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Question Id:  PH0000004 Question :  What is the Newton's formula for spherical mirror? Solution :   A useful formula for spherical mirror is Newton's formula Here "O" is the object and "I" is the image of the object. Let the distance of the object from the pole is \(u\) and distance of the object from the pole is \(v\) .  Let the distance of the object and the image from the principal focus be \(x\) and \(y\) respectively. So, \(x=u-f\Rightarrow u=f+x\) And \(y=v-f\Rightarrow v=f+y\) Using the value of \(u\) and \(v\) in the formula of mirror gives \[\frac{1}{u}+\frac{1}{v}=\frac{1}{f}\] \[\Rightarrow \frac{1}{f+x}+\frac{1}{f+y}=\frac{1}{f}\] \[\Rightarrow \frac{f+y+f+x}{(f+x)(f+y)}=\frac{1}{f}\] \[\Rightarrow \frac{2f+y+x}{(f+x)(f+y)}=\frac{1}{f}\] \[\Rightarrow 2f^{2}+fy+fx=f^{2}+fx+fy+xy\] \[\Rightarrow 2f^{2}=f^{2}+xy\] \[\Rightarrow f^{2}=xy\] The above equation is the Newton's formula for Spherical mirror. As \(f\) is constant [ i.e \(f=\frac{r}{2}...

Question Id: PH0000002 Question :   Find radius of the curvature of the concave mirror having focal length 7.5 cm. To find : radius (r) of the curvature Solution :   we know the relation between focal length (f) and radius (r)  of curvature of mirror is \[\Rightarrow f=\frac{r}{2}\] \[\Rightarrow r=2 \times f\] \[\Rightarrow r=2 \times 7.5\] \[\Rightarrow r=15\] ∴ Hence radius of the curvature of the concave mirror is \(15cm\) . (Answer)   If you have any problem regarding this please leave a comment 💬 below