Speed equals frequency times wavelength

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

Name ______________________ Date ____________

What does frequency count?
- How tall a wave is
- How many waves pass per second
- How fast a medium flows
What is the wave equation?
- Speed equals frequency times wavelength
- Speed equals frequency plus wavelength
- Speed equals wavelength over period squared
Sound can travel across empty space.
Circle one: True False
Ten ripples pass a straw in 5 seconds. What is the frequency in hertz?
Answer: ______________
A 500 Hz sound moves at 340 m per 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: ______________
Why does timing an echo give the speed of sound?
- Echoes travel faster
- Distance over time for the round trip gives speed
- Echoes only work indoors
In air the speed is fixed. A whistle jumps from 170 Hz to 340 Hz. What happens to its wavelength?
- It doubles
- It stays the same
- It halves to 1 m

Answer key

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

How many waves pass per second · Frequency is measured in hertz, waves per second.
Speed equals frequency times wavelength · Multiply how often waves pass by how long each is.
False · Sound is a longitudinal wave that needs particles to shuffle.
2 · Divide the wave count by the seconds.
0.68 m · Divide speed by frequency: 340 over 500.
0.25 · Period is one over frequency.
Distance over time for the round trip gives speed · Speed is distance divided by time.
It halves to 1 m · Fixed speed means frequency and wavelength trade off.