# Quick question on mirror and lens scenario

1. Aug 26, 2014

### hongiddong

I attached a picture with 3 questions?

My first question is, I know that for a convex or concave mirror, If I shine a light at an angle to the middle of the mirror the light will reflect with the same angle. Will the angle be the same if I shine the light at the concave/convex mirror if it is not in the middle, when the light is not at the focal points, or parallel?

My second and third questions are related, for a diverging and converging lens, if I have the object in ront of the focal point, and the light is shining diagonally away from the focal point, will the light refract into the lens parallel?

The drawings should help elucidate!

Thank you!

#### Attached Files:

• ###### Lense question.png
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2. Aug 27, 2014

### Drakkith

Staff Emeritus
Shining the light at an off center part of the mirror would make the ray reflect at a different angle than shining it at the center of the mirror. That's precisely how mirrors and lenses work to converge or diverge light.

Placing an object closer to the lens than the focal point would make the light diverge after being refracted through the lens instead of being parallel.

3. Aug 27, 2014

### CWatters

The simple answer is that light is always reflected at the same angle from a mirror....

#### Attached Files:

• ###### Mirror.png
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4. Aug 27, 2014

### Drakkith

Staff Emeritus
That's only true for a flat mirror. Two parallel rays hitting a curved mirror will reflect at different angles if they hit in different locations.

5. Aug 27, 2014

### Staff: Mentor

From the diagram to which he added the reflected rays, I'm pretty sure that "always reflected at the same angle" was supposed to mean "always reflected at the same angle as it came in, at that point", i.e. angle of reflection = angle of incidence at each point of reflection.

6. Aug 27, 2014

### hongiddong

For the diverging lens, if the object was infront of the focal point, and the light is hitting it as shown in my picture, would then the refracting light continue to refract away in the same direction from the focal point instead of going parallel?

Lastly, what would happen to a converging lens for the same scenario in which the object is infront of the focal point?

7. Aug 27, 2014

### Drakkith

Staff Emeritus
Oh I'm sorry, I didn't realize that was a diverging lens. In that case, the light will always be diverging after passing through the lens, no matter where you place the object. In your picture you have the light refracting the wrong way.

For a converging lens the rays will be refracted to parallel with each other if the object is located at the focal point, they will diverge if the object is closer to the lens than the focal point, and will converge if the object is farther from the lens than the focal point.

8. Aug 27, 2014

### hongiddong

Thanks everyone. I understand the problem now

9. Aug 28, 2014

### CWatters

You misunderstand what I meant.

Clearly two different rays hitting a curved mirror at different locations will reflect at different angles BUT each will still be reflected at the same angle it arrived at. The angle of incidence is always the same as the angle of reflection.

10. Aug 28, 2014

### Drakkith

Staff Emeritus
Oh, you mean the angle of the ray compared to the mirror's surface. Gotcha.