Speed of a Wave
Connecting wave speed, frequency, and wavelength
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Speed and Medium for a Wave
School blocks YouTube? | Onsite | | Mythbusters |
Video Instruction showmethephysics.com
F. Speed – the number of meters a single cycle travels per second
1. V = fλ
solve for f:
f = v/λ
inverse relationship
Wave Speed / Doppler Effect
2. Speed of wave depends on the medium
(slower in dense media)
Ex) f = 40. hertz. V = ?
(1) 13 m/s (2) 27 m/s (3) 60. m/s (4)120 m/s Jan 2002 Test
V = fλ
V = 40. Hz(1.5 m)
(3) 60. m/s
Ex) Period = 5.0 sec. V = 20. m/s Wavelength = ?
V = fλ
Need f????
T = 1/f
5.0 sec = 1/f
f = .20 Hz
V = fλ
20. m/s = (.20 Hz)λ
= 1.0 x 102 m
3. Velocity sound = 3.3 x 102 m/s
(Air, Reference Table, room temperature)
School Blocks YouTube? Use link below. Jet breaking speed of sound
School blocks YouTube?
Velocity light in a vacuum
= 3 x 108
m/s
Wikimedia
About how many times faster
is
p. 1 Reference Table
About 1 million times
Gap between time you see lightning and time you hear thunder tells ....
... distance of lightning
If time gap is small?
Lightning is close
Large gap of time?
Lightning far away
Did you know ... Every 5 seconds gap = 1 mile '...you can approximate the storm's distance in miles by counting the seconds between the lightning and thunder and dividing by five. It takes about five seconds for the sonic boom to travel one mile, so if you see the sky illuminated by a streak of lightning and count 10 seconds until you hear the low rumble of the thunder, the storm is about two miles away.'
Vibrating Tuning Fork - Slow Motion
Drdanku YouTube Channel School blocks YouTube?
Wavelength, frequency, Which 3 are determined by the source of a wave?
frequency, period, amplitude.
June 2026
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Check Your Understanding
5 quick questions — pick an answer to see if you’re right.
1. A wave has a frequency of 40. Hz and a wavelength of 1.5 m. What is its speed?
2. A wave has a period of 5.0 s and a speed of 20. m/s. What is its wavelength?
3. Which wave property is determined by the medium rather than by the source?
4. Sound waves travel through the same air. If the frequency doubles, the wavelength
5. You hear thunder 10. s after seeing lightning. About how far away is the strike? (sound speed = 3.3 × 10² m/s)
Measuring the Speed of Sound With an Echo
Students stand 85 m from a large brick wall. One student claps two blocks together, and another uses a phone app to measure the time until the echo returns: 0.50 s.
What is the speed of sound based on these data?
▶ Want a challenge? Open 6 more Regents-style questions (harder · mixed formats)
Challenge score: 0 / 6
C1. The same 680-Hz sound passes from air into water, where sound travels at about 1500 m/s. What happens?
C2. Using the speed of sound found from the echo, substitute numerical values into a mathematical representation that can be used to determine the wavelength of a 680-Hz tone in the same air. Then calculate the wavelength.
C3. On a hot day the students repeat the experiment at the same 85-m distance, and the echo returns in 0.48 s. The wall is to the right of the students. Choose the direction of the velocity of the echo as it returns to the students, and determine its magnitude.
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C4. A student makes the following claim.
Place a check mark in either the Support or Refute box. Justify your response.
C5. Bats use echoes to find insects. A bat hears an echo 0.010 s after its call. About how far away is the insect?
C6. The student timing the echo has a reaction time that could make the measured time off by about 0.05 s. Describe how this uncertainty affects the calculated speed of sound, and describe one change to the procedure that would reduce the effect.