Скачать или смотреть A photograph of a landscape is captured by a drone camera at a height of 18 km. The size of the came

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 cm × 2 cm and the area of the landscape photographed is 400 km² . The focal length of the lens in the drone camera is :
(1) 1.8 cm (2) 2.8 cm
(3) 2.5 cm (4) 0.9 cm

✅ Understanding Focal Length of Camera Lens in Drone Photography | JEE Mains 2025 💯🔥
📸 Introduction to Focal Length in Optics | Drone Camera Problem 💯🚀
In optics, understanding the concept of focal length is essential, especially when dealing with camera lenses, telescopes, microscopes, and other optical instruments. The given question, asked in JEE Mains 2025, involves calculating the focal length of the lens of a drone camera that captures a photograph of a landscape from a height of 18 km.

This question falls under the concept of optics and ray optics, which is a very important chapter for both JEE Mains 2025 and NEET 2025. Candidates must have a strong understanding of:
✅ Focal length of a camera lens.
✅ Magnification in optical systems.
✅ Image formation by convex lenses.
✅ Application of lens formula in practical problems.
✅ Real-life applications of drone photography using lenses.

In this detailed explanation, we will break down everything conceptually to understand:

What is the focal length of a camera lens?
How does a drone camera capture large landscape images from high altitude?
What is the relation between object distance, image distance, and focal length?
Why is this concept important for JEE Mains 2025 and NEET 2025?
✅ What Is a Camera Lens and How Does It Work? 📸🔍
A camera lens is a converging optical lens that captures light from an object (landscape, person, building, etc.) and forms a reduced image on the camera sensor or film.

The working of a camera lens is based on the principle of:
✅ Refraction of light.
✅ Convergence of light rays at the focal point.
✅ Formation of a reduced image on the film/sensor.

In simple terms, when a drone camera captures an image from a height, the light from the landscape enters the camera lens, converges, and forms a small image on the camera film or sensor. The distance from the lens to the sensor where the image is formed is called the focal length of the camera.

✅ What Is Focal Length of a Lens in Camera? 📏📸
The focal length of a lens in a camera refers to the distance between the lens and the image sensor/film when the lens is focused at infinity.

In a camera lens, the focal length controls the magnification and field of view of the captured image.
A longer focal length results in a more zoomed-in image.
A shorter focal length results in a wider field of view, capturing a large area in a single shot.
Mathematically, the focal length is defined using the lens formula, which relates:
✅ Object distance (distance of landscape from the camera).
✅ Image distance (distance from lens to the film).
✅ Focal length of the lens.

✅ How Does a Drone Camera Capture a Large Landscape from High Altitude? 🚁📸
In the given question, the drone camera is flying at a height of:
✅ 18 km from the ground.
✅ It captures a landscape area of 400 km².
✅ The camera film size is 2 cm × 2 cm.

Since the camera is at a significant height (18 km), the image formed on the camera film is highly reduced compared to the actual size of the landscape. This is where the concept of focal length and image formation becomes crucial.

✅ Why Is the Image Size So Small on the Film? 💯🔥
The image formed on the camera film is very small because:

The camera lens converges light rays from the large landscape.
Since the distance between the camera and landscape is very large (18 km), the image formed on the film is highly reduced.
The size of the image is proportional to the focal length of the lens.
In practical drone photography:

Higher altitudes produce smaller images on the film.
Smaller focal length lenses are used for capturing wide-area images.
Larger focal length lenses are used for zoomed-in images (like telescopes).
✅ Relation Between Object Distance, Image Distance, and Focal Length 💯📸
In any camera lens system, the relationship between:

Object distance (distance of landscape from camera).
Image distance (distance from lens to film).
Focal length of the lens.
is governed by the lens formula. This formula helps determine the focal length when the:
✅ Height of drone = 18 km.
✅ Area of landscape = 400 km².
✅ Image size on film = 2 cm × 2 cm.

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