What is the wavelength of a light ray that has a frequency of 7.4 E12 Hz?

Two point charges are separated by a certain distance. how does the strength of the electric field produced by the first charge, at the position of the second charge, change if the second charge is doubled? a. the field does not change b. the field strength decreases by half. c. the field strength doubles d. the field strength quadruples

The voltage applied across a given parallel-plate capacitor is doubled. how is the energy stored in the capacitor affected?

The built in flash in a compact camera is usally capable of giving correct exsposure for distance up to how many meters?