Chapter 4 - Waves #2

Question 1

What is refraction?

Answer 1

The change of direction and speed of a wave when it crosses a boundary at an angle.

Question 2

What increases the amount by which waves spread out during diffraction?

Answer 2

The closer the gap is to the wavelength, the greater the amount of diffraction.

Question 3

What is superposition?

Answer 3

The effect of two waves adding together when they meet.

Question 4

What is a supercrest?

Answer 4

Where a crest meets a crest.

Question 5

What is a stationary wave?

Answer 5

A wave that oscillates in a fixed position.

The superposition of two progressive waves with the same frequency (and wavelength), moving in opposite directions.

Question 6

What is a progressive wave?

Answer 6

A wave which travels through a substance or through space if electromagentic.

Question 7

What is a minimum?

Answer 7

The resultant displacement when a crest meets a through of a different amplitude.

Question 8

What are nodes?

Answer 8

Points along a stationary wave where the displacement is always zero.

Question 9

What is interference?

Answer 9

The combination of two coherent progressive waves though superposition forming a resultant wave consisting of points of reinforcement (by constructive interference) and cancellation (by destructive interference).

Question 10

What is the fundamental mode of vibration (first harmonic)?

Answer 10

The stationary wave with the lowest possible number of nodes and thus lowest frequency.

Question 11

What are antinodes?

Answer 11

Points along a stationary wave that oscillate with maximum displacement.

Question 12

How are points of cancellation created?

Answer 12

When crests meet troughs and create gaps between wavefronts.

Question 13

What is the distance between adjacent nodes?

Answer 13

1/2λ

Question 14

What is the principle of superposition?

Answer 14

When two waves meet at a point, the total (resultant) displacement at that point is equal to the vector sum of the displacements of the individual waves.

Question 15

What are coherent waves?

Answer 15

Waves with the same frequency and constant (fixed) phase difference.
Using the same source is a good way of producing coherent waves.

Question 16

What are wavefronts?

Answer 16

Equally spaced lines of constant phase (e.g. peaks) with line spacing equal to wavelength.

The direction in which a wave travels is perpendicular to the wavefronts.

Question 17

What is diffraction?

Answer 17

The spreading out of waves when passing through a gap or travelling around an obstacle.

Question 18

What is path difference?

Answer 18

The difference between the distances from a point on an interference pattern to each source.

Question 19

Constructive interference occurs when…

Answer 19

…Path difference, d2 - d1 = nλ

Question 20

Destructive interference occurs when…

Answer 20

…Path difference, d2 - d1 = (n + 0.5)λ

Question 21

What is Young’s Double slit experiment?

Answer 21

The use of two coherent sources or the use of a single source with double slits to produce an interference pattern.

Question 22

What are Young’s fringes?

Answer 22

Alternate dark and bright fringes produced on a screen.

• A bright fringe corresponds to constructive interference.
• A dark fringe corresponds to destructive interference.

Question 23

What is a diffraction grating?

Answer 23

A plate with thousands of parallel and equally spaced slits.

Question 24

Two points are in phase if the phase difference is…

Answer 24

Two points are in phase if the phase difference is 0 or a multiple of 360° (a full cycle).

Question 25

Two points are exactly out of phase if the phase difference is…

Answer 25

…an odd-number multiple of 180° (π radians, a half-cycle).

Question 26

Two points are in phase if they are both at ___ _____ point in the wave cycle. Points in phase have the same ________ and ________.

Answer 26

Two points are in phase if they are both at the same point in the wave cycle. Points in phase have the same displacement and velocity.

Question 27

To get clear interference patterns, the two or more sources must be…

Answer 27

…coherent.

Question 28

What is intensity in the context of light?

Answer 28

The number of photons per second hitting a certain area.

Question 29

Why is the central maximum (bright fringe) in a single slit diffraction pattern the brightest?

Answer 29

Because the intensity of light is the highest in the centre.

Question 30

Learn how to derive diffraction grating equation!(Trigonometry!)
Look in CGP book for quick explanation.

Answer 30

Learn how to derive diffraction grating equation!
(Trigonometry!)
Look in CGP book for quick explanation.