Question

students made this drawing of a water ripple as seen from the side of a glass container.
diagram: wave moving right, water with waves
what does the drawing show about the energy of the wave as it moves?
a. the energy of the wave increases as shown by the increasing frequency.
b. the energy of the wave decreases as shown by the decreasing amplitude.
c. the energy of the wave remains the same as shown by the same wavelength.
d. the energy of the wave regularly increases and decreases as shown by the peaks and troughs.

Explanation:

1. Recall the relationship between wave energy and amplitude: Wave energy is proportional to the square of the amplitude ($E \propto A^2$).
2. Analyze the diagram: The wave's amplitude (height from rest position to peak) decreases as it moves right.
3. Evaluate options:

• Option A: Frequency (number of waves per unit time) doesn’t increase here; energy isn’t shown increasing. Eliminate.
• Option B: Amplitude decreases, so energy (proportional to $A^2$) decreases. This matches the diagram.
• Option C: Energy depends on amplitude, not just wavelength. Amplitude changes, so energy isn’t constant. Eliminate.
• Option D: Peaks/troughs are normal for waves, but energy doesn’t “regularly increase/decrease” this way; amplitude decreases steadily. Eliminate.

Answer:

B. The energy of the wave decreases as shown by the decreasing amplitude.