Let’s solve each problem step by step.
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Problem 7:
We have two waves moving toward each other:
- One is a
crest (upward bump) with height = +2 units (from center line to top).
- The other is a
trough (downward dip) with depth = -1 unit (from center line to bottom).
When they meet, we add their heights at every point. Since one is up and one is down, they will partially cancel — this is
destructive interference.
But it’s not *complete* destructive because the sizes are different (+2 and -1). Complete destructive only happens if they’re equal in size but opposite (like +2 and -2).
So when they overlap:
→ Resulting amplitude = 2 + (-1) =
+1 unit
That means the wave after interference will be a small crest of height 1.
✔ Type:
Destructive interference
✔ Why? Because one wave is upward and the other is downward — they oppose each other.
✔ Resulting amplitude height:
1 unit
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Problem 8:
Two waves moving toward each other:
- Left wave: crest, height = +3 units
- Right wave: crest, height = +1 unit
Both are going UP → so when they meet, they add together.
This is
constructive interference — both pushing in same direction.
Resulting amplitude = 3 + 1 =
+4 units
✔ Type:
Constructive interference
✔ Why? Both waves are crests — they reinforce each other.
✔ Resulting amplitude height:
4 units
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Problem 9:
The diagram is blurry, but from what we can see:
There’s a large downward triangle (trough) on left, and a smaller upward triangle (crest) on right.
Assuming:
- Trough depth = -3 units
- Crest height = +1 unit
They are moving toward each other → one down, one up →
destructive interference
Not complete, because sizes don’t match.
Resulting amplitude = -3 + 1 =
-2 units → meaning a trough of depth 2.
✔ Type:
Destructive interference
✔ Why? Opposite directions — one pulls down, one pushes up.
✔ Resulting amplitude height:
2 units deep (or -2, depending on how you measure)
*(Note: If your teacher measures “height” as absolute value, say “2 units”. If signed, say “-2 units”. But since question says “height”, probably mean magnitude → 2 units)*
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Final Answer:
7. Destructive interference — waves are opposite (crest and trough), so they partially cancel. Resulting amplitude height: 1 unit.
8. Constructive interference — both are crests, so they add up. Resulting amplitude height: 4 units.
9. Destructive interference — one is a large trough, one is a small crest; they oppose. Resulting amplitude height: 2 units.
Parent Tip: Review the logic above to help your child master the concept of wave interference worksheet.
