A Level Physics Practice Exam

What color appears at the center of the diffraction pattern when white light is used?

1. Blue

2. Red

3. Green

4. White

The correct answer is: White

When white light is passed through a diffraction grating or any similar optical setup, it disperses into its constituent colors due to the different wavelengths of light. Each color bends at a slightly different angle; shorter wavelengths (like blue and violet) bend more than longer wavelengths (like red). At the center of the diffraction pattern, the light does not undergo any angular separation and thus remains unchanged. The central maximum, or the brightest point, will correspond to the direct transmission of light without any dispersion—this point effectively remains white because it is composed of all the colors of light blending together. Hence, white light at the center stays as white, which is the combination of all visible wavelengths. The other colors manifest in the surrounding maxima as they get dispersed, but the central point is where no dispersion occurs, reinforcing that the central color is white.