How Speed-Detectors Work? #shorts

How does a catalyst work?

At an airport, a perosn is made to walk through the door wy of a metal detector, for security reasons. If she//he is carrying anything made of metal, the metal detector emits a sound. On what principle does this detector work ?

Statement-1: Doppler formula is not applicable, when detector is moving away from source with speed greater than that of sound. Statement-2: There is always a decrease in pitch of sound if detector moves towards source.

A radiation detector records 9500 counts in 1.00 min. Assuming that the detector records all decays, what is the activity of the radiation source in (a) becquerels and (b) curies?

How does vaccination work