Final answer:
The brightness or loudness of points in a wave-propagated energy, such as sound, is determined by the wave's amplitude. Higher amplitude indicates greater intensity and is perceived as increased brightness for light or loudness for sound.
Step-by-step explanation:
Points whose brightness depends on the amplitude of the returning sound energy are crucial in understanding the relationship between wave amplitude and perceived intensity. The intensity of a wave-propagated energy is directly related to the amplitude of the wave. In the context of light, this is perceived as luminous intensity, or brightness, and in the context of sound, it is perceived as loudness. For instance, an ultrasound speaker emits sound waves, and the returning echoes provide information about the reflector's distance. The brightness or loudness of these points is greater when the wave amplitude is larger, which indicates higher pressure maxima and minima. Hence, wave amplitude affects the intensity of the sound, making the sound exert larger forces on objects, which relates to higher perceived loudness.