You carried out an experiment to measure the wavelength of a monochromatic light source using a diffraction grating - Leaving Cert Physics - Question 2 - 2007

A suitable source of monochromatic light could be a sodium lamp or a laser.

The measurements taken during the experiment include:

1. The distance from the diffraction grating to the screen (D).
2. The distance between the first-order (n=1) and the second-order (n=2) diffraction fringes (x).
3. Adjustments made using the spectrometer for accurate alignment.

The distance (d) between each line on the diffraction grating can be calculated using the formula: $d = \frac{1}{\text{number of lines per meter}} = \frac{1}{600000} = 1.66666 \times 10^{-6} \text{ m}$.

The wavelength ($\lambda$) of the light can be determined using the diffraction formula: $d \sin(\theta) = n \lambda$ Where:

• $\lambda$ is the wavelength.
• $d$ is the distance between the lines on the grating.
• $\theta$ is the angle of diffraction.
• $n$ is the order of the fringe observed. Rearranging this, the wavelength can be found as: $\lambda = \frac{d \cdot \sin(\theta)}{n}$.

One precaution to ensure accurate results is to ensure proper calibration of the spectrometer. Additionally, eliminating external light can help reduce interference in the measurements, such as by conducting the experiment in a dark room.