Chapter 23, Problem 44P

To determine

(a)

Type of lens.

Answer to Problem 44P

Solution:

Converging lens, positive power.

Explanation of Solution

Given:

Sunlight is observed to focus at a point $16.5\text{cm}$ behind the lens. I.e. Focal length, $f=16.5\text{cm}$

Formula used:

Power in dioptre $=\frac{1000}{f}$

Where, $f$ is focal length in $\text{mm}$.

Calculation:

Type of lens is converging lens with positive power.

To determine

(b)

Power of lens in dioptres.

Answer to Problem 44P

Solution:

Power in dioptres $=6.06$

Explanation of Solution

Given:

Sunlight is observed to focus at a point $16.5\text{cm}$ behind the lens. I.e. Focal length, $f=16.5\text{cm}$

Formula used:

Power in dioptre $=\frac{1000}{f}$

Where, $f$ is focal length in $\text{mm}$.

Calculation:

Power in dioptre is given by the formula $\frac{1000}{f}$. Where $f$ is focal length of the lens in $mm$. Here $f=16.5\text{cm}=165\text{mm}$

$\begin{array}{l}=\frac{1000}{16.5\times 10}\\ =\frac{1000}{165}\\ =6.06\end{array}$