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Question Number 13054 by chux last updated on 12/May/17
An object is placed between a   converging lens and a plane mirror.  Explain how two real images of the  object may be produced by the   system.  If the focal length of the lens is 15cm  and the object is 20cm from both   the lens and the mirror.Calculate  the distance of the two images   from the lens..        pls help me with this....
$$\mathrm{An}\:\mathrm{object}\:\mathrm{is}\:\mathrm{placed}\:\mathrm{between}\:\mathrm{a}\: \\ $$$$\mathrm{converging}\:\mathrm{lens}\:\mathrm{and}\:\mathrm{a}\:\mathrm{plane}\:\mathrm{mirror}. \\ $$$$\mathrm{Explain}\:\mathrm{how}\:\mathrm{two}\:\mathrm{real}\:\mathrm{images}\:\mathrm{of}\:\mathrm{the} \\ $$$$\mathrm{object}\:\mathrm{may}\:\mathrm{be}\:\mathrm{produced}\:\mathrm{by}\:\mathrm{the}\: \\ $$$$\mathrm{system}. \\ $$$$\mathrm{If}\:\mathrm{the}\:\mathrm{focal}\:\mathrm{length}\:\mathrm{of}\:\mathrm{the}\:\mathrm{lens}\:\mathrm{is}\:\mathrm{15cm} \\ $$$$\mathrm{and}\:\mathrm{the}\:\mathrm{object}\:\mathrm{is}\:\mathrm{20cm}\:\mathrm{from}\:\mathrm{both}\: \\ $$$$\mathrm{the}\:\mathrm{lens}\:\mathrm{and}\:\mathrm{the}\:\mathrm{mirror}.\mathrm{Calculate} \\ $$$$\mathrm{the}\:\mathrm{distance}\:\mathrm{of}\:\mathrm{the}\:\mathrm{two}\:\mathrm{images}\: \\ $$$$\mathrm{from}\:\mathrm{the}\:\mathrm{lens}.. \\ $$$$ \\ $$$$ \\ $$$$ \\ $$$$\mathrm{pls}\:\mathrm{help}\:\mathrm{me}\:\mathrm{with}\:\mathrm{this}….\: \\ $$
Answered by ajfour last updated on 12/May/17
Commented by ajfour last updated on 12/May/17
(1/v)−(1/u)=(1/f)  (1/v)=(1/((−20)))+(1/(15))  = ((−15+20)/(300)) =(1/(60))  v=60cm  (1/(v′))−(1/(u′))=(1/f)  image of object in plane mirror  serves as the second object for  the lens.  its distance  u′=−60cm  (1/(v′))=(1/((−60)))+(1/(15))=((−1+4)/(60)) =(1/(20))  v′=20cm  distance between these two real  images  is v−v′=60cm−20cm                                   = 40cm .
$$\frac{\mathrm{1}}{{v}}−\frac{\mathrm{1}}{{u}}=\frac{\mathrm{1}}{{f}} \\ $$$$\frac{\mathrm{1}}{{v}}=\frac{\mathrm{1}}{\left(−\mathrm{20}\right)}+\frac{\mathrm{1}}{\mathrm{15}}\:\:=\:\frac{−\mathrm{15}+\mathrm{20}}{\mathrm{300}}\:=\frac{\mathrm{1}}{\mathrm{60}} \\ $$$${v}=\mathrm{60}{cm} \\ $$$$\frac{\mathrm{1}}{{v}'}−\frac{\mathrm{1}}{{u}'}=\frac{\mathrm{1}}{{f}} \\ $$$${image}\:{of}\:{object}\:{in}\:{plane}\:{mirror} \\ $$$${serves}\:{as}\:{the}\:{second}\:{object}\:{for} \\ $$$${the}\:{lens}. \\ $$$${its}\:{distance}\:\:{u}'=−\mathrm{60}{cm} \\ $$$$\frac{\mathrm{1}}{{v}'}=\frac{\mathrm{1}}{\left(−\mathrm{60}\right)}+\frac{\mathrm{1}}{\mathrm{15}}=\frac{−\mathrm{1}+\mathrm{4}}{\mathrm{60}}\:=\frac{\mathrm{1}}{\mathrm{20}} \\ $$$${v}'=\mathrm{20}{cm} \\ $$$${distance}\:{between}\:{these}\:{two}\:{real} \\ $$$${images}\:\:{is}\:{v}−{v}'=\mathrm{60}{cm}−\mathrm{20}{cm} \\ $$$$\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:=\:\mathrm{40}{cm}\:. \\ $$
Commented by chux last updated on 12/May/17
wow...... this is wonderful...I   really appreciate.
$$\mathrm{wow}……\:\mathrm{this}\:\mathrm{is}\:\mathrm{wonderful}…\mathrm{I}\: \\ $$$$\mathrm{really}\:\mathrm{appreciate}. \\ $$

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