Concave vs Convex, Mirrors vs Lenses

[sunflower18]

Let me see if I have this correct.

Concave Mirrors:
- if object is farther away from the mirror than its focal point, the object is real, inverted, and smaller than the object
- if object is closer to the mirror than its focal point, the object is virtual, upright, and larger than the object
What if the object is AT the focal point exactly?

Convex Mirrors:
- the image is virtual, upright, and smaller than the object (always?)

Concave Lenses:
- the image is real, upright, and smaller than the object??

Convex Lenses:
- the image is virtual, inverted, and gets smaller as you move away from the focal point?
Does it matter if you are closer to the lens than its focal point?

Okay, so I am totally confused. All these terms and conventions are just extremely confusing to me. I know that 1/o + 1/i = 1/f, and that m = -i/o. But it's hard for those equations to be helpful when I don't know what conventions mean what!

Thanks 🙂

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[gettheleadout]

Let me see if I have this correct.

Concave Mirrors:
- if object is farther away from the mirror than its focal point, the object is real, inverted, and smaller than the object
- if object is closer to the mirror than its focal point, the object is virtual, upright, and larger than the object
What if the object is AT the focal point exactly?

For concave mirrors it's more complicated because you have the radius of curvature to worry about: http://www.wikipremed.com/01physicscards.php?card=846

Convex Mirrors:
- the image is virtual, upright, and smaller than the object (always?)

Yep, always. Also, the image is always inside the focal length

Concave Lenses:
- the image is real, upright, and smaller than the object??

Yep. Same deal as with the convex mirror as well, the image is always inside the focal length.

Convex Lenses:
- the image is virtual, inverted, and gets smaller as you move away from the focal point?
Does it matter if you are closer to the lens than its focal point?

Not that simple at all, unfortunately. Would recommend you see here: http://www.wikipremed.com/01physicscards.php?card=854

and play with this: http://phet.colorado.edu/sims/geometric-optics/geometric-optics_en.html

Be sure to turn on virtual image.

Okay, so I am totally confused. All these terms and conventions are just extremely confusing to me. I know that 1/o + 1/i = 1/f, and that m = -i/o. But it's hard for those equations to be helpful when I don't know what conventions mean what!

For sign convention, know this: object distance is always positive, and the sign of any other distance is based on the optical axis; the zero of the axis is at the optical element (lens or mirror) and runs positive in the direction of light exiting the optical system, and negative the opposite direction.

Thanks 🙂

Hope that helps!

 

[onedirection]

Object at focal length, there is no image for a concave mirror

 

[gettheleadout]

Object at focal length, there is no image for a concave mirror

Also known as "real image at infinity." This could be given as a valid answer choice as well.

 

[sunflower18]

Hope that helps!

Object at focal length, there is no image for a concave mirror

Thanks so much you guys!! I really appreciate it. Definitely helpful.

 

[sunflower18]

That flash animation moving the images around thing has been EXACTLY what I've been looking for. I'm definitely a visual learner, which I didn't know before I began studying for this test, hah. Thanks so much!!!

 

[gettheleadout]

That flash animation moving the images around thing has been EXACTLY what I've been looking for. I'm definitely a visual learner, which I didn't know before I began studying for this test, hah. Thanks so much!!!

Same haha, I couldn't find one for mirrors, so I ended up using a real makeup mirror (concave mirror) to physically move along the optical axis.

Glad I could help!

 

[sunflower18]

Same haha, I couldn't find one for mirrors, so I ended up using a real makeup mirror (concave mirror) to physically move along the optical axis.

Glad I could help!

Oooh that's a good idea! 👍👍 Thanks so much again!