A diffraction grating has a slit density of 980. lines/cm. These are illuminated by green light (525 nm). A screen is located 0.950 m from the diffraction grating. At what diffraction angle (in degrees) will you see the 2nd dark fringe

The stopwatch used by a student to measure velocity of a pulse in a slinky was of least count 0.1 second. he stops the stopwatch when a pulse has made 3 journeys from one end to the other of the slinky. he finds the seconds hand to be at 52nd division. calculate the correct time noted by him.