_(a)n_g)=(4000)/(1.6)=2500Å` |
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| 34. |
The wavelength of green light in air is 5400 A.U. Its wavelength in the glass of refractive index 3/2 isA. a. 5400ÅB. b. 2700 ÅC. c. 3600 ÅD. d. 8100 Å |
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Answer» Correct Answer - C `n=(V_a)/(V_g)=(n lambda_a)/(n lambda_g)=(lambda_g)/(lambda_g)` `:. lambda_g=(lambda_a)/(n)=(5400)/(3//2)=3600Å` |
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| 35. |
Green light of wavelength 5460Å 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=3 xx 10^(8) ms^(-1))`nA. `3640Å`B. `5460Å`C. `4861Å`D. `6240Å` |
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Answer» Correct Answer - A `n=(v_a)/(v_m)=(lambda_a)/(lambda_m) :. lambda_(m)=(lambda_a)/(n)=(5460)/(1.5)=3640Å` |
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| 36. |
The wavelength of light in vacuum is ` lambda `. The wavelength of light in a medium of refractive index n will beA. `n lambda `B. `(lambda)/(n)`C. `(lambda)/(n^(2))`D. `(n^(2))/(lambda )` |
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Answer» Correct Answer - B `n=(V_a)/(V_m)=(lambda_a)/(lambda_m) :. lambda_(m)=(lambda)/(n)` |
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| 37. |
A ray of light travelling in air is incident at ` 45^(@)` on a medium of refractive index ` sqrt(2)`. The angle of refractive in the medium isA. ` 45^(@)`B. `60^(@)`C. `30^(@)`D. `70^(@)` |
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Answer» Correct Answer - C `n=(sin i)/(sin r)` `:. sin r =(sin i)/(n)=(sin 45^(@))/( sqrt(2))=(1)/(sqrt(2)sqrt(2))=(1)/2` `:. r=30^(@)` |
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| 38. |
A ray of light travelling inside a rectangular glass block `(mu=sqrt2)` is incident on the glass-air surface at an angle of incidence of `45^@`. The refractive index of air is 1. The ray willA. will be absorbed by the glass slabB. will travel in air without any deviationC. will travel parallel to the interface i.e., the angle of refraction will be ` 90^(@)`D. will be reflected back in glass |
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Answer» Correct Answer - C It is incident at the critical angle `n=(1)/(sin C)=sqrt(2)`. |
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| 39. |
Polarised glass is used in sum glasses because:A. it is cheaperB. it is fashionableC. if reduces the intensity of light entering the eyeD. it has good colour |
| Answer» Correct Answer - C | |
| 40. |
The polarisation of an electromagnetic wave is determined byA. only by its magnetic filedB. only by its electric fieldC. by the direction of propagation of the waveD. by both electric and magnetic fields. |
| Answer» Correct Answer - B | |
| 41. |
To which part of the electromagnetic spectrum does a wave of frequency `5xx10^(19)`Hz belong ?A. Ultraviolet regionB. X-ray regionC. Infrared regionD. Visible region |
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Answer» Correct Answer - C `lambda=(C)/(v)=( 3 xx 10^(8))/( 6 xx 10^(12))=5 xx 10^(-5)` `:. lambda = 500 xx 10^(-7) m ` i.e. `lambda gt lambda_R ` `:. ` This lies in the infrared region. |
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| 42. |
If the refractive index of a medium is 1.7, the velocity of light in that medium isA. `1.765 xx 10^(8)` m/sB. `2.5xx10^(8) m//s `C. `1.1 xx 10^(8) m//s `D. `2.2 xx 10^(8) m//s ` |
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Answer» Correct Answer - A `V_m=(V_a)/(n)=(3 xx 10^(8))/(1.7)=1.765 xx 10^(8) m//s ` |
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| 43. |
Light travels through a glass plate of thickness t, having refractive index `mu`. If c is the velocity of light in vaccum, then the time taken by light to travel this thicness of glass isA. `mutc `B. `(mut)/(c)`C. `(t)/(muc)`D. `(tc)/(mu)` |
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Answer» Correct Answer - B `"time"=("distance ")/("velocity") = ( mu t )/(C)` |
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| 44. |
Time taken by sunlight to penetrate 2 mm in a glass slab is of the order of (n=1.5)A. ` 10^(-16)` secB. `10^(-19) ` secC. `10^(-11)` secD. `10^(-7)` sec |
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Answer» Correct Answer - C `V_(g)=( 3 xx 10^(8))/(1.5) = 2xx 10^(8) m//s ` `:. t=("Distance ")/("Velocity")=(2 xx 10^(-3))/(2 xx 10^(8))=10^(-11)` sec |
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