A) \[1.2\times {{10}^{-7}}m\]
B) \[650\times {{10}^{-9}}m\]
C) \[120\times {{10}^{7}}m\]
D) \[650\times {{10}^{5}}m\]
Correct Answer: A
Solution :
[a] There is air on both sides of the soap film. \[\therefore \] the reflections of the light produce a net \[180{}^\circ \]phase shift. The condition for bright fringes is \[2t=(m+{\scriptstyle{}^{1}/{}_{2}}){{\lambda }_{film}}\] \[t=\frac{(m+{\scriptstyle{}^{1}/{}_{2}}){{\lambda }_{film}}}{2}=\frac{(m+{\scriptstyle{}^{1}/{}_{2}})\lambda }{2n}\] \[=\frac{({\scriptstyle{}^{1}/{}_{2}})(650\times {{10}^{-9}}m)}{2(1.41)}=1.2\times {{10}^{-7}}m\]
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