Which of the following lenses will have the greatest power?

Power of the lens, P = $\frac{1}{\mathrm{Focal} \mathrm{length} \left(\mathrm{f}\right)}$

When the focal length= -2 m, ${\mathrm{P}}_1=\frac{1}{-2}= -0.5\mathrm{D}$

When the focal length= -3 m, ${\mathrm{P}}_2=\frac{1}{3}= 0.33\mathrm{D}$

When the focal length= -10 m, ${\mathrm{P}}_3=\frac{1}{-10}= -0.1\mathrm{D}$

When the focal length= 5 m, ${\mathrm{P}}_4=\frac{1}{5}= 0.2\mathrm{D}$

• We can see that the highest magnitude power of the lens is -0.5D.
• We only examine the magnitude of a lens' power when comparing its power to other lenses' powers because the sign only indicates whether the lens is concave or convex.

Therefore the lens with a focal length of -2m will have the highest power which means it will bend the light rays to the maximum extent.