Introduction to SAT II Physics - FreeExamPapers

As the diagram shows us, and as the two equations for lenses and mirrors will confirm,
the image is virtual, appears on the same side of the lens as the boy does, and stands
upright. This means that is negative and that and m are positive. Note that h > , so
m < 1.
Summary
There’s a lot of information to absorb about mirrors and lenses, and remembering which
rules apply to which kinds of mirrors and lenses can be quite difficult. However, this
information is all very systematic, so once you grasp the big picture, it’s quite easy to sort
out the details. In summary, we’ll list three things that may help you grasp the big
picture:
1. Learn to draw ray diagrams: Look over the diagrams of the four kinds of
optical instruments and practice drawing them yourself. Remember that light
refracts through lenses and reflects off mirrors. And remember that convex lenses
and concave mirrors focus light to a point, while concave lenses and convex
mirrors cause light to diverge away from a point.
2. Memorize the two fundamental equations: You can walk into SAT II
Physics knowing only the two equations for lenses and mirrors and still get a
perfect score on the optical instruments questions, so long as you know how to
apply these equations. Remember that f is positive for concave mirrors and
convex lenses, and negative for convex mirrors and concave lenses.
3. Memorize this table: Because we love you, we’ve put together a handy table
that summarizes everything we’ve covered in this section of the text.
Optical Instrument
Value
of d ´
Real or
virtual?
Value
of f
Upright or
upside down?
Mirrors ( and f are
positive in front of
mirror)
Concave d
> f
Concave d
< f
+ Real + Upside down
– Virtual + Upright
Convex – Virtual – Upright
Lenses ( and f are
positive on far side of
lens)
Convex d
> f
Convex d
< f
+ Real + Upside down
– Virtual + Upright
Concave – Virtual – Upright
Note that when is positive, the image is always real and upside down, and when is
negative, the image is always virtual and upright.
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