A Level Physics Practice Exam

What characteristic distinguishes the light at position A from that at position B when white light emerges from a spectrometer?

1. The light at A will appear white

2. The light at B will appear monochromatic

3. The light at A has higher intensity

4. The light at B will appear completely dark

The correct answer is: The light at A will appear white

In the context of a spectrometer, when white light passes through a prism or a diffraction grating, it disperses into its constituent colors. Position A typically refers to a point where the light has not yet been dispersed significantly, meaning it retains the characteristics of white light, which is a mixture of all visible wavelengths. This retained mixture appears white to the observer. On the other hand, position B is likely to display a specific color or range of colors that have been separated from the original white light. As a result, light seen at position B would be monochromatic or consist of a single wavelength or range of wavelengths. Each color corresponds to a specific wavelength, and thus, that light would not maintain the mixed quality characterizing white light. This understanding explains why the first statement about the light appearing white at position A is correct, as it reflects the undispersed nature of the light before entering the area where separation occurs. The context of the other answers—like higher intensity and darkness—does not apply here, as the intensity can vary based on several factors independent of color separation, and the condition of being completely dark would imply no light is reaching that point, which is not relevant in this scenario focused on light characteristics.