Question

light waves refract when they change ______
a speed
b energy
changes in the ______ of the medium through which a wave travels can cause the wave to either speed up or slow down.
a mass
b density
sound waves bending across a lake on a cold morning is an example of sound wave ______
a reflection
b refraction

Explanation:

• First question: Refraction of light waves occurs when their speed changes. For example, when light moves from air to water, its speed decreases, and it bends (refracts). Energy of light waves is related to their frequency (\(E = h

u\), where \(h\) is Planck's constant and \(
u\) is frequency) and not directly to refraction.

• Second question: The density of the medium affects the wave speed. According to wave - speed formula \(v=\sqrt{\frac{B}{

ho}}\) (for sound in a fluid, where \(B\) is the bulk modulus and \(
ho\) is density), a change in density (\(
ho\)) changes the speed. Mass alone (without considering the volume, as density is mass per unit volume) does not directly determine wave speed in the context of wave - medium interaction for speed change.

• Third question: Sound waves bending (like over a lake on a cold morning) is an example of refraction. Reflection would be the wave bouncing back (e.g., echo), while refraction is the bending due to a change in the medium (in this case, a change in air temperature which affects the air's properties and thus the sound wave speed).

Answer:

1. A. speed
2. B. density
3. A. refraction