Optical Sensors

Work the problems below. Show all work. Submit your work in a word processing document .

1. A source of green light has a frequency of 6.2 x 10¹⁴ Hz. What is the wavelength in nanometers (nm) and in Å?
2. A flashlight beam has an exit power of 100mW, an exit diameter of 3.8cm, and a divergence of 1.1. Calculate the intensity in mW/cm2 at 55m and the size of the beam at that distance.
3. Suppose a 680-nm beam with a power of 0.2 mW and a 4.5-cm diameter strikes a detector with a 0.2-cm diameter. How many photons strike the detector per second?
4. A photomultiplier has a current gain of 3 x 10⁶. A weak light beam produces 55 electrons/s at the photocathode. What anode-to-ground resistance must be used to get a 2.8 μV voltage from the light pulse? The charge of an electron is 1.6 x 10^-19 coulomb.