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### Diffraction

Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.

• Intro 0:00
• Question 1 0:16
• Question 2 0:31
• Question 3 0:50
• Question 4 1:05
• Question 5 1:37
• Question 6 2:04

### Transcription: Diffraction

Hi everyone and welcome back to Educator.com0000

I am Dan Fullerton and in this mini-lesson, we are going to go through page 1 of the APlusPhysics worksheet on diffraction.0003

Just looking at a quick qualitative or conceptual understanding of diffraction.0009

Let us dive right in.0014

Question Number 1 -- A wave of constant wave length diffracts as it passes through an opening in a barrier.0016

As the size of the opening is increased, the diffraction effects -- well the diffraction effects here are going to decrease.0021

Number 2 -- The diagram below shows a series of wave fronts approaching an opening in a barrier.0031

Point (P) is located on the opposite side of the barrier0036

The wave fronts reach point (P) as a result of -- well the only way they can get there is by bending around the opening.0039

That is what we call diffraction.0045

Number 3 -- Which wave phenomenon makes it possible for a player to hear the sound from a referee's whistle in an open field even when standing behind the referee?0047

Of course, the answer there is also refraction.0057

The sound is bending around the referee.0061

Number 4 -- A wave is diffracted as it passes through an opening in a barrier.0064

The amount of diffraction that the wave undergoes depends on both the amplitude and frequency? -- No, not amplitude and frequency...0069

... wave length and speed of the incident wave -- No...0077

...3 -- wave length of the incident wave and the size of the opening -- Now we are talking.0082

There is our answer -- An amplitude of the wave and size of the opening? -- No, it is wavelength of the incident wave and the size of the opening.0086

So the correct answer there is Number 3.0093

Number 5 -- The diagram below shows a plane wave passing through a small opening in a barrier.0098

On the diagram sketch four wave fronts after they have passed through the barrier.0102

Well the wave fronts are going to bend as they go through that barrier, so we are going to get something that looks probably kind of like that.0106

One way to remember that is if the wave is traveling to the right, you almost get that shape of a (D) for diffraction.0116

All right last one.0121

Which diagram best represents the shape and direction of a series of wave fronts after they have passed through a small opening in a barrier?0124

Well, we basically just did this one, so that must be answer 4.0133

Just a qualitative look at diffraction is a first pass check to see if you have the basics down.0138

If this did not go well, then it is a great chance to go to review the diffraction lesson and if it did go well, you are probably ready to move on to the harder AP level questions.0145

Thanks so much for you time and make it a great day everyone.0151