Waves that add and cancel
Grade 8 Science Worksheet
Circle the best answer, or write your answer on the line.
Each wave repeats every 4 s. Two waves pass the same spot. What is the amplitude of the combined wave there, Ari?
Each wave repeats every 8 s. Two waves rock Esme's boat at the same time. What is the amplitude of the combined wave at the boat?
Jun graphs two ripples at one spot in a pond. What kind of interference do they make there?
- Destructive: B is at a trough whenever A is at a crest, so the water stays flat there
- Constructive: both ripples repeat with a 4 s period, so they must be in step and add up
- Partial: the crests are 2 s apart, a small shift next to the 8 s the graph spans
- Constructive: the ripples have the same size and the same period, so they build a taller ripple
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Two waves at one spot (example data)
wave crest times at the spot (s) A 1, 5, 9 B 1, 5, 9 Each wave repeats every 4 s.
Two waves cross at one spot, and the table lists their crest times there. What kind of interference is it, Kira?
- Destructive: waves with matching crest times are the same wave, so one removes the other
- Neither: waves arriving at a spot at the same moment cannot combine with each other
- Destructive: two crests arriving at the same moment push on each other, so they cancel
- Constructive: the crests arrive together, so the combined wave is taller
Two waves cross at one spot, and the table lists their crest times there. What happens, Luz?
- Fully destructive: crests that arrive at different times meet troughs and cancel each other out
- Fully constructive: B's crests come just 1 s after A's, which is close enough to count as in step
- Partly: B's crests come 1 s after A's in a 4 s period, so the waves are not fully in or out of step
- Fully constructive: both waves repeat with a 4 s period, so their crests must arrive together at the spot
Seat and two speakers (example data)
first speaker (m) second speaker (m) wavelength of the note (m) 5.0 6.5 0.5 Room echoes are ignored.
Two speakers play one note in step. By how many wavelengths do Milo's distances to the speakers differ?
Two speakers play one note in step. By how many wavelengths do the distances from Noah's seat to the speakers differ?
Two speakers play one high note in step. By how many wavelengths do Pia's distances to the speakers differ?
Seats and two speakers (example data)
seat distance to speaker 1 (m) distance to speaker 2 (m) A 4.0 5.0 B 4.0 4.25 C 5.0 5.5 The note has a wavelength of 0.5 m. Room echoes are ignored.
Two speakers play one note in step. Which seat is quiet, Ren?
- No seat: two speakers playing in step add up everywhere, so the room stays loud
- Seat C, where the paths differ by 0.5 m, a whole wavelength, so the waves cancel
- Seat A, where the paths differ by 1.0 m, the biggest gap of the three, so the waves cancel there
- Seat B, where the paths differ by 0.25 m, half a wavelength, so crests meet troughs
Two speakers play one note in step. At which seat is the sound loudest, Tala?
- Seat C, where the paths differ least, 0.25 m, so the two waves arrive nearly together
- Seat A, where the paths differ by 0.75 m, 1.5 wavelengths, so the waves add
- Seat C, since the waves from the nearer speaker are louder than those from the farther one
- Seat B, where the paths differ by 1.0 m, which is 2 whole wavelengths