With respect to electromagnetic waves, the human eye is sensitive to
- A.both electric and magnetic fields
- B.electric field only
- C.magnetic field only
- D.infrared part of the electromagnetic spectrum
Correct answer
Explanation
The correct answer is B, electric field only. Vision is caused by the electric field of light acting on the light-sensitive molecules of the retina.
Light is an electromagnetic wave in which electric and magnetic fields oscillate at right angles to each other and to the direction of travel. The force a wave exerts on a charge through its magnetic field is smaller than that of its electric field by a factor of v/c, and the electrons in a molecule move far slower than light, so this magnetic effect is negligible. It is the electric field that excites the retinal pigment in rods and cones. For this reason the electric field vector is called the light vector, and the plane of polarisation is described by it.
A is wrong because the magnetic field's effect on the eye's molecules is negligible.
C is wrong for the same reason: the magnetic field alone does not produce vision.
D is wrong because the eye sees roughly 400–700 nm, the visible band; infrared is felt as heat, not seen.
Exam tip: the electric vector of light is the 'light vector' responsible for vision and photographic effects.
Practice Questions
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- A.Hg
- B.Si
- C.Ti
- D.Sn
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- A.Scales
- B.Root hairs
- C.Endodermis
- D.Stomata
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Read the full explanation →Bending of shoot of a plant towards light can be referred to as
- A.photonasty
- B.positive phototropism
- C.negative phototropism
- D.photoperiodism
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Read the full explanation →Which of the following organisms belongs to Coelenterata (Cnidaria)?
- A.Planaria and liverfluke
- B.Sea urchin and sea cucumber
- C.Hydra and sea anemone
- D.Euplectella and sycon
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- A.anti-malarial drug
- B.biodiesel
- C.pulp for paper industry
- D.textile fibre
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