Mrs, Rashmi Singh brokeher readings glasses. When she went toshopkeeper to order new spects, he suggested that she shouldget spectacleswith plastic lensesinstead ofgalss lenses. On gettingthe new spectacles,she foundthat the new ones were thickerthan the earlierones.She askedthis questionto the shopkeeperbut he could not offer satisfactory explanation for this. At home, Mrs. Singh raised the same question to her daughter Anuja who explained whyplasticlenses were thicker. (a) Write two qualitiesdisplayedeach by Anuja and her mother . (b) How do youexplainthis fact using lens maker's formula ?

Mrs, Rashmi Singh brokeher readings glasses. When she went toshopkeepe

1.	Mrs, Rashmi Singh brokeher readings glasses. When she went toshopkeeper to order new spects, he suggested that she shouldget spectacleswith plastic lensesinstead ofgalss lenses. On gettingthe new spectacles,she foundthat the new ones were thickerthan the earlierones.She askedthis questionto the shopkeeperbut he could not offer satisfactory explanation for this. At home, Mrs. Singh raised the same question to her daughter Anuja who explained whyplasticlenses were thicker. (a) Write two qualitiesdisplayedeach by Anuja and her mother . (b) How do youexplainthis fact using lens maker's formula ?
Answer» Solution :(a) Anuja `rarr`Aware/ Explainer Mrs Rashimi `rarr` Curious/Observant (b) Lens maker FORMULA `1/f = (mu - 1) (1/(R_(1)) - 1/(R_(2))), mu_(g) gt mu_(p)` `g rarr "glass p" rarr "plastic"` So, `(mu_(g) - 1) gt (mu_(p) - 1)` From lens maker formula , focal length f is INVERSELY proportionalto `(mu - 1)`. So, `f_(p) gt f_(g)`thickness of plasticlens is to be increasedto keep focal length of the glass euqal.

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