INTERFERENCE OF WAVES

Is the phenomena in which two waves superpose to form a resultant wave of greater or lower amplitude

OR

Is the phenomenon that occurs when two waves meet while travelling along the same medium.

PRINCIPLE OF SUPERPOSITION

The principle of superposition states that:-

²The resultant displacement at any point is equal to the sum of the displacements of different waves at the point’’

TYPES OF INTERFERENCE

There are two categories of interference of waves.

i)        Constructive interference.

ii)       Destructive interference.

CONSTRUCTIVE INTERFERENCE

Is the interference that occurs at any location along the Medium where two interfering waves have displacement.

Crest + Crest =   Crest (large amplitude)

Trough + trough = Trough (large amplitude)

CONDITIONS FOR CONSTRUCTIVE INTERFERENCE

 For constructive interference to occurs

i)        Two waves should be in phase

 i.e. Two crests meet or Two through meet.

ii)      The distance from the observer to each source of waves should be equal.

EFFECTS OF CONSTRUCTIVE INTERFERENCE

i)        Two waves of reinforce each other hence larger amplitude is obtained

ii)       A bright fringe is obtained on the screen for light waves.

       

DESTRUCTIVE INTERFERENCE

Is the interference that occurs at any location along the Medium where the interfering waves have a displacement in the opposite direction.

Crest + Trough = zero wave. 

CONDITIONS FOR DESTRUCTIVE INTERFERENCE

For destructive interference to occur

i)      Two waves should be out of phase

Eg. Crest meets with trough.

ii)    The distance from observed to each source is un equal.

EFFECTS OF DESTRUCTIVE INTERFERENCE

i)        Two waves cancel the effects of each other

ii)       A dark fringe is obtained on the screen for light waves.

CONDITIONS OF INTERFERENCE

i)      The two sources of waves should emit continuous  waves of the same wavelength and same time period (frequency)

Þ Sources should be coherent sources

ii)     The two sources should be very close to each other.

iii)   The waves emitted by two sources should either have zero phase difference or no phase difference.

APPLICATIONS OF INTERFERENCE OF WAVES

i)        Applied when creating histograms.

Histogram – Is a photograph of an interference pattern which is able to produce   a three dimensional image when suitably illuminated.

ii)       Destructive interference is used in noise – reduction system such as earphones.