Step 1: Set the width of the slit. Keep this value constant throughout the experiment.
Given: Slit width d = 1000 nm = 1 × 10⁻⁶ m

Step 2: Click on "Diffraction Pattern" or "Intensity Profile" option to observe the diffraction pattern as shown in Fig. 3.

Step 3: Change the value of angle of observation (θ) corresponding to the first-order minimum (k = 1).

Step 4: Repeat the process 5 times for different angles of observation. Take the average of the values of λ.

Step 5: Calculate the wavelength (λ) for each observation using the formula:

d  sinθ = kλ    ⇒    λ = d × sinθ / k

Where:

• d — width of the slit
• θ — angle of observation at k^th minimum
• k — order of minima (k = 1 for first-order minimum)
• λ — wavelength to be calculated

Observation Table:

Given: d = 1000 nm = 1 × 10⁻⁶ m,   k = 1

Average Wavelength:

λ_avg = (632.0 + 633.4 + 633.6 + 632.7 + 633.3) / 5
λ_avg = 3165.0 / 5
λ_avg = 633.0 nm

Standard value of He–Ne laser wavelength = 632.8 nm
Percentage Error = |(632.8 − 633.0) / 632.8| × 100 ≈ 0.03%