1. A radar pulse traveling at the speed of light is sent to the moon, reflected, and received 2.5 sec after transmission. How far from the moon is the radar transmitter? Ans: 3.75 x 10⁸m
2. A ceiling lamp provides an illumination of 25 lx on a table when it is 0.4 m away. What will the illumination of the table be when the same lamp is 0.2 m away? Ans: 100 lx
3. What is the illumination of a gym floor provided by a 100 cd lamp hanging 5 m above the floor? Ans: 4 lx
4. A public school law requires a minimum illumination of 160 lx on the surface of each student’s desk. Lights are located 2 m above the desks. What is the minimum luminous flux the light bulbs must deliver? Ans: 8042 lm
5. A student wants to compare the luminous flux from a bulb with that of a 1750 lm lamp. The two bulbs illuminate a sheet of paper equally. The 1750 lm lamp is 1.25 m away. The unknown bulb is 1.08 m away. What is its luminous flux? Ans: 1310 lm
6. Two lamps illuminate a screen equally. The first lamp has an intensity of 101 cd and is 5 m from the screen. The second lamp is 3 m from the screen. What is the second lamp’s intensity? Ans: 36.36 cd

1. The second order fringe when 700 nm light falls on a double slit is observed at a 15° angle to the initial beam direction. How far apart are the slits? Ans: 5.41 x 10^-6m
2. Light of frequency 6 x 10¹⁴Hz falls on a pair of slits that are 0.0002 cm apart. The center of the slits is 50 cm from the screen. How far from the central bright line will the first order line appear? Ans: 0.13 m
3. Monochromatic light falling on two slits 0.026 mm apart produces the fourth-order line at a 6.4°angle. What is the wavelength of light used? Ans: 7.25 x 10^-7m
4. Light of wavelength 6.5 x 10^-5cm passes through a single slit and falls on a screen 100 cm away. The third-order dark band is 0.25 cm from the center of the pattern. What is the slit width? Ans: 7.8 x 10^-4m
5. A diffraction grating with 760 lines per cm is used to form a diffraction pattern. The first-order line is 3 cm from the central bright spot. The screen is 80 cm away. What is the wavelength of light used? Ans: 4.93 x 10^-7m
6. At what angle will 710 nm light produce a third order maximum when falling on a grating whose slits are 0.0017 cm apart? Ans: 7.2°

Illumination and Diffraction Notes

Illumination and Diffraction Sample Problems