Astanding wave is produced when two waves traveling in opposite directions meet. the two waves must have equal wavelength and
.

Explanation:

Standing waves are also called stationary waves, which is basically the combination of two waves moving in opposite directions.

However, not all waves that travel in opposite directions form standing waves.

If those waves have the same amplitude, frequency and wavelength, then they will form stationary or standing waves. It's like adding 2 + (-2), which is zero.

Therefore, the missing word here is amplitude.

A standing wave is produced when two waves traveling in opposite directions meet. The two waves must have equal wavelength and  amplitude.

a, c, d, e are all applying about success strategies.

photocells convert light energy to electricity