Wave behaviours—reflection, refraction and diffraction

Question 1

Mechanical waves transfer energy through a medium, but there will be times when that medium physically ends. A change in the physical characteristics in the same medium, such as density and temperature, can act like a change in medium. When the medium ends, or changes, the wave doesn’t just stop. Instead, the energy that the wave is carrying will:

Answer 1

Reflection
Refraction
Absorption

Question 2

Reflection

Answer 2

When a transverse wave pulse reaches a hard surface, the wave is bounced back or reflected.

Question 3

Reflection characteristic

Answer 3

Wave pulse moves along string and hits post
String exerts upwards force on post
Due to newtons third law, the fixed post exerts equal opposite force on string which inverts the pulse and sends its reflection back to left on bottom side of string

Question 4

Free Boundary

Answer 4

When a wave pulse hits the end of a rope thats free to move, the pulse returns with no change of phase, reflected pulse is same as incident pulse

Question 5

When the transverse wave pulse is reflected, the amplitude of the reflected wave is not the same as the original, why?

Answer 5

Part of the energy of the wave is absorbed by the post and some is transformed into heat energy and some travels through the post

Question 6

When a transfer wave pulse is sent from a light rope to a heavy rope

Answer 6

Part of the wave is reflected and part is transmitted to heavier rope
As the second rope is heavier, a smaller part is transmitted and more is reflected back

Question 7

The more rigid and/or dense a wall is

Answer 7

the more energy will be reflected and less is absorbed (some energy will always be absorbed or transferred to the second medium)

Question 8

Wave fronts

Answer 8

when close to source = curved
when far from source = straight = plane wave

Question 9

Ray

Answer 9

The direction of motion of any wave front can be represented by a line drawn perpendicular to the wave front and in the direction the wave is

Question 10

Law of reflection

Answer 10

The law of reflection states that the angle of reflection (θr), measured from the normal, equals the angle of incidence (θi) measured from the normal
θi = θr

Question 11

Law of reflection is true for an surface whether its

Answer 11

straight, curved or irregular, normal is drawn perpendicular to the surface at the point of contact of the rays

Question 12

diffuse reaction

Answer 12

when wave fronts meet an irregular , rough surface, the resulting reflection can be spread over a broad area bc each point on the surface reflects the portion of the wave front reaching it in a diff direction

Question 13

echo

Answer 13

when a sound wave thats reflected at a wall reaches us in a delayed time, u can hear an echo and its heard as a seperate sound

Question 14

reverberation

Answer 14

in smaller rooms, the waves are reflected several times at diff walls and they overlap and produce reverberation which sounds like a longer sound

Question 15

echoes typically occur in

Answer 15

large rooms with bare walls and hard surfaces

Question 16

how to reduce echo (acoustic engineering)

Answer 16

acoustic foam sheets, rugs, textiles on wall to absorb sound and objects to diffuse the reflections of the sound waves

Question 17

refraction

Answer 17

when a wave crosses the boundary and theres a change in velocity and wavelnegth, the transmitted wave travels in a different direction to the original wave

Question 18

why do wave fronts refract

Answer 18

the part of the wave front that reaches the boundary first slows down (or speeds up) while the remainder of the wave front still in the original medium continues at its original speed

Question 19

speed of sound depends on

Answer 19

stiffness and elasticity
(inertia or density)

Question 20

elasticity

Answer 20

a measure of the tendency of a medium to return to its original shape after it has been bent compressed or stretched

Question 21

when a sound propagates through a medium in a series of compression and rarefactions (longitudinal)

Answer 21

it travels faster in a more elastic medium
solid -> liquid -> gas

Question 22

if theres a change in state as a sound wave travels from one medium to the next

Answer 22

there will be a significant effect on the speed

Question 23

density

Answer 23

the more dense the medium is, the slower the speed because the greater mass per unit volume makes it more difficult for a given force to move the medium so the vibrations take more time

Question 24

temperature

Answer 24

increasing temp, reduces density (no change elasticity), increases speed of sound
decreasing temp, increase density, decreasing speed of sound
refraction can occur between hot and cold medium

Question 25

refraction of sound when entering hotter medium (wave front speed up)

Answer 25

v2 > v1
λ2 > λ1
f2 = f1
∠r > ∠i

Question 26

refraction of sound when entering colder medium

Answer 26

v1 > v2
λ1 > λ2
f1 = f2
∠i > ∠r