12.2

Question 1

What is an interference pattern

Answer 1

Pattern of constructive and destructive interference formed as waves overlap

Question 2

What is coherence

Answer 2

• Waves emitted from two sources have a constant phase difference
• Waves must have same frequency

Question 3

What is a maxima

Answer 3

• The point of greatest amplitude in an interference pattern

-produced by constructive interference

Question 4

What is a minima

Answer 4

• The point of least amplitude in an interference pattern

-produced by destructive interference

Question 5

What is path difference

Answer 5

• The difference in the distance travelled by two waves from their source to a specific point
• Measured in wavelengths

Question 6

What is phase difference

Answer 6

• Difference between the displacements of particles/points along a wave
• Or difference between the displacements of particles/points on different waves
• Measured in degrees or radians, with each complete cycle or a difference of one wavelength representing 2pi radians (360°)

Question 7

What is the result of a path difference which is an integer multiple of the wavelength

Answer 7

• Two waves will arrive at that point in phase
• This produces constructive interference at that point
• Waves at this point has maximum amplitude

Question 8

What is the result of a path difference which is NOT an integer multiple of the wavelength

Answer 8

• Two waves will arrive at that point in antiphase
• This produces destructive interference at that point
• Waves at this point has minimum amplitude

Question 9

What is at the central maxima

Answer 9

• Path difference is zero

* Phase difference is zero

Question 10

What is at the first-order maxima

Answer 10

• Path difference is one wavelength
• Phase difference is 360° / 2pi radians
• Constructive interference occurs

Question 11

What is at the first-order minima

Answer 11

• Path difference is half a wavelength
• Phase difference is 180° / pi radians
• Destructive interference occurs

Question 12

How is interference in sound studied

Answer 12

• Two loudspeakers connected to same signal generator (coherent) emit sound waves

• Sound waves travel out from each loudspeaker and overlap (superpose)
-forms interference pattern

• Interference pattern compromises a series of maxima [louder] and minima [quieter]
• Positions of maxima and minima can be detected with ears (or more accurately microphone)

Question 13

How is interference in microwaves studied

Answer 13

• Single microwaves source is used with pair of slits [double slit]
-coherent

• Diffracted microwaves overlap (superpose)

• Interference pattern formed
-detected with microwave receiver connected to voltmeter or oscilloscope

• Moving receiver in arc around double slits detects the characteristic maxima and minima created as part of interference pattern
-position of each can be carefully marked on paper