What Is the Angle of Reflection in a Plane Mirror?

[Coco Hwang]

1) If the angle of incidence of a ray of light to mirror is 50 degrees, what is the angle of reflection from the mirror?

2) If the angle of incidence of a ray of light to a mirror is 20 degrees, what angle does the light ray make with the mirror when it reflects?

3) If a ray of light makes an angle of 58 degrees with a mirror, what is the angle between the incident ray and the reflected ray?The attempt - I'm having a hard time understanding the concept of mirrors, does the angle of reflection always equal to the angle of incidence?

Thank you!

 

[haruspex]

does the angle of reflection always equal to the angle of incidence?

Yes.

 

[Coco Hwang]

Yes.

thank you!

would this also apply for light rays?

 

[haruspex]

thank you!

would this also apply for light rays?

Also? What were we discussing if not light rays?

 

[Coco Hwang]

Also? What were we discussing if not light rays?

Sorry, I was not aware that angle of reflection and light rays were the same thing..

 

[haruspex]

Sorry, I was not aware that angle of reflection and light rays were the same thing..

They're not the same thing. Light rays are reflected in mirrors. The angle of reflection is an attribute of that reflection.
Although "reflection" generally refers to light, we can use the term in other contexts, figuratively.
But in the context of the present question, we are definitely discussing reflection of light rays.

 

[Coco Hwang]

They're not the same thing. Light rays are reflected in mirrors. The angle of reflection is an attribute of that reflection.
Although "reflection" generally refers to light, we can use the term in other contexts, figuratively.
But in the context of the present question, we are definitely discussing reflection of light rays.

Oh I see, thank you for your detailed response! So in this situation, would the answers for both questions #1 and #2 be the same as their angle of incidence?

 

[haruspex]

Oh I see, thank you for your detailed response! So in this situation, would the answers for both questions #1 and #2 be the same as their angle of incidence?

For #1, yes, but for #2 you need to think carefully about how the following are defined:

• Angle of incidence
• Angle of reflection
• Angle between the light ray and the mirror

 

[Coco Hwang]

For #1, yes, but for #2 you need to think carefully about how the following are defined:

• Angle of incidence
• Angle of reflection
• Angle between the light ray and the mirror

ok so for #2, would I subtract 20 degrees from 90 degrees? ( 70 degrees ) Or do I just multiply 20 two times ( 40 degrees )

 

[haruspex]

ok so for #2, would I subtract 20 degrees from 90 degrees? ( 70 degrees ) Or do I just multiply 20 two times ( 40 degrees )

One of those is correct. Which one and why?

 

[Coco Hwang]

One of those is correct. Which one and why?

Ummm, is it subtracting 20 from 90? Because the angle of incidence is 90 so I subtract the angle made from the reflection from it?

 

[haruspex]

Ummm, is it subtracting 20 from 90? Because the angle of incidence is 90 so I subtract the angle made from the reflection from it?

Yes, but why? How is the angle of reflection defined, geometrically? How is that different from the angle the reflection makes to the mirror?