(II) A certain lens focuses light from an object 1.55 m away...

Name: Problem 44, Chapter 23: Physics: Principles with Applications
Uploaded: 2019-05-10T01:13:05-08:00
Duration: 1 min 23 s
Channel: Kyle Godbey
Description: (II) A certain lens focuses light from an object 1.55 m away as an image 48.3 cm on the other side of the lens. What type of lens is it and what is its focal length? Is the image real or virtual?

(II) A certain lens focuses light from an object 1.55 m away as an image 48.3 cm on the other side of the lens. What type of lens is it and what is its focal length? Is the image real or virtual?

Key Concepts

Types of Lenses (Convex vs Concave)

Lenses are typically classified as convex or concave based on their shape and optical behavior. A convex lens converges parallel rays of light to a point (focal point) and is used to produce real images when the object is placed outside the focal point. In contrast, a concave lens diverges light rays and produces virtual images. The type of lens used thus determines the nature of image formation.

Real vs Virtual Images

Real images are formed when light rays converge at a point and can be projected onto a screen, whereas virtual images result from rays that appear to diverge from a point behind the lens. The distinction is important because it determines the properties of the lens needed to form the image and how the image will be perceived or recorded.

Thin Lens Equation

The thin lens equation relates the focal length (f) of a lens to the object distance (d?) and the image distance (d?) through the formula 1/f = 1/d? + 1/d?. This equation is fundamental in geometrical optics and is used to determine any one of these values when the other two are known.

Sign Conventions

Sign conventions in optics are important for correctly applying the thin lens equation. They dictate whether distances are considered positive or negative based on the orientation of the object and image relative to the lens. Typically, object distances are positive, and the image distance is assigned a positive sign if the image is real (formed on the opposite side of the lens to the object) and a negative sign if the image is virtual.

Focal Length

The focal length of a lens is the distance from the lens at which parallel rays of light either converge or appear to diverge. It is a key parameter that determines the imaging properties of the lens. The focal length is computed using the thin lens equation once the distances of the object and image are known.

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