Young’s Double Slit Experiment (JEE LEVEL)

(a)    straight                                 

(b)    circular

(c)     equally spaced                  

(d)    having fringe spacing which increases as we go outwards

Ans (d) 

12.

In Young’s experiment, let P and Q be the two slits. A thin film of thickness t and refractive index n is placed in front of P. If \displaystyle \beta be the fringe width and \displaystyle \lambda be the wavelength of light then the central maxima will shift

(a)   towards \displaystyle P\,\,\,by\,\,\,t(n1)\frac{\beta }{\lambda }  

(b)    towards \displaystyle Q\,\,by\,\,t(n1)\frac{\beta }{\lambda }

(c)    towards \displaystyle P\,\,by\,\,nt\frac{\beta }{\lambda }              

(d)    towards \displaystyle Q\,\,by\,\,nt\frac{\beta }{\lambda }

Ans (a) 

13.

Light of wavelength \displaystyle {{\lambda }_{0}}in air enters a medium of refractive index n. If two points A and B in this medium lie along the path of this light at a distance x, then phase difference \displaystyle {{\varnothing }_{0}} between these two points is

(a)    \displaystyle {{\phi }_{0}}\,=\,\frac{1}{n}\,\left( {\frac{{2\pi }}{{{{\lambda }_{0}}}}} \right)\,x  

(b)    \displaystyle {{\phi }_{0}}\,=\,n\,\left( {\frac{{2\pi }}{{{{\lambda }_{0}}}}} \right)\,x               

(c)     \displaystyle {{\phi }_{0}}\,=\,(n1)\,\left( {\frac{{2\pi }}{{{{\lambda }_{0}}}}} \right)\,x         

(d)    \displaystyle {{\phi }_{0}}\,=\,\frac{1}{{(n1)}}\,\left( {\frac{{2\pi }}{{{{\lambda }_{0}}}}} \right)\,x

Ans (b) 

14.

In Young’s double slit experiment, the slits are 2 mm apart and are illuminated with a mixture of two wavelengths \displaystyle {{\lambda }_{o}}\,=\,750\,nm\,\,\,and\,\,\lambda \,=\,900\,nm. The minimum distance from the common central bright fringe on a screen 2 m from the slits where a bright fringe from one interference pattern coincides with a bright fringe from the other is

(a)  1.5 mm                       

(b)   3 mm                               

(c)   4.5 mm                            

(d)   6 mm

Ans (c) 

15.

In the ideal double slit experiment, when a glass plate (refractive index 1.5) of thickness t is introduced in the path of one of the interfering beams (wavelength \displaystyle \lambda ) the intensity at the position where the central maximum occurred previously remains unchanged. The minimum thickness of the glass plate is

 (a)  2 \displaystyle \lambda                      

(b)    \displaystyle \frac{{2\lambda }}{3}       

(c)     \displaystyle \frac{\lambda }{3}    

(d)    \displaystyle \lambda

Ans (a) 

16.

Two wavelengths of light \displaystyle {{\lambda }_{1}} and \displaystyle {{\lambda }_{2}} are sent through a Young’s double slit apparatus simultaneously. If the third order l₁ bright fringe coincides with the fourth order \displaystyle {{\lambda }_{2}}bright fringe then

 (a)   \displaystyle \frac{{{{\lambda }_{1}}}}{{{{\lambda }_{2}}}}\,=\,\frac{4}{3}   

(b)    \displaystyle \frac{{{{\lambda }_{1}}}}{{{{\lambda }_{2}}}}\,=\,\frac{3}{4}   

(c)     \displaystyle \frac{{{{\lambda }_{1}}}}{{{{\lambda }_{2}}}}\,=\,\frac{5}{4}   

(d)    \displaystyle \frac{{{{\lambda }_{1}}}}{{{{\lambda }_{2}}}}\,=\,\frac{4}{5}

Ans (a) 

17.

Two identical sources each of intensity Iohave a separation \displaystyle d\,=\,\frac{\lambda }{8}, where \displaystyle \lambda is the wavelength of the waves  emitted by either source. The phase difference of the sources is \displaystyle \frac{\pi }{4}. The intensity distribution I(q)  in the radiation filed as a function of[ \displaystyle \theta ], which specifies  the direction from the sources to the distant observation point P is given by

 (a)   \displaystyle I\,(\theta )\,=\,{{I}_{o}}\,{{\cos }^{2}}\,\theta              

(b)    \displaystyle I\,(\theta )\,=\,\frac{{{{I}_{o}}}}{4}\,{{\cos }^{2}}\,\left( {\frac{{\pi \theta }}{8}} \right)

(c)     \displaystyle I\,(\theta )\,=\,4{{I}_{o}}{{\cos }^{2}}\,\left( {\frac{\pi }{8}\,(\sin \theta \,+\,1)} \right)                   

(d)    \displaystyle I\,(\theta )\,=\,{{I}_{o}}{{\sin }^{2}}\,\theta

Ans (c) 

18.

In a double slit experiment, instead of taking slits of equal widths, one slit is made twice as wide as the other. Then in the interference pattern

(a) the intensities of both the maxima and the minima increase

(b) the intensity of the maxima increases and minima has zero intensity

(c) the intensity of the maxima decreases and that of minima increases

(d) the intensity of the maxima decreases and the  minima has zero intensity

Ans (a) 

19.

In a Fresnel biprism set-up, l is the distance of the prism from the source slit, A is the angle of the prism and \displaystyle \mu is the refractive index of the material of the prism. Then the separation between the two virtual sources will be equal to 

 (a)  lA ( \displaystyle \mu – 1)/2            

(b) 2lA ( \displaystyle \mu – 1)              

(c)  3lA ( \displaystyle \mu – 1)                

(d) 4lA( \displaystyle \mu – 1)

Ans (c) 

20.

Consider a usual set up of Young’s double slit experiment with slits of equal intensity as shown in the figure. Take ‘O’ as origin and the Y axis as indicated. If average intensity between y₁ = – \displaystyle \frac{{\lambda D}}{{4d}} and y₂ = + \displaystyle \frac{{\lambda D}}{{4d}} equals ‘n’ times the intensity of maxima, then ‘n’ equals