The equation for missing order in the double-slit diffraction pattern→
The nature of the diffraction pattern due to the double slits depends upon the relative values of $e$ and $d$. If, however, $e$ is kept constant and $d$ is varied, then certain orders of interference maxima will be missing.
We know that, the direction of interference maxima
$(e+d)\:sin\theta=\pm n\lambda \qquad(1)$
The direction of diffraction minima
$e \: sin\theta=\pm m\lambda \qquad(2)$
Divide the equation $(1)$ by equation $(2)$
$\frac{(e+d)}{e}=\frac{n}{m}$
Case (I)→
If $e=d$ then
n=2m
So for $m=1,2,3,....$
The $n=2,4,6,....$
Thus, the $2_{nd}, 4^{th}, 6^{th}, ...$ order interference maxima will be missing.
Case (II) →
If $e=\frac{d}{2}$ then
n=3m
So for $m=1,2,3,....$
The $n=3,6,9,....$
Thus, the $3_{rd}, 6^{th}, 9^{th}, ...$ order interference maxima will be missing.
Angle of Acceptance → If incident angle of light on the core for which the incident angle on the core-cladding interface equals the critical angle then incident angle of light on the core is called the "Angle of Acceptance. Transmission of light when the incident angle is equal to the acceptance angle If the incident angle is greater than the acceptance angle i.e. $\theta_{i}>\theta_{0}$ then the angle of incidence on the core-cladding interface will be less than the critical angle due to which part of the incident light is transmitted into cladding as shown in the figure below Transmission of light when the incident angle is greater than the acceptance angle If the incident angle is less than the acceptance angle i.e. $\theta_{i}<\theta_{0}$ then the angle of incidence on the core-cladding interface will be greater than the critical angle for which total internal reflection takes place inside the core. As shown in the figure below Transmission of lig
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