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You have learnt in the text how Huygens' principle leads to the laws of reflection and refraction. Use the same principle to deduce directly that a point object placed in front of a plane mirror produces a virtual image whose distance from the mirror is equal to the object distance from the mirror. |
Answer» Solution : Consider a point object O in front of a plane mirror M, ABC is a spherical wavefront at an INSTANT of time, spread from O. had there been no mirror, this wavefront would occupy a position DEF in a time t. but points D and F on the mirror and every point lying betwen D and F acts as a source of secondary WAVELETS. these wavelets are REFLECTED back into the air. at the end of time t, DGF is the spherical wavefront which advances in air. this appears to come from I. thus, I is the VIRTUAL image of O. from Huyegen.s principle, if GB=h, then BE is ALSO equal to h. Fromm the theorem of intersection of chords `DB.BF=h(2r-h)=h(2R-h)`, where `r=OE and R=IG`. Therefore, r=R and IG=OE. Hence, we have IB=OB. Thus, the image is as far behind the mirror as the object is in front of it. |
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