Question

In a Young’s double slit experiment, 12 fringes are observed to be formed in a certain segment of the screen when light of wave length 600 nm is used. If the wavelength of light is changed to 400 nm, the number of fringes observed in the same segment of the screen is given by

• A. 12
• B. 18
• C. 24
• D. 30

Answer 1

The correct option is B

18

$Ym=\frac{m\lambda D}{d}$

$m_1{\lambda }_1=m_2{\lambda }_2$

$m_2=\frac{m_1{\lambda }_1}{{\lambda }_2}=\frac{12\times 600}{400}=18$