Chapter 17.2- The interference of light Flashcards
What is interference?
When waves interact
What is constructive interference?
When the inference of waves leads to a larger amplitude
What is destructive interference?
When the interference of waves leads to a smaller or even zero amplitude
What do we use to create light scenarios where we see diffraction patterns?
Very small slits and ray beams
What do we use to create light scenarios where we can see the interference of light?
We have to use double slits and a ray of light
What are double slits?
Two long narrow slits that are close together. Used to see interference of light
What do double slits do when light is seen through them?
The light spreads out behind each slit. The two spreading waves of light overlap in the region between the slits and the screen
Where does constructive interference occur?
When the distances between r1 and r2 differ by JUST a WHOLE NUMBER of wavelengths
Where does destructive interference occur?
When the distances between r1 and r2 differ by a whole number of wavelengths AND A HALF
What is m
m is just an integer used to measure the difference of wavelengths
What will we see for constructive interference?
The intensity of light to be high
What will we see for destructive interference?
For these positions on the screen to be completely dark
What are interference fringes?
A series of alternating bright and dark bands
What is the central maximum?
When m = 0 and it is the brightest fringe. It is the midpoint of the viewing screen.
Geometry of the double-slit interference:
What is d
The spacing between the two slits
Geometry of the double-slit interference:
what is L
The distance to the viewing screen
Geometry of the double-slit interference:
What do we assume in relation between L and d
We assume that L is MUCH LARGER than d
Geometry of the double-slit interference:
How do we calculate change in r besides the obvious way
Multiply the integer thing, m, by lambda. IF ITS CONSTRUCTIVE INTERFERENCE.
Geometry of the double-slit interference:
How do we find the specific positions not the screen where constructive interference occurs and change in r = m(lamda)
Y = L tan theta
Geometry of the double-slit interference:
What is P
The distance of r1 from one slit and r2 from the other slit
Geometry of the double-slit interference:
How can we calculate point P
By either finding y or by finding angle theta
Geometry of the double-slit interference:
What is y
Distance from the center of the viewing screen
Geometry of the double-slit interference:
How can we find y
y = L tan theta
y = (m lambda L / d )
Geometry of the double-slit interference:
Because the screen is very far away compared to the distance between the two slits what are the two things we can assume
- That the two paths to point P are virtually parallel
2. Because they are parallel, we can make a small right triangle who has angle theta
Geometry of the double-slit interference:
What is the path length difference between the two waves
The short side of the small right triangle.
Geometry of the double-slit interference:
What is theta m
Angle theta of bright fringes
Geometry of the double-slit interference:
What is y’m
The mth minimum
Geometry of the double-slit interference:
What is ym
The mth maximum
Geometry of the double-slit interference:
What did you get confused about on example 17.2
I thought that when it said a bright fringe is observed at 9.5 mm that it was r1. But it wasn’t I needed to plug it into equation 17.8 for bright fringes
