The lady uses glasses of +1.5 D to have a normal vision from 25 cm onwards.
Least distance of clear vision,D=25cm
Focal length of the glasses, f=1 power=11.5 m
She should have the greater least distance of distinct vision without the glasses.
Take:
u=−25 cm=−0.25 m
The lens formula is given by
1v+1u=1f
Putting the values, we get:
v=0.4m=40cm
Near point without glasses =40cm
The focal length of the magnifying glass,f=0.05 m=5 cm
(a) The maximum magnifying power if she uses the microscope together with her glass is given by
m=1+Df
Here,
D=25cm
f=5cm
On substituting the values, we get:
m=6
(b) Without the glasses, D=40cm.
∴ m=1+Df=1+405=9