# The Diffraction Grating - Fringe Brightness and Spacing

1. Dec 14, 2009

### ap_cycles

1. Go to http://www.matter.org.uk/schools/Content/Interference/gratingExplored.html [Broken].
Q1. What is the effect of varying the Wavelength of the light?

The attempt at a solution. The smaller the wavelength, the lesser the degree of diffraction, as evidenced by the narrower intensity envelope, and vice versa. In addition, the spacing between bright fringes is increased when wavelength becomes bigger

Lingering doubt: When the wavelength changes, is the entire spread of diffraction pattern bigger or smaller? When fringe spacing increases, is it always equal to an increase in overall diffraction pattern spread?

Q2. Set the Wavelength to “600 nm” and the Number of slits to “1” for single-slit diffraction. What is the effect of varying the Slit width?

The attempt at a solution. The bigger the slit width, the smaller the degree of diffractionobserved.The entire diffraction pattern spreads wider when the slit width is smaller.

Lingering doubt: Is it right to say that the fringe spacing increases in addition to the widening of the diffraction pattern when the slit width is smaller?

Q3. Set the Number of slits to “2” for double-slit interference. What is the intensity (brightness of the fringes) envelope dependent on? Fyi, the wavelength remains at 600nm

Attempt at solution.It depends on the slit width only.

Lingering doubt:Does changing the screen distance count? Seems that screen distance changes only the magnification of view. Does, imo NO

Q4. What is the spacing of the fringes dependent on?

Attempt at solution. 3 factors: Screen distance, wavelength of light, slit separation.

Lingering doubt Does changes in fringe spacing in any way determine the diffraction pattern spread? * I know this is a repeated question, but this question has been bugging and confusing me!*

Last edited by a moderator: May 4, 2017