Question

When the interference occurs with non-coherent sources,________ of the superimposing waves add like_____.

Answer 1

Incoherent sources basically emit light along with frequent as well as random changes of phase among the photons. (Tungsten filament lamps and 'ordinary' fluorescent tubes emit incoherent light).

Complete answer:
When the interference occurs with non-coherent sources, intensities of the superimposing waves add like scalars, $I = {I_1} + {I_2}$. As per the principle of superposition. The resultant displacement of a number of waves in a medium at a specific point is referred to as the vector sum of the individual displacements produced by each of the waves at that specific point.

The phenomena of formation of maximum intensity at some points as well as minimum intensity at some other point when two (or) more waves of equal frequency possessing constant phase difference arrive at a point simultaneously, superimpose with one another is termed as interference.

Types of Superposition of Waves:
As per the phase difference in superimposing waves, interference gets distinguished into two categories given below:
Constructive Interference: When two waves superimpose along with one another in the similar phase, the resultant’s amplitude is equivalent to the sum of the amplitudes of individual waves that results in the light’s maximum intensity , this is termed as constructive interference.

Destructive Interference: When two waves superimpose along with one another in opposite phases, the resultant’s amplitude gets equivalent to the difference in amplitude of individual waves, that results in the light’s minimum intensity, this is termed as destructive interference.

Hence, when the interference occurs with non-coherent sources, intensities of the superimposing waves add like scalars, $I = {I_1} + {I_2}$.

Note: In Physics, interference refers to a phenomenon in which two waves form a resultant wave either of high, low, or possessing the similar amplitude. At any moment or place, an interference can be expected but we can't see everywhere interference patterns because the majority of the sources generate light waves randomly.