Interference is the variation of wave amplitude that occurs when waves of the same or different frequency come together.
Regarding waves, destructive interference is very similar to the interference that we think about. Destructive interference means wave pulses are on two opposite sides (one up, one down) while they pass through the same place at the same time. If they have the same amplitude what do you think will happen? Oh, you're very close! They will completely counteract each other. You subtract them. For example, let's say Pulse 1 has an amplitude of 5mm and Pulse 2 also has an amplitude of 5mm. The Resultant Pulse would have an amplitude of 0mm: 5mm-5mm=0mm. When the resultant pulse is equal to 0 it is called complete destructive interference. Not to hard, right?
If they pass each other on two opposite sides, but the amplitudes of the pulses are different, the resultant pulse is still found in the same way- by subtraction! If Pulse 1 has an amplitude of 7mm and Pulse 2 has an amplitude of 3mm, the Resultant Pulse would have an amplitude of 4mm: 7mm-3mm=4mm. The Resultant Pulse will be facing the same direction as the pulse with the bigger amplitude, in this case, Pulse 1.
Fantastic question! That's next: constructive interference. Constructive interference is also when pulses travel through the same point at the same time. However, unlike destructive interference, they are on the same side. In this case, you add the pulses together to get the resultant pulse. Let's take two pulses with amplitudes of 7mm and 3mm again. The Resultant Pulse would be 10mm: 7mm+3mm=10mm.
What does all of this mean? Well, basically when two pulses interfere with one another, a new pulse is created and that is the pulse observed! It can be bigger or smaller. However, immidiately after the pulses pass through each other, they snap back to themselves! The resultant pulse is gone and once again the original pulses are back.
Pretty simple, I know! If you remember to subtract for destructive interference and add for constructive interference, you'll be golden!
Surprisingly enough, this happens in real life, too! Think about the roadtrip you took two summers ago. You were listening to your favorite radio station, 104.3. All of a sudden, it starts to get a bit scratchy. You hear some weird Latin song, and then it goes back to your Pop, then to Latin, then to Pop, then to Latin and then... nothing. Where did the music go? In that time frame when no music was coming from your radio, the Pop station and the Latin American station cancelled each other out. Since they're on the same frequency, the waves coming from each station interfered with the other, leaving with you no music to listen to. Aw man.
