Question

A single slit diffraction pattern is obtained using a beam of red light. If red light is replaced by blue light, then:

• A. The diffraction pattern will disappear.
• B. Fringes will become narrower and crowded together.
• C. Fringes will become broader and will be further apart.
• D. There is no change in the diffraction pattern.

Hint:

In diffraction experiments, the angular width of the fringes is inversely proportional to the wavelength. A shorter wavelength results in narrower fringes.

Answer 1

The Correct Option is B

Step 1: Understanding the Diffraction Pattern In a single slit diffraction experiment, the diffraction pattern is formed when light passes through a narrow slit and spreads out. The angular width of the central maximum is given by the formula: \[ \theta = \frac{\lambda}{a} \] Where: - \( \lambda \) is the wavelength of the light, - \( a \) is the width of the slit, - \( \theta \) is the angle subtended by the central maximum. Step 2: Effect of Changing the Wavelength - The diffraction pattern depends on the wavelength \( \lambda \) of the light used. A longer wavelength results in a wider central maximum (larger angle \( \theta \)), and a shorter wavelength results in a narrower central maximum (smaller angle \( \theta \)). - Red light has a longer wavelength than blue light, so when red light is replaced by blue light, the wavelength \( \lambda \) decreases. - As a result, the angular width of the central maximum will decrease, and the fringes will become narrower and more closely spaced. Step 3: Conclusion The correct conclusion is that the fringes will become narrower and crowded together when red light is replaced by blue light. Thus, the correct answer is: \[ \boxed{(B)} \, \text{Fringes will become narrower and crowded together.} \]