What is frequency ?

What is the frequency of radiation of wavelenth 600 nm ?

What is the frequency of the A.C. supplied in your house?

A siren emitting a sound of frequency 1000 Hz moves away from you towards a cliff at a speed of 10 m/s. (a) What is the frequency of the sound you hear coming directly from the siren ? (b) What is the frequency of the sound you hear reflected off the cliff (c) What beat frequency would you hear ? Take the speed of sound in air as, 330 m/s.

A charged particle oscillates about its mean equilibrium position with a frequency of 10^(9) Hz. What is the frequency of the electromagnetic waves produced by the oscillator?