A rotary encoder is connected directly to the spindle of a machine tool to measure its rotational speed. The encoder generates 144 pulses for each revolution of the spindle. In one reading, the encoder generated 267 pulses in a period of 0.25 sec. What was the rotational speed of the spindle in (a) rev/min

Ascientist notices that an oil slick floating on water when viewed from above has many different colors reflecting off the surface, making it look rainbow-like (an effect known as iridescence). she aims a spectrometer at a particular spot and measures the wavelength to be 750 nm (in air). the index of refraction of water is 1.3