Reflection and Refraction

Question 1

When does a mechanical wave reflect, absorb, or refract/transmission?

Answer 1

When a mechanical wave meets a new medium/new area of the same medium with different density or temperature.

Question 2

What is transmission?

Answer 2

The wave starts moving through the new medium.

Question 3

What is absorption?

Answer 3

The wave’s energy is absorbed by the new medium as heat.

Question 4

What is reflection?

Answer 4

The wave bounces off of the new medium.

Question 5

What is a wavefront?

Answer 5

Wavefronts are lines that correspond to the crest of the waves.
- When close to the source the wavefront is more curved
- When far away from the source the wavefront is nearly a straight line/less curved - called Plane Wavefront.

Question 6

What are rays?

Answer 6

Rays are arrows representing the direction of the wave and is drawn perpendicular to wavefronts.

Question 7

The Law of Reflection:

Answer 7

The incident angle is equal to the reflected angle. (θi = θr)

Question 8

Echo (Reflection):

Answer 8

When reflected waves of a sound reach your ear after more than 0.1 seconds apart.

Question 9

Reverberation (Reflection):

Answer 9

When reflected waves of a sound reach your ear after less than 0.1 seconds apart, your brain interprets the waves as a single sound.
- Excessive reverberation can make speech much harder to comprehend.

Question 10

when do sound waves travel faster?

Answer 10

-When the particles in the medium are closely packed.
-When the temperature is higher, the particles in the medium travel faster.
-Solid than liquid or gas.

Question 11

Why do waves refract?

Answer 11

Wavefronts refract because the plane wavefronts that first make contact with the new medium experience a change in velocity that causes it to bend away or towards the normal.

Question 12

What happens when a wave goes into a new medium?

Answer 12

• Frequency remains constant
• Velocity Changes
• Therefore wavelength changes because (v = ƒλ)

Question 13

How do sound waves refract when entering a hotter/denser medium?

Answer 13

• velocity and wavelength increases
• The wave will bend away from the normal ( θi < θr )

Question 14

How do sound waves refract when entering a cooler/less dense medium?

Answer 14

• Velocity and wavelength decreases
• The wave will bend towards the normal ( θi > θr )

Question 15

How is a temperature gradient created during the daytime?

Answer 15

Air closer to the ground gets warmed up, and air away from the ground stays relatively cooler. This creates a temperature gradient in which sound bends away from the ground.

Question 16

What is the critical angle?

Answer 16

Is the incident angle required for a sound wave’s angle of refraction to reach 90º. This causes the wave to meet both mediums simultaneously.
(θc)

Question 17

What is total internal reflection?

Answer 17

This is when the incident angle is greater than the critical angle, causing the reflected angle to be greater than 90º and in turn reflecting off of the new medium.
(θi >θc)

Question 18

Real-life applications of total internal reflection:

Answer 18

• Protects marine life from wind turbine noises
• Stethoscope mechanism

Question 19

Snell’s Law:

Answer 19

Describes the relation between the angle, velocity, and wavelength of a wave before and after it has been refracted.

sinθr/sinθr = vr/vi = λr/λi