Question 115: Ray Optics

Question

A photograph of a landscape is captured by a drone camera at a height of 18 km . The size of the camera film is $2 \mathrm{~cm} 	imes 2 \mathrm{~cm}$ and the area of the landscape photographed is $400 \mathrm{~km}^2$. The focal length of the lens in the drone camera is :

Accepted Answer

$$\begin{aligned}
&\mathrm{H}=18 \mathrm{~km}\
&	ext { Size of camera film }=2 \mathrm{~cm} 	imes 2 \mathrm{~cm}\
&\begin{aligned}
& \mathrm{A}_{	ext {image }}=400 \mathrm{~km}^2 \
& \mathrm{x}=20 	imes 10^3 \mathrm{~m}=2 	imes 10^4 \mathrm{~m} \
& \mathrm{y}=2 	imes 10^{-2} \mathrm{~m} \
& \frac{\mathrm{x}}{\mathrm{y}}=10^6=\frac{18 \mathrm{Km}}{\mathrm{f}} \
& \mathrm{f}=18 	imes 10^{-3} \mathrm{~m}=18 \mathrm{~mm} \
& \mathrm{f}=1.8 \mathrm{~cm}
\end{aligned}
\end{aligned}$$

Answer

2.8 cm

Answer

0.9 cm

Answer

2.5 cm

Answer

1.8 cm

Ray Optics

A photograph of a landscape is captured by a drone camera at a height of 18 km . The size of the camera film is 2 \mathrm{~cm} \times 2 \mathrm{~cm} and the area of the landscape photographed is 400 \mathrm{~km}^2. The focal length of the lens in the drone camera is :

Choose the correct answer: