Question

Power of a lens is $-2D$. What type of lens is this? Find the focal length of the lens.

Answer 1

Step 1: Given data,

The power of the lens is $-2D$.

Step 2: Finding the type of lens,

As the power of the lens is negative, the provided lens is concave.

Thus, the type of lens is concave.

Step 3: Finding the focal length of the lens,

According to the power of lens formula,

$Poweroflens=\frac{1}{focallengthofthelens}$

Substituting the known values,

$$\begin{gathered} -2D=\frac{1}{focallengthofthelens} \\ -2=\frac{1}{focallengthofthelens} \\ focallengthofthelens=-\frac{1}{2} \\ focallengthofthelens=-0.5\text{m} \end{gathered}$$

Here, the negative sign indicates that the lens is concave.

Thus, the focal length of the lens is $0.5m$.