En anglais

Speed equals frequency times wavelength

Science · Waves, Light & Sound · ages 15-16

Name ______________________ Date ____________

What does frequency count?
- The greatest displacement from rest
- Complete wave cycles passing per second
- The material's flow distance per second
Which is the wave equation?
- Speed equals frequency times wavelength
- Speed equals frequency plus wavelength
- Speed equals wavelength over period squared
Sound can travel across a vacuum.
Circle one: True False
A timer starts at crest zero and stops at the tenth following crest. These ten complete intervals take 5 seconds. Find the frequency in Hz.
Answer: ______________
A 500 Hz sound moves at 340 m/s. What is its wavelength?
- 0.68 m
- 1.47 m
- 170000 m
A wave has frequency 4 Hz. What is its period in seconds?
Answer: ______________
A reflector is 85 m away. The time from a clap to its echo is 0.5 s. Which calculation gives sound speed?
- 85 ÷ 0.5 = 170 m/s
- 170 ÷ 0.5 = 340 m/s
- 170 × 0.5 = 85 m/s
Sound speed stays at 340 m/s while a tone changes from 170 Hz to 340 Hz. What happens to its wavelength?
- It doubles from 2 m to 4 m
- It stays at a wavelength of 2 m
- It halves from 2 m to 1 m

Answer key

For grown-ups. Fold this page away before handing over the rest.

Complete wave cycles passing per second · Frequency is a complete-cycle count divided by elapsed time, expressed in cycles per second or hertz.
Speed equals frequency times wavelength · The wave equation is v = fλ: frequency multiplied by wavelength gives speed.
False · Sound is a mechanical disturbance and needs a material medium. A vacuum provides none.
2 · Ten complete cycles take five seconds, so f = 10 ÷ 5 = 2 Hz.
0.68 m · λ = v ÷ f = 340 ÷ 500 = 0.68 m.
0.25 · T = 1 ÷ f = 1 ÷ 4 = 0.25 s.
170 ÷ 0.5 = 340 m/s · The sound travels 85 m out and 85 m back. Divide the total 170 m by 0.5 s to get 340 m/s.
It halves from 2 m to 1 m · At the stated speed, the wavelengths are 340 ÷ 170 = 2 m and 340 ÷ 340 = 1 m.