Waves and Sound: Wavelength, Frequency and Speed

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Science · Physics
SP-PHYS-008 · Free to print and use in your classroom · substituteplans.com
Page 2
Waves and Sound: Wavelength, Frequency and
Speed
Science · Physics · Grades 9-11 · 50 minutes
Time needed
50 minutes (one class period)
Prep
Copy the 2-page worksheet (one per student). Write v = f × λ on the board.
Technology
None. A calculator is helpful but not required.
Student
independence
High. Students work alone, then compare answers.
Copies to make
One 2-page worksheet per student
Materials
Pencils, Worksheet, Whiteboard or chalkboard, Calculators (optional)
Goal for today: Students will use v = f × λ and d = v × t to solve wave and sound problems and will classify common
waves as transverse or longitudinal.
Before the bell
☐ Copy the worksheet, one per student (2 pages).
☐ Write on the board: v = f × λ f = 1 ÷ T d = v × t Speed of sound in air (20°C) = 343 m/s
☐ Also write: λ (lambda) = wavelength in meters, f = frequency in hertz (Hz), T = period in seconds.
☐ Keep the answer key on your desk. You do not need to solve anything yourself.
Say this to start
Good morning! Today’s physics work is about waves, including sound. A wave carries energy from place to place. You
will match key words, solve a few problems with a simple formula, and sort different waves into two types. All formulas
and constants are on the board and on the worksheet.
Run of show
Minutes
What you do
What students do
0–5
Take attendance. Hand out the worksheet.
Settle in and take out a pencil.
5–12
Read the board aloud. Example: a wave with frequency 4
Hz and wavelength 3 m has speed 4 × 3 = 12 m/s. Mention
that sound needs matter (air, water or solids) to travel
through.
Follow the example.
12–18
Tell students to do Part A, the matching (questions 1–5).
Match terms to meanings.
18–36
Tell students to do Part B (problems 6–11). Walk the room
and point to the formulas for stuck students.
Solve each problem with units.
36–44
Tell students to do the wave-type table and Part C
(questions 12–14). Then read the answers from the key
aloud.
Classify waves, answer questions and mark
their work.
44–50
Collect all worksheets in one stack.
Hand in the worksheet.

SubstitutePlans.com
Science · Physics
SP-PHYS-008 · Free to print and use in your classroom · substituteplans.com
Page 3
If things go wrong
• If students ask why echo distances are divided by 2, tell them the sound travels to the wall and back, so the
one-way distance is half.
• If students ask about the thunder problem, explain that light arrives almost instantly, so the 3 s delay is just
the sound’s travel time.
• If students confuse frequency and period, write f = 1 ÷ T on the board again and give a quick example: 2 Hz
means the period is 0.5 s.
• If students finish early, use the early finisher list.
Early finishers
• Find the wavelength of a 343 Hz sound wave in air (v = 343 m/s).
• Write two sentences describing the difference between a loud sound and a high-pitched sound.
Support and challenge
• Support: Have students do the matching and problems 6, 7 and 9, and the wave-type table.
• Challenge: A sound has frequency 170 Hz. Find its wavelength in air, then in water where sound travels at
1480 m/s.
Notes for the teacher (you fill this in)
Jot a few lines before you leave. A full Daily Sub Report is in the free Sub Survival Kit at SubstitutePlans.com.
How far the class got / what to pick up next:
Students who were especially helpful:
Anything the teacher should know: