An object AB of height 1cm lying on the axis of convex mirror of focal length20cm, at a distance of 30cm from its pole as shown in figure. Now the object starts moving with a constant speed `1 cm//sec` towards the pole. Calculate Q. Rate of change of height of image.A. `0.16cms^(-1)`B. `0.004cms^(-1)`C. `0.016cms^(-1)`D. `0.0008cms^(-1)`

An object AB of height 1cm lying on the axis of convex mirror of focal

1.	An object AB of height 1cm lying on the axis of convex mirror of focal length20cm, at a distance of 30cm from its pole as shown in figure. Now the object starts moving with a constant speed `1 cm//sec` towards the pole. Calculate Q. Rate of change of height of image.A. `0.16cms^(-1)`B. `0.004cms^(-1)`C. `0.016cms^(-1)`D. `0.0008cms^(-1)`
Answer» Correct Answer - d. (i) Given : `u=-30cm, f=20cm` `(1)/(v)+(1)/(u)=(1)/(f)rArrv=12cm` Also, `(dv)/(dt)=-((v^(2))/(u^(2)))(du)/(dt)=-0.16cms^(-1)` (ii) `H=-(v)/(u)h`, H is the height of image and h is height of object. `(dH)/(dt)=(u(dv)/(dt)-v(du)/(dt))/(u^(2))h=0.008cms^(-1)`

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