The human eye is like a camera that has a lens with:
- A.fixed focal length and fixed aperture size.
- B.variable focal length and fixed aperture size.
- C.fixed focal length and variable aperture size.
- D.variable focal length and variable aperture size.
Correct answer
Explanation
The correct answer is D, variable focal length and variable aperture size. The eye changes the focal length of its lens to focus and changes the size of its pupil to control the light.
The eye lens is soft and is held by ciliary muscles. To see a distant object these muscles relax and the lens becomes thin, increasing its focal length; for a near object they contract, the lens becomes thicker and its focal length decreases. This power of adjustment is called accommodation. At the same time the iris acts like a camera's diaphragm: in bright light it makes the pupil small, and in dim light it widens the pupil to let in more light.
A is wrong: neither the focal length nor the opening of the eye is fixed.
B is wrong: the pupil, which is the eye's aperture, does change size with the light.
C is wrong: the focal length must change, or we could not focus on both near and far objects.
Exam tip: ciliary muscles change the focal length (accommodation); the iris changes the pupil, the eye's aperture.
Practice Questions
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- B.diploid zygote
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- D.motile male gametes
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- A.One
- B.Two
- C.Three
- D.Four
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- A.10⁻⁷ cm
- B.10⁻⁶ cm
- C.10⁻⁴ cm
- D.10⁻³ cm
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- A.CₙH₂ₙ₊₂
- B.CₙH₂ₙ₋₂
- C.CₙH₂ₙ₊₁
- D.CₙH₂ₙ₋₁
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- A.Cholera
- B.Malaria
- C.Smallpox
- D.Elephantiasis
Show answer
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