A certain type of film requires an exposure time of 0.013 s with an f /1.8 lens setting. Another type of film requires twice the light energy to produce the same level of exposure. What f - stop does the second type of film need with the 0.013 s exposure time? (Common f - stops are 1, 1.2, 1.4, 1.8, 2, 4, 8, 11)

Amichelson interferometer operating at a 600 nm wavelength has a 3.02-cm-long glass cell in one arm. to begin, the air is pumped out of the cell and mirror m2 is adjusted to produce a bright spot at the center of the interference pattern. then a valve is opened and air is slowly admitted into the cell. the index of refraction of air at 1.00 atm pressure is 1.00028.how many bright-dark-bright fringe shifts are observed as the cell fills with air?