Ch. 15.3

Waves behave in predictable ways.

Vocabulary• reflection – the bouncing back of a wave

after it strikes a barrier• refraction – the bending of a wave as it

crosses the boundary between two mediums at an angle other than 90o

• diffraction – the spreading out of waves as they pass through an opening or around the edges of an obstacle

• interference – the meeting and combining of waves; the adding or subtracting of wave amplitudes that occurs as waves overlap

Review

• How are wavelength and frequency related?– As frequency increases,wavelength

will decrease and vice versa. Frequency is the number of waves (or wavelengths) that pass a fixed point in a certain amount of time.

Waves interact with materials

• Two examples of waves encountering a new medium:– Water wave hitting a wall– Sound wave moving from air to water

Reflection – Describe what happens when a water wave hits the wall of a

pool.• A water wave

transfers energy. When it arrives at a wall, it pushes against the wall. However, the wall applies an equal and opposite force, sending the wave back in the other direction. The wave is reflected.

Refraction

• Characteristics– Occurs because

of wave speed differences

• Examples– Light refracting as

it enters water

• Non-examples– Light reflecting

off a mirror

Refraction continued

• Based on your understanding of how refraction works, explain why there is no refraction when a wave enters a new medium at an exact 90-degree angle.

• Refraction occurs because one part of a wave enters the new medium before the other parts. The side of the wave that has entered the medium goes slower or faster than the rest of the waves and therefore the wave turns. At a 900 angle, all the parts of the wave will enter the medium at the same time

Diffraction

• The spreading out of waves through an opening or around the edge of an obstacle

• As a wave passes through an opening, it spreads out or diffraction occurs.

Interference• Characteristics:

– Can result in waves adding energy or subtracting energy from each other.

• Examples:– 2 sound waves interacting

with each other.

• Non-examples:– A wave refracting as it

enters a new medium

Constructive Interference

• It occurs when two waves overlap and their amplitudes add together.

Destructive Interference

• Happens when identical waves meet but are not aligned, such as sound waves from a stereo speaker.

• The waves add together in places and cancel in other places.