Converging and Diverging Lenses

• A lens is a shaped, transparent object that refracts light to form an image.

Basic Lens Shapes

• Converging Lens: Thickest in the middle, thinnest at the edge.
• Diverging Lens: Thinnest in the middle, thickest at the edge.

Converging Lens

• Refracts parallel incident rays to converge at a single point on the opposite side.
• Has focal points on both sides for ray diagrams.
• Principal Focus (F): Located on the opposite side of the lens from incident rays, where rays converge.
• Secondary Principal Focus (F’): Located on the same side as the incident rays.
• Optical Centre (O): The exact center of the lens.

Diverging Lens

• Refracts parallel incident rays to diverge on the opposite side of the lens.
• The brain projects these rays backward, appearing to originate from a focal point in front of the lens.
• Principal Focus (F): Located on the same side as the incident rays, where rays appear to converge.
• Secondary Principal Focus (F’): Located on the opposite side as the incident rays.

Images in a Converging Lens

• Object beyond 2F: The image is larger, inverted, and real (as opposed to virtual).
• Object at the secondary focus: No clear image forms.
• Object inside the secondary focus: The image is larger, located in front of the lens (between 2F1 & F1), upright, and virtual.

Rules for Locating the Image in a Diverging Lens

• A ray parallel to the principal axis refracts as if it came through the principal focus.
• A ray appearing to pass through the secondary focus (F’) refracts parallel to the principal axis.
• A ray through the optical center (O) continues straight without refraction.

Images in a Diverging Lens

• A diverging lens always forms a smaller, upright, virtual image on the same side (between O & F) as the object.

Lens Rules for Ray Diagrams

• Draw any two of the following rays: one parallel to the principal axis refracting towards the principal focus (F); one through the optical center (O); or one towards the secondary focus (F’) refracting parallel to the principal axis.
• For converging lenses, the principal focus is on the opposite side of the object. For diverging lenses, it's on the same side.

Converging Mirror

• A convex lens where actual light rays converge on the opposite side of the mirror.
• Object beyond F’ forms an inverted, real image.
• Object close to the lens forms an upright, virtual image.

Diverging Mirror

• A concave lens where actual light rays diverge, but virtual rays meet on the same side of the mirror.
• The image is always upright and virtual.

Imperfect Accommodation

• Hereditary or age-related factors can lead to Myopia (nearsightedness) or Hyperopia (farsightedness).
• Myopia: Near objects are clear, far objects are unclear. Corrected with a diverging (concave) lens. The image falls short of the retina.
• Hyperopia: Far objects are clear, near objects are unclear. Corrected with a converging (convex) lens, light converges before hitting the natural lens of the eye. The image forms beyond the retina.

Applications

• Laser Eye Surgery: Reshapes the cornea to correct misshapen eyes, reducing the need for corrective lenses.
• Cataracts Eye Disease: The lens becomes cloudy, causing blurry vision, often with age. Surgery can replace the cloudy lens.

Blind Spot

• The area where the retina connects to the optic nerve, lacking rods and cones.
• The optic nerve transmits information to the occipital lobe.

Color Blindness

• Occurs when one or more cones are defective.
• Red-green color blindness is the most common, caused by a genetic defect on the X chromosome.