Increase the distance x, from grating to screen. This reduces percentage error. Find the average value for . Take care measuring distances to avoid parallax error when using the metre stick.
Safety Precaution Take care when using a laser to avoid shining it directly into someone’s eyes.
DEMONSTRATION 14.2
Demonstration of Wave Nature of Light (Laser Method) Apparatus Laser, diffraction grating (or Young’s slits), screen
Procedure Shine laser through grating (or slits) onto screen.
Observation There is interference pattern of bright and dark fringes.
Conclusion As only waves undergo the phenomena of interference, it can be concluded that light is a wave motion.
SAMPLE PROBLEM 14B
The first order image of a monochromatic light source is at an angle 29 to the zero order image. The diffraction grating has 800 lines per millimetre. What is the wavelength of that light? Give your answer in nanometres.
