DIFFRACTION
1

**Where necessary take the velocity of light as = 3x10**

^{8}ms^{-1}and the velocity of sound as 330ms^{-1}**1. Red monochromatic light falls on a narrow slit. Describe what happens to the diffraction pattern as the slit is slowly opened.**

**2. How would the diffraction pattern in number one be affected if blue light were used instead of red?**

**3. Which would be easier to receive in hilly areas and why, television or radio?**

**4. Why is the diffraction of light much more difficult to observe than the diffraction of microwaves?**

**5. A diffraction grating has 300 lines per mm.**

**Calculate:**

**(a) the angle of diffraction for the first order image for light of wavelength 550 nm**

**(b) the highest order possible with this grating at this wavelength**

**(c) the number of images of the source**

**6. Calculate: (a) the grating spacing for light of wavelength 500 nm passing through a grating where the angle of diffraction for the second order image is 20.5**

^{o}**(b) the number of lines per millimetre on the grating**