A student carries out an experiment to investigate the effect of a grating on beams of light from three different lasers - Scottish Highers Physics - Question 10 - 2019

To calculate the wavelength λ, we use the formula:

$d \sin(θ) = m \lambda$

Where:

• d = 3.3 × 10⁻⁶ m (slit separation)
• θ = 8.9° (angle)
• m = 1 (first order maximum)

Rearranging gives:

$λ = \frac{d \sin(θ)}{m}$

Substituting the values:

$λ = \frac{3.3 × 10^{-6} m \times \sin(8.9°)}{1}$

Calculating:

$λ ≈ 5.1 × 10^{-7} m (510 nm)$

The colour of the light from this laser is green, as the calculated wavelength falls within the visible spectrum range for green light.

The suggestion is incorrect because increasing the slit separation to 5.0 × 10⁻⁶ m would lead to larger diffraction angles, making it even more challenging to measure the wavelength accurately. Smaller angles produce a more precise measure, reducing the percentage of uncertainty.