The eyes of amphibians such as frogs havea much flatter cornea but a more strongly curved (almost spherical)lens than do the eyes of air-dwelling mammals. In mammalian eyes,the shape (and therefore the focal length) of the lens changes to enablethe eye to focus at different distances. In amphibian eyes, the shapeof the lens doesn’t change. Amphibians focus on objects at differentdistances by using specialized muscles to move the lens closer to orfarther from the retina, like the focusing mechanism of a camera. In air,most frogs are nearsighted; correcting the distance vision of a typicalfrog in air would require contact lenses with a power of about -6.0 D. To determine whether a frog can judge distance by means of the amount its lens must move to focus on an object, researchers covered one eye with an opaque material. An insect was placed in front of the frog, and the distance that the frog snapped its tongue out to catch the insect was measured with high-speed video. The experiment was repeated with a contact lens over the eye to determine whether the frog could correctly judge the distance under these conditions. If such an experiment is performed twice, once with a lens of power -9 D and once with a lens of power -15 D, in which case does the frog have to focus at a shorter distance, and why? (a) With the -9 D lens; because the lenses are diverging, the lens with the longer focal length creates an image that is closer to the frog. (b) With the -15 D lens; because the lenses are diverging, the lens with the shorter focal length creates an image that is closer to the frog. (c) With the -9 D lens; because the lenses are converging, the lens with the longer focal length creates a larger real image. (d) With the -15 D lens; because the lenses are converging, the lens with the shorter focal length creates a larger real image.
The eyes of amphibians such as frogs have
a much flatter cornea but a more strongly curved (almost spherical)
lens than do the eyes of air-dwelling mammals. In mammalian eyes,
the shape (and therefore the focal length) of the lens changes to enable
the eye to focus at different distances. In amphibian eyes, the shape
of the lens doesn’t change. Amphibians focus on objects at different
distances by using specialized muscles to move the lens closer to or
farther from the retina, like the focusing mechanism of a camera. In air,
most frogs are nearsighted; correcting the distance vision of a typical
frog in air would require contact lenses with a power of about -6.0 D. To determine whether a frog can judge distance by means of
the amount its lens must move to focus on an object, researchers covered
one eye with an opaque material. An insect was placed in front
of the frog, and the distance that the frog snapped its tongue out to
catch the insect was measured with high-speed video. The experiment
was repeated with a contact lens over the eye to determine whether
the frog could correctly judge the distance under these conditions. If
such an experiment is performed twice, once with a lens of power
-9 D and once with a lens of power -15 D, in which case does the
frog have to focus at a shorter distance, and why? (a) With the -9 D
lens; because the lenses are diverging, the lens with the longer focal
length creates an image that is closer to the frog. (b) With the -15 D
lens; because the lenses are diverging, the lens with the shorter focal
length creates an image that is closer to the frog. (c) With the -9 D
lens; because the lenses are converging, the lens with the longer focal
length creates a larger real image. (d) With the -15 D lens; because
the lenses are converging, the lens with the shorter focal length creates
a larger real image.
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