An object is placed on the principal axis of a convex lens at a point between F 1 and 2 F 1 (F 1 is the principal focus to the left of the lens). The image formed is:
inverted and enlarged
Convex Lens Image Characteristics
Understanding how a convex lens forms images is crucial in optics. A convex lens, also known as a converging lens, bends parallel light rays towards a focal point.
Object Placement Between the Principal Focus and 2F1
The question asks us to determine the nature of the image formed when an object is placed on the principal axis of a convex lens at a point located between the first principal focus ($F_1$) and the point $2F_1$. The principal focus ($F_1$) is a key point on the axis related to how the lens refracts light.
Image Formation Analysis with Convex Lens
When an object is positioned between $F_1$ and $2F_1$ for a convex lens, the light rays interacting with the lens follow specific paths:
- A ray passing through the optical centre continues undeviated.
- A ray parallel to the principal axis refracts through the second principal focus ($F_2$).
- A ray directed towards $F_1$ refracts parallel to the principal axis.
These refracted rays converge at a point beyond $2F_2$ on the opposite side of the lens. This convergence point is where the image is formed. Based on the principles of ray tracing for a convex lens:
- Real Image: Since the light rays actually converge to form the image, it is a real image. Real images can be projected onto a screen.
- Inverted Image: The image formed is upside down relative to the orientation of the object.
- Enlarged Image: The size of the image is greater than the size of the object.
Evaluating the Options
Let's compare these derived characteristics with the given options:
- Option 1: erect and diminished - This is incorrect. Erect images formed by convex lenses are virtual, and diminished refers to a smaller image size.
- Option 2: inverted and enlarged - This accurately describes the image formed when the object is placed between $F_1$ and $2F_1$.
- Option 3: erect and enlarged - This is incorrect. An erect and enlarged image is formed when the object is placed between the optical centre and $F_1$.
- Option 4: inverted and diminished - This is incorrect. An inverted and diminished image is formed when the object is placed beyond $2F_1$.
Therefore, the correct description for the image formed when the object is placed between $F_1$ and $2F_1$ of a convex lens is that it is inverted and enlarged.
Important Questions from Refraction and Reflection
A convex lens of focal length f will form a magnified real image of an object, if the object is placed.
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