Physical Science B lesson 16 Characteristics of Waves

Diffraction

Diffraction is the bending of waves when they pass through small spaces or around obstacles. Both mechanical waves and electromagnetic waves can diffract. Water waves that approach a small opening as straight lines will bend into a fairly uniform arching pattern as they pass through. When the waves travel through two small openings, the bent waves form two concentric arcs that begin to interfere with each other, forming a more complex pattern. The larger the wavelength and the smaller the opening the greater the bending.

Study the scenario. Milo and a friend hold opposite ends of a long toy spring. Milo compresses a few of the coils and then lets go, while Milo's friend keeps the other end of the spring held tight. Which of the following choices best describes what is happening with the spring's energy?

Energy moves from Milo's end to the opposite end as a wave. The different parts of the spring do not travel to the opposite end.

Reverberation

In a large, empty auditorium, the waves are reflected in a number of directions, as they spread out in different directions from their source. Since not all paths to where the sound is heard are the same length, sound waves from different points in time arrive mixed together. This can cause multiple echoes. This mixture of multiple sound waves reflected off different surfaces is known as reverberation. Sound studios pad their walls with sound-absorbing materials to prevent reverberation.

A wave is capable of travelling through a solid or a gas, which of the following best describes the wave?

The wave can be a longitudinal or transverse wave because both types of waves can travel through solids and gases.

Two transverse waves are moving towards each other. What happens when the crest of one wave overlaps with the trough of the other wave?

destructive interference

amplitude

distance from the equilibrium position to the peak of the crest or the trough

The change in a wave's direction when it encounters a surface and bounces back is known as

reflection

What behavior causes these straws to appear broken at the water line?

refraction

refraction

the bending of a wave when it enters a different medium

reverberation

the mixture of multiple sound waves reflected off different surfaces

period

the time required for one complete cycle of a wave to occur

A wave is detected travelling through the vacuum of deep space. What type of wave must this be?

transverse wave

Interference

When waves encounter other waves, they can interfere with each other. Interference is a change in amplitude that occurs when two waves of the same type intersect each other and combine. There are two basic kinds of interference in waves. Constructive interference occurs when the crossing waves are in phase, or when the crest or trough of one wave superposes (stacks up on) the crest or trough of another wave. Destructive interference occurs when waves are out of phase, or when the crest of one wave and the trough of another meet and cancel each other out. A film of oil in a puddle or on a body of water creates a rainbow-like spectrum because of light wave interference. Noise-cancelling devices have been created to produce out of phase waves to diminish the strength of unwanted sounds.

interference

a change in amplitude that occurs when two waves of the same type intersect each other and combine

wave

a disturbance that transmits energy from one location to another without transporting matter

diffraction

the bending of waves when they pass through small spaces or around obstacles

reflection

the change in a wave's direction when it bounces off the surface of a different medium

Which of the following describes the difference between a transverse wave and a longitudinal wave?

the direction in which the particles in the medium move

wavelength

the distance along a wave from a point in one crest to the same point in the next crest, or trough to trough

frequency

the number of complete cycles of a wave that occur in a second

Law of Reflection

1. The incident wave is the wave that strikes the reflecting material. So the angle of incidence is the angle at which the wave strikes the surface, relative to a line perpendicular to the surface plane. This line is called the normal. 2. The reflected wave is the wave that leaves the surface of the reflecting material. The angle of reflection is the angle at which the wave departs the surface, relative to the normal. 3. The angle of reflection equals the angle of incidence.

Refraction

Refraction is the bending of a wave when it enters a different medium. This occurs because of a change in speed of the wave in the new medium, compared to its speed in the previous medium. The change in speed will cause a change in the wavelength of the wave. The direction that the wave bends usually depends on whether the new medium is more or less dense than the one the wave is leaving. If the new medium is denser than the one wave comes from, the wave will slow down and bend towards the normal. If the new medium is less dense, the wave will speed up and bend away from the normal. This can happen to electromagnetic or mechanical waves.

Standing Waves

Standing waves are the result of two waves with the same amplitude and frequency that encounter each other traveling in opposite directions. The resulting interference creates a pattern that appears to be frozen in place. Standing waves are often the result of the result of a wave being reflected back on itself. The result is seen below, where the waveform result is stationary. The part of the wave where there is no energy or amplitude is called a node and the part of the wave that has maximum energy is called the antinode. Standing waves occur in some everyday situations. For example, when playing jump rope, if the person at each end of the rope can synchronize the vibration of the rope just right, the result is a standing wave.