JEE Main & Advanced Physics Wave Optics / तरंग प्रकाशिकी Question Bank Self Evaluation Test - Wave Optics

  • question_answer
    In a double slit experiment slits \[{{S}_{1}}\], \[{{S}_{2}}\] is illuminated by a coherent light of wavelength\[\lambda \]. The slits are separated by a distance d. The experimental set up is modified by using plane mirrors as shown in figure. Find the fringe width of interference pattern on the screen.              

    A) \[\frac{(3{{D}_{1}}+2{{D}_{2}})\lambda }{d}\]

    B) \[\frac{(2{{D}_{1}}+3{{D}_{2}})\lambda }{d}\]

    C) \[\frac{(3{{D}_{2}}-3{{D}_{1}})\lambda }{d}\]

    D) \[\frac{(3{{D}_{1}}-2{{D}_{2}})\lambda }{2d}\]

    Correct Answer: A

    Solution :

    [a] The fringe width P is given by, \[\beta =\frac{D\lambda }{d}\] where \[D={{D}_{1}}+({{D}_{1}}+{{D}_{2}})+({{D}_{1}}+{{D}_{2}})=3{{D}_{1}}+2{{D}_{2}}\] \[\therefore \,\,\,\beta =\frac{(3{{D}_{1}}+2{{D}_{2}})\lambda }{d}\]


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