Measurement of the wavelength of monochromatic light (using the laser)

Apparatus

Laser, diffraction grating (600 lines per mm), 2 metre sticks.

Procedure

• Clamp a metre stick horizontally in a stand.

• Allow the laser beam to hit the metre stick normally (at 90°).

• Move the metre stick sideways until the spot is on the 50 cm mark.

• Place the grating between the laser and the metre stick, at right angles to the beam.

• Observe the interference pattern on the metre stick - a series of bright spots.

• Calculate the mean distance x between the centre (n=1) bright spot and the first (n =1) bright spot on both sides of centre.

• Measure the distance D from the grating to the metre stick.

• Calculate θ using $θ = \frac{x}{D}$

• Calculate the distance d between the slits, using $d = \frac{1}{N}$, where N is the number of lines per metre on the grating.

• Calculate the wavelength λ using $nλ = d \sin θ$.

• Repeat this procedure for different values of n and get the average value for λ.

---

Physics Experiments

Measurement of the wavelength of monochromatic light (using the laser)

Results

n	x/m	D/m	θ/°	λ/m

Average λ =