Question

A monochromatic beam of light falls on YDSE apparatus at some angle (say $\theta$ ) as shown in the figure. A thin sheet of glass is inserted in front of the lower slit $S_2.$ The central bright fringe (path difference $=0$) will be obtained is-

• A. $\text{At O}$
• B. $\text{Above O}$
• C. $\text{Below O}$
• D. $\text{Anywhere depending on angle}\theta ,\text{thickness of plate}t,\text{and refractive index of glass}\mu$

Answer 1

The correct option is D $\text{Anywhere depending on angle}\theta ,\text{thickness of plate}t,\text{and refractive index of glass}\mu$

$\text{If d sin}\theta =(\mu -1)t,\text{central fringe is obtained at O}$

$\text{If d sin}\theta >(\mu -1)t,\text{central fringe is obtained above O}$

$\text{If d sin}\theta <(\mu -1)t,\text{central fringe is obtained below O}$

<!--td {border: 1px solid #ccc;}br {mso-data-placement:same-cell;}--> Hence, $\left(D\right)$ is the correct answer.