Question

The fringe width for red colour, as compared to that for violet colour is approximately

• A. three times
• B. double
• C. four times
• D. eight times

Answer 1

Answer: (B)

double

For red colour ${\lambda }_r=620-750nm$ and for violet colour ${\lambda }_v=380-450nm$

${\lambda }_r\cong 2{\lambda }_v$

Fringe width $\beta =\frac{\lambda D}{d}\Rightarrow \beta \propto \lambda$

${\beta }_r\cong {2\beta }_v$