Waves 2

Question 1

What is diffraction?

Answer 1

The spreading out of waves as they pass through a narrow gap or around obstacles.

Question 2

What factors affect the amount of diffraction?

Answer 2

The size of the gap in comparison to the wavelength of the wave.

Question 3

What is a ripple tank used for?

Answer 3

To investigate diffraction by generating waves and observing their behavior when encountering barriers.

Question 4

What happens when the gap is much bigger than the wavelength?

Answer 4

Diffraction is unnoticeable.

Question 5

When does maximum diffraction occur?

Answer 5

When the gap size is approximately equal to the wavelength.

Question 6

What occurs when the gap decreases in size?

Answer 6

Diffraction becomes more noticeable until the gap is too small for waves to pass through, resulting in reflection.

Question 7

Why can you hear someone through an open doorway?

Answer 7

Because the size of the gap and the wavelength of sound are roughly equal, allowing significant diffraction.

Question 8

Why can’t you see someone through a doorway?

Answer 8

Light passing through the doorway has a gap much larger than its wavelength, resulting in minimal diffraction.

Question 9

How can diffraction in light be demonstrated?

Answer 9

By shining laser light through a very narrow slit onto a screen.

Question 10

What happens when you alter the width of the slit in a light diffraction experiment?

Answer 10

The amount of diffraction changes.

Question 11

What is created when waves meet an obstacle?

Answer 11

Diffraction around the edges and a shadow behind the obstacle.

Question 12

What is the effect of the obstacle size on diffraction?

Answer 12

The wider the obstacle compared to the wavelength, the less diffraction and the longer the shadow.

Question 13

What does a diffraction pattern of light and dark fringes indicate?

Answer 13

It indicates that the wavelength of light is similar to the size of the aperture.

Question 14

What is the angle of incidence?

Answer 14

The angle the incoming waves make with the normal to the barrier.

Question 15

What is the angle of reflection?

Answer 15

The angle between the direction of the reflected waves and the normal to the barrier.

Question 16

What relationship exists between the angle of incidence and the angle of reflection?

Answer 16

The angle of incidence always equals the angle of reflection.

Question 17

Fill in the blank: Reflection means the wave is ______ when it hits a boundary.

Answer 17

[bounced back]

Question 18

What is observed when a barrier is placed at an angle to the wave fronts in a ripple tank?

Answer 18

Waves reflect off the barrier and travel in a different direction.

Question 19

What happens to the angle of reflection when the angle of incidence changes?

Answer 19

The angle of reflection changes by the same amount.

Question 20

What occurs when the medium a wave is traveling in changes?

Answer 20

Refraction

Refraction is the way a wave changes direction as it enters a different medium.

Question 21

What happens to a light ray when it bends towards the normal?

Answer 21

It is slowing down and going from a less optically dense to a more optically dense material.

Question 22

What happens to a light ray when it bends away from the normal?

Answer 22

It is speeding up and going from an optically denser material to a less optically dense material.

Question 23

What causes the speed change of light when it enters a different medium?

Answer 23

The wavelength of the wave changes while the frequency remains constant.

Question 24

What is the absolute refractive index of a material?

Answer 24

The ratio between the speed of light in a vacuum (c) and the speed of light in that material (v).

Question 25

What is the refractive index of air assumed to be?

Answer 25

1 ## Footnote The speed of light in air is only a tiny bit smaller than in a vacuum.

Question 26

What does Snell's Law express?

Answer 26

n₁ sin θ₁ = n₂ sin θ₂ ## Footnote Where n is the refractive index and θ is the angle of incidence or refraction.

Question 27

What does the equation n sin θ = constant imply?

Answer 27

That n₁ sin θ₁ = n₂ sin θ₂ at any boundary.

Question 28

What phenomenon occurs when the angle of incidence exceeds the critical angle?

Answer 28

Total internal reflection.

Question 29

What happens at the critical angle?

Answer 29

The angle of refraction is 90° and light is refracted along the boundary.

Question 30

How can you investigate critical angles and total internal reflection?

Answer 30

By shining a light ray into a curved face of a semi-circular glass block.

Question 31

What is the critical angle for a material-to-air boundary?

Answer 31

It can be calculated using the formula sin C = 1/n ## Footnote Where n is the refractive index of the material.

Question 32

What occurs when the angle of incidence is less than the critical angle?

Answer 32

The ray is partially refracted and partially reflected.

Question 33

What happens when the angle of incidence equals the critical angle?

Answer 33

The light ray is refracted along the boundary.

Question 34

What do you observe when increasing the angle of incidence beyond the critical angle?

Answer 34

The ray is reflected from the straight edge of the block.

Question 35

Fill in the blank: The speed of light is fastest in a _______.

Answer 35

vacuum.

Question 36

What happens when two waves meet?

Answer 36

The displacements due to each wave combine, and then each wave continues on its own path.

Question 37

What does the principle of superposition state?

Answer 37

The resultant displacement equals the vector sum of the individual displacements.

Question 38

What is constructive interference?

Answer 38

When two waves superpose to create a larger wave, such as a crest plus a crest or a trough plus a trough.

Question 39

What is destructive interference?

Answer 39

When a crest and a trough of equal size cancel each other out completely.

Question 40

What is required for noticeable destructive interference?

Answer 40

The two amplitudes should be nearly equal.

Question 41

What does 'in phase' mean?

Answer 41

Two points are in phase if they are at the same point in the wave cycle, having the same displacement and velocity.

Question 42

What is the phase difference for points to be in phase?

Answer 42

A phase difference of zero or a multiple of 360°.

Question 43

What is the phase difference for points to be out of phase?

Answer 43

Odd-number multiples of 180°.

Question 44

What is coherence in wave sources?

Answer 44

Two sources are coherent if they have the same wavelength, frequency, and a fixed phase difference.

Question 45

What determines whether interference is constructive or destructive?

Answer 45

The path difference between the waves at a point.

Question 46

What is the path difference for constructive interference?

Answer 46

Path difference = nλ (where n is an integer).

Question 47

What is the path difference for destructive interference?

Answer 47

Path difference = (2n + 1)λ/2 = (n + ½)λ.

Question 48

How can you observe interference with sound waves?

Answer 48

By connecting two coherent speakers and walking across the room to hear varying volumes of sound.

Question 49

What happens at points of loudest sound when observing interference?

Answer 49

The path difference is a whole wavelength.

Question 50

What happens at points of quietest sound when observing interference?

Answer 50

The path difference is an odd number of half wavelengths.