Assume that 20% of the surface of a membrane filter used to collect particulate matter consists of circular openings with a uniform diameter of 0.45 µm. How many openings are on the surface of a...

Assume that 20% of the surface of a membrane filter used to collect particulate matter consists of circular openings with a uniform diameter of 0.45 µm. How many openings are on the surface of a filter with a diameter of 5.0 cm? What device is employed to make a nondispersive infrared analyzer selective for the compound being determined?