Newton's rings is an experimental setup used to determine the wavelength of light. Here's how you can determine the wavelength of white light using Newton's rings:
Set up the experimental apparatus: Place a plano-convex lens on a glass plate with a convex surface facing upwards. Ensure that the lens is in contact with the glass plate.
Illuminate the setup: Shine a source of white light (such as a lamp or a laser) onto the glass plate and lens.
Observe the interference pattern: Look through the convex surface of the lens. You should see a series of concentric bright and dark rings surrounding the point of contact between the lens and the glass plate. These rings are known as Newton's rings.
Measure the diameter of the rings: Using a magnifying eyepiece or a microscope, measure the diameters of several bright or dark rings.
Determine the radius of curvature: Calculate the radius of curvature (R) of the lens. This can be done using the lens formula or by using a separate calibration procedure.
Calculate the wavelength: Using the formula for the radius (r) of the nth dark or bright ring (Newton's rings formula), which is given by:
r^2 = R * λ * n
where λ is the wavelength of light and n is the order of the ring (starting from the central bright spot as n = 0, n = 1 for the first dark ring, n = 2 for the second dark ring, and so on).
Repeat and average: Repeat the measurements and calculations for multiple rings, and take an average of the calculated wavelengths.
Determine the average wavelength: Once you have the average wavelength, you can determine the wavelength of the white light used in the experiment.
It's important to note that Newton's rings experiment works best when using monochromatic light (light of a single wavelength). However, by using white light, the average wavelength can be determined by considering the interference patterns formed by different colors within the white light spectrum.