When waves are reflected, absorbed or passed through
Grade 8 Science Worksheet
Circle the best answer, or write your answer on the line.
Ari claps in front of a cliff and hears the echo 0.5 s later. Sound travels about 340 m/s in this air. How far away is the cliff?
Bo's shout echoes back from a far wall after 0.8 s. Sound travels about 340 m/s in this air. How far away is the wall?
Esme rides toward a long tunnel wall and hears a horn echo after 1.2 s. Sound travels about 340 m/s in this air. How far is the wall?
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Window films tested (example data)
film visible light passed (%) ultraviolet passed (%) A 70 90 B 70 2 C 15 1 Jun wants a window film that keeps the room bright but blocks most ultraviolet light. Which film is best?
- Film B, since it passes 70% of the visible light but just 2% of the ultraviolet
- Film C, since a darker film protects the eyes better than a clearer film
- Film A, since it passes the most visible light and the most ultraviolet light, 90%
- Film C, since it passes the least ultraviolet light, 1%, and that settles the choice
Wall layers tested (example data)
layer reflected (%) absorbed (%) transmitted (%) Concrete 90 5 5 Foam 10 85 5 Thin curtain 20 30 50 Kira wants a wall layer that keeps music inside a practice room and also cuts echoes. Which layer should be used?
- Concrete and the thin curtain together, since two layers beat one layer of foam
- Foam, since it passes just 5% of the sound out and reflects just 10% back inside
- Concrete, since it passes just 5% of the sound out, which keeps the music in the room
- Thin curtain, since 50% transmitted is the largest share, so it must do the most work
Speed of light in materials (reference data, rounded)
material speed of light (thousand km/s) Air 300 Water 225 Glass 200 Diamond 124 A ray of light goes from air into glass at an angle. What happens to its speed and path, Milo?
- It slows from 300 to 200 thousand km/s and bends toward the normal
- It slows from 300 to 200 thousand km/s and bends away from the normal
- It slows from 300 to 200 thousand km/s and goes straight on, since both are clear
- It stays at 300 thousand km/s and bends because glass is transparent
A ray of light goes from glass into water at an angle. What happens to its speed and path, Noah?
- It speeds up from 200 to 225 thousand km/s and bends toward the normal
- It slows down to 225 thousand km/s and bends toward the normal
- It keeps its speed of 200 thousand km/s and bends because the two materials differ
- It speeds up from 200 to 225 thousand km/s and bends away from the normal
A ray of light goes from air straight into diamond, along the normal. What happens to it, Pia?
- It speeds up to 124 thousand km/s and goes straight on, since diamond is thicker
- It slows from 300 to 124 thousand km/s but keeps going straight, with no bend
- It keeps its speed and goes straight on, since the angle to the normal is 0°
- It slows from 300 to 124 thousand km/s and bends toward the normal
Sound level behind each sample, three trials (example data)
trial foam (dB) plywood (dB) cork (dB) 1 52 49 63 2 54 61 66 3 50 64 64 Tala tests which sample lets the least sound through. Which conclusion do the data support?
- Foam and plywood tie, since each gave a reading below 55 dB at least once
- Foam, since its readings average 52 dB, the lowest average of the three materials
- Cork, since a higher reading means that more of the sound was blocked
- Plywood, since its first reading, 49 dB, is the lowest of the nine readings in the table
Zee wants a fair test of how foam thickness changes the sound that gets through. Which setup is best?
- Use 2, 4 and 6 cm of the same foam, but turn the speaker up for each thicker sample so the meter can read it
- Use 2 cm of foam, 4 cm of plywood and 6 cm of cork, so each thicker sample is also a new material to test
- Use 2, 4 and 6 cm of the same foam with one speaker, distance and meter, and take one reading of each
- Use 2, 4 and 6 cm of the same foam with one speaker, distance and meter, and take three readings of each
