Study Notes on Absorption, Reflection, and Refraction

Absorption:
- Definition: Light hits an object and the energy is absorbed, warming the object without any light reflecting back.
Reflection:
- Definition: Light hits an object and bounces back at the same angle from which it came in (the angle of incidence equals the angle of reflection).

Light reflects off surfaces depending on the angle of incidence.
If the light hits at a steeper angle, it reflects at a corresponding steep angle.

During absorption, light energy is transformed into thermal energy, causing the object to warm up.
The light does not escape back from the object after it has been absorbed.

Definition: Refraction is the bending of light as it travels through different media with different densities (e.g., air to water, air to glass).
The direction of travel changes depending on the density difference between the two media.
The formula demonstrating refraction is given by Snell's Law: n1 \sin(\theta1) = n2 \sin(\theta2) where:
- $n1$ and $n2$ are the refractive indices of the two media,
- $\theta_1$ is the angle of incidence,
- $\theta_2$ is the angle of refraction.

If light hits at a 90-degree angle during refraction, it will not bend and will continue straight through.
The amount of bending is also influenced by the angle of incidence; a larger angle of incidence leads to a greater degree of bending and vice versa.

Observing a straw in a glass of water appears bent due to refraction is a common visual example.
Refraction is essential for the function of lenses, as they bend light to focus it at a single point on the retina, preventing a blurry image.
The lenses must adjust their shape to effectively focus light from objects at varying distances (near vs. far).

Focusing is critical to ensure that light rays converge at a single point on the retina.
If light rays from close objects diverge considerably, a rounded lens is necessary to converge them accurately.
Conversely, distant objects produce light rays that are nearly parallel, requiring a flatter lens to focus properly.

Problems such as nearsightedness (myopia) arise when the eyeball shape leads the light to converge before hitting the retina, causing blurry vision for distant objects.
Farsightedness (hyperopia) results when the light converges behind the retina if the eyeball is too short or if the lens is too flat.

Retina: The back of the eyeball containing photoreceptors that send signals to the brain.
Photoreceptors Types:
- Rods: Very sensitive to low light conditions, can detect very few photons (approximately one photon), but cannot perceive color, useful for night vision, and are located in the periphery of the retina.
- Cones: Responsible for color vision, need about 10-12 photons to activate. They come in three types responding to different wavelengths (colors):
- Blue cones: Best respond to blue light,
- Green cones: Best respond to green light,
- Red cones: Primarily respond to red/orange light.

Rods are densely packed in the peripheral regions of the retina, enabling low-light vision but poor color discrimination.
Cones are concentrated in the fovea (the center of the retina), allowing for detailed color vision and high acuity.

Photoreceptors send signals to bipolar cells, which then connect to ganglion cells. These ganglion cells' axons form the optic nerve (Cranial Nerve II), transmitting visual information to the brain.

Ganglion cells can have varying sizes of receptive fields:
- Larger receptive fields in the periphery result in less acuity, as multiple photoreceptors feed data to a single ganglion cell.
- Smaller receptive fields in the center improve visual detail and color discrimination.

The functioning of both rods and cones, along with the precise focusing of light through the lens and cornea, is essential for clear vision. Any disruption in this complex interaction can lead to visual impairments.