AH Exp – Wave Phenomena 04 – Determination of wavelength using Newton’s rings

Aim – To determine the wavelength of sodium light using Newton’s rings

Instructions

▪ Switch on the sodium lamp and observe the interference pattern produced by the lens and glass block.
▪ Move the travelling microscope to position one of the rings in the centre of the cross hairs in the eyepiece view of the travelling microscope.
▪ Let this ring be the ‘n’th ring from the centre. (n=0 for the centre dark spot)
▪ Note the position of the travelling microscope using the Vernier scale.
▪ Move the travelling microscope and measure the diameter of the ring.
▪ Measure the diameter of a number of rings.
▪ Draw a graph of the radius of the ring, r, against the ring number, n. Draw a second graph of the square of the radius of the ring, r, against n.
▪ Use the graph to show the relationship between r and n.
▪ Determine the wavelength, λ, of the light from the graph. Use the relationship r_n²=Rnλ where R, the radius of curvature of the lens is, 1m.

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