Question

Which combination of wavelength and slit width gives the widest central bright spot for single-slit diffraction?

• A. Wavelength- slit width, $600nm-600nm$
• B. Wavelength- slit width, $600nm-300nm$
• C. Wavelength- slit width, $500nm-300nm$
• D. Wavelength- slit width, $400nm-800nm$
• E. Wavelength- slit width, $400nm-400nm$

Answer 1

Answer: (B)

Wavelength- slit width, $600nm-300nm$

Using $bsin\theta =n\lambda$ $⟹\theta \propto \frac{\lambda }{b}=k\frac{\lambda }{b}$ where $k=$ constant

(A) : ${\theta }_A=k\times \frac{600}{600}=k$

Similarly, ${\theta }_B=2k$, ${\theta }_C=1.67k$, ${\theta }_D=0.5k$, ${\theta }_E=k$

Thus data given in option B will make the widest central bright spot.