Question

One dioptre is the power of a lens whose focal length is:

Options

• 1 metre

• 10 metres

• 1 centimetre

• 1 millimetre

Answer 1

By definition, one dioptre is the power of a lens whose focal length is 1 metre. Using \[P = \frac{1}{f(m)}\], a focal length of 1 m gives \[P = 1\,D\].