.png "NOTES Class 10 Science chapter 9: Light – Reflection and Refraction - 3")
Image Formation by Lenses
Lenses form images by refracting light. The nature of these images depends on whether the lens is convex or concave.
Convex Lens
A convex lens converges light rays passing through it. Here’s a step-by-step process of how images are formed using a convex lens:
At Infinity
When the object is placed at infinity, rays parallel to the principal axis converge at the principal focus . The image formed is highly diminished, point-sized, real, and inverted.
Beyond 2F1
When the object is placed beyond twice the focal length , the image forms between and , which is diminished, real, and inverted.
At 2F1
Placing the object at creates an image at with the same size as the object, real, and inverted.
Between F1 and 2F1
The image forms beyond , magnified, real, and inverted.
At F1
The image forms at infinity, highly magnified, real, and inverted.
Between F1 and O
The image forms on the same side as the object, magnified, virtual, and erect.
Concave Lens
A concave lens diverges light rays, making them appear to emanate from the principal focus . The image formation is simpler:
At Infinity
When the object is at infinity, the image forms at the focus , highly diminished, point-sized, virtual, and erect.
Between Infinity and Optical Center
When the object is placed between infinity and the optical center , the image forms between the focus and the optical center, diminished, virtual, and erect.
Sign Convention for Spherical Lenses
The sign convention for lenses is similar to that for spherical mirrors. Distances are measured from the optical center of the lens:
- Distances measured in the direction of the incident light are positive.
- Distances against the direction of the incident light are negative.
- The focal length of a convex lens is positive, and that of a concave lens is negative.
Lens Formula and Magnification
The lens formula establishes a relationship between the object distance , image distance , and focal length :
Magnification is the ratio of the height of the image to the height of the object .
Power of a Lens
The power of a lens is defined as the reciprocal of its focal length (in meters):
The unit of power is the diopter (D).
Ray Diagrams
Ray diagrams help understand the path taken by light rays through lenses.
Convex Lens
Key rays include:
- A ray parallel to the principal axis passing through the principal focus.
- A ray passing through the optical center without deviation.
- A ray passing through the focus emerging parallel to the principal axis.
Concave Lens
Key rays include:
- A ray parallel to the principal axis appearing to diverge from the principal focus.
- A ray appearing to pass through the optical center without deviation.
- A ray directed towards the principal focus emerging parallel to the principal axis.
Examples
Concave Lens Example
Convex Lens Example
Applications of Lenses
Convex Lenses
Used in magnifying glasses, cameras, projectors, and eyeglasses for hyperopia (farsightedness).
Concave Lenses
Used in eyeglasses for myopia (nearsightedness) and various scientific instruments.
These principles and formulas form the foundation for understanding how lenses manipulate light, crucial for various optical devices and practical applications.
Mind Map for Light – Reflection and Refraction
Image Formation by Lenses
Convex Lens
- At Infinity: Image at , real, inverted
- Beyond : Image between and
- At : Image at , same size
- Between and : Image beyond , magnified
- At : Image at infinity, highly magnified
- Between and O: Image on same side, virtual, magnified
Concave Lens
- At Infinity: Image at , virtual, point-sized
- Between Infinity and O: Image between and O, virtual, diminished
Sign Convention
- Distances from optical center
- Positive direction: with incident light
- Negative direction: against incident light
- Convex lens focal length: positive
- Concave lens focal length: negative
Lens Formula
- Magnification:
Power of Lens
(Diopters)
Ray Diagrams
Convex Lens
- Parallel to principal axis: through focus
- Through optical center: no deviation
- Through focus: parallel to principal axis
Concave Lens
- Parallel to principal axis: appears from focus
- Through optical center: no deviation
- Towards focus: parallel to principal axis
Applications
Convex Lenses
- Magnifiers, cameras, projectors, hyperopia correction
Concave Lenses
- Myopia correction, scientific instruments
.png&description=NOTES Class 10 Science chapter 9: Light – Reflection and Refraction - 3){kind=link}
0 Comments