SME
Grade 4 Science · Problem type
Amplitude from crest to trough
Use this for “A wave is 12 cm from crest to trough. What is its amplitude?”
Diagram
Crest to crest is one wavelength, 40 cm.
The crest rises 6 cm above the middle.
Crest to trough: 12 cm
This is an example. Type your own values to start a new problem.
2
×
Amplitude (cm)
=
Crest to trough (cm)
Wavelength
example
Formulas
2 × 6 = 12
2 × amplitude = crest to trough
Assumptions
•
Amplitude is how far the wave rises above the middle line.
•
From the top of a crest to the bottom of a trough is twice the amplitude.
•
A bigger shake makes a taller wave: more energy. A louder sound is a wave with a bigger amplitude.
Step-by-step
WE KNOW
Crest to trough: 12 cm
Wavelength: 40 cm
FIND
amplitude
Step 1 · Find amplitude
2 × ? = 12
2 × amplitude = crest to trough
Half of crest to trough is the rise above the middle.
Amplitude = 12 ÷ 2
Amplitude = 6 cm
Check
Put the numbers back in. Both sides should match.
2 × 6 = 12 ✓
Topic check
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