TUTORIAL 2 (ALPH20)
1. To demonstrate interference of light waves, Thomas Young allowed light from an illuminated single slit to fall on a pair of narrow closely-spaced slits. Explain:
a. Why light from separate lamp bulbs can never produce an interference pattern?
b. Why double slits used as above do give an interference pattern? How would the interference pattern differ if
i. The double slits had been closer together.
ii. The single slit had been much wider.
2. Atoms emit light in short bursts lasting of the order of nano-seconds. Given the speed of light in air is 3 x 108 ms-1, calculate:
a. The length of a typical wave train of light in air[0.3m]
b. The number of cycles in such a wave train if the wavelength in air is 50nm. [6x10⁶]
3. In a double slit experiment, a screen in positioned at a distance of 0.80m from the two slits. Light of wavelength 590nm is directed at the slits normally to give an interference pattern on the screen with five fringes spaced over a distance of 4.8mm. Calculate the slit spacing. [4.92x10ˉ⁴m]
4. In a double slit experiment, a laser beam is directed normally at a pair of double slits with a slit spacing of 0.50mm. An interference pattern is observed on a screen placed at a distance of 120cm from the slits at right angles to the line from the slits to the screen. Bright fringes are observed on the screen at a spacing of 1.5mm.
a. Calculate the wavelength of the laser light. [625nm]
b. How far and in which direction would the screen need to be moved to change the fringe spacing to 2.0mm? [400mm away]
c. Calculate the fringe spacing if the laser is replaced by monochromatic light source of wavelength 460nm and the screen is placed 800mm...