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  • Intro 0:00
  • Question 1 0:12
  • Question 2 0:50
  • Question 3 1:29
  • Question 4 1:46
  • Question 5 3:08

Transcription: Reflection

Hi everyone and welcome back to

In this mini-lesson, we are going to go through page 1 of the APlusPhysics worksheet on reflection and you can find a link to that worksheet down below the video.0002

Number 1 -- The diagram below represents a light ray striking a boundary between air and glass.0011

What would be the angle between this light ray and its reflected ray?0017

Well, first let us remember that we have to measure the angle of incidence to the normal, so if that is 30 degrees, this must be 60 degrees and our reflected ray, then, should look something, kind of like that and its angle of reflection is equal to the angle of incidence, 60 degrees.0021

So the total angle there between the incident ray and the reflected ray is 120 degrees -- Answer 3.0040

Number 2 -- The diagram below represents a view from above of a tank of water in which parallel wave fronts are traveling toward a barrier.0050

Which arrow represents the direction of travel for the wave fronts after being reflected from the barrier?0058

Well first thing I am going to do again is, I am going to draw the normal to my surface, so it looks like the normal is actually here on (B).0064

If we have (V) coming in, its angle of incidence is here between (A) and (B); its angle of reflection must be the same between (B) and (C), so I would say that C is our best answer for the reflected ray.0072

Number 3 -- A sonar wave is reflected from the ocean floor.0089

For which angles of incidence do the wave's angle of reflection equal its angle of incidence?0093

Well, we call it the law of reflection for a reason.0098

That is going to work for all angles of incidence.0101

Number 4 -- Two plane mirrors are positioned perpendicular to each other as shown.0106

A ray of monochromatic red light comes in here with an angle of incidence of 55 degrees and it's reflected from mirror 1 and then onto mirror 2, where it is reflected again.0112

Determine the angle at which the ray is incident on mirror 2 and label the angle on the diagram in degrees.0123

All right, so if this is 55 degrees right here, we must have 55 degrees here and we will also draw in our normal to mirror 2 and as I look, if this is 55 degrees and that is a right triangle 55, then that must be 90, and that means our angle right here must be 35 degrees.0131

For our angle of reflection, I should draw with a nice protractor, and show that that is going that direction and it, too, must have an angle of 35 degrees.0155

So determine the angle at which the ray is incident on mirror 2.0169

That is going to be our answer of 35 degrees and use a protractor and straight-edge to draw the ray of light as it is reflected from mirror 2.0172

Well, I will leave it to you to use a protractor, but it should be at the same angle as that angle of incidence on mirror 2.0179

One more here -- The diagram below represents a light ray reflecting from a plane mirror.0187

The angle of reflection for the light ray is -- well, let us draw our normal.0192

If it is incident at 65 degrees and this whole angle is 90, that means this angle must be 25 degrees.0199

Well, if that is the case, then the reflected angle must also be 25 degrees.0206

The angle of reflection is Number 1, 25 degrees.0211

All right, that completes page 1 of the reflection worksheet.0215

If this went well -- Terrific -- Go ahead and keep moving on and if you struggled with this, it is probably a great time to go review the entire lesson on reflection.0219

Thanks everyone and make it a great day!0227