Lenses - GRE Subject Test: Physics
Card 0 of 3
The focal length of a thin convex lens is 
. A candle is placed 
to the left of the lens. Approximately where is the image of the candle?
The focal length of a thin convex lens is
Because the object is beyond 2 focal lengths of the lens, the image must be between 1 and 2 focal lengths on the opposite side. Therefore, the image must be between 
on the right side of the lens.
Alternatively, one can apply the thin lens equation:
Where 
is the object distance 
and 
is the focal length 
. Plug in these values and solve.
Because the object is beyond 2 focal lengths of the lens, the image must be between 1 and 2 focal lengths on the opposite side. Therefore, the image must be between
Alternatively, one can apply the thin lens equation:
Where
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A candle 
tall is placed 
to the left of a thin convex lens with focal length 
. What is the height and orientation of the image created?
A candle
First, find the image distance 
from the thin lens equation:
Magnification of a lens is given by:
Where 
and 
are the image height and object height, respectively. The given object height is 
, which we can use to solve for the image height:
Because the sign is negative, the image is inverted.
First, find the image distance
Magnification of a lens is given by:
Where
Because the sign is negative, the image is inverted.
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Sirius is a binary star system, consisting of two white dwarfs with an angular separation of 3 arcseconds. What is the approximate minimum diameter lens needed to resolve the two stars in Sirius for an observation at 
?
Sirius is a binary star system, consisting of two white dwarfs with an angular separation of 3 arcseconds. What is the approximate minimum diameter lens needed to resolve the two stars in Sirius for an observation at
The Rayleigh Criterion gives the diffraction limit on resolution of a particular lens at a particular wavelength:
Where theta is the angular resolution in radians, 
is the wavelength of light, and 
is the diameter the lens in question. Solving for 
and converting 3 arcseconds into radians, one can approximate the diameter to be about 
:
The Rayleigh Criterion gives the diffraction limit on resolution of a particular lens at a particular wavelength:
Where theta is the angular resolution in radians,
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