Chapter 8 - Light Notes

Waves

• Definition: A wave is a disturbance or oscillation that transfers energy through space and matter.

• Wave Characteristics:

  • Amplitude (y): The measure of the wave's displacement or density.

  • Wavelength (λ): The size of the wave, measured in meters or nanometers.

  • Velocity Calculation: The velocity of a wave can be found by timing how long it takes for one wavelength to pass a point.

Light

• Nature of Light: Light is an electromagnetic wave with a constant velocity of c = 3.0 x 10^8 m/s (approximately 186,282 mi/s).

• Wavelength and Frequency:

  • Relationship: Wavelength (λ) is inversely proportional to frequency (f): c = λf.

  • Speed is also inversely proportional to frequency

Visible Light

• Human Eye Sensitivity:

  • Humans perceive different frequencies of light as color; these frequencies correspond to different energy levels.

• Energy Calculation: Light energy can be calculated using:

  • E = hf or E = hc/λ where h = 6.626 x 10^-34 Js.

  • For example, red light (700 nm) has an energy of approximately 2.83 x 10^-19 J or 1.77 eV.

Color and the Human Eye

• Cones and Rods:

  • The human eye uses three types of photoreceptors called cones (red, green, blue) to see colors and rods for brightness.

Color Blindness

• Statistics:

  • Affects 5% of men and 0.5% of women.

  • Result of missing certain cones, leading to difficulties in perceiving parts of the visible spectrum:

  • Protanopia: Red-green weak.

  • Tritanopia: Blue-yellow weak.

  • Monochromacy: Complete color blindness.

Images and Vision

• Light Rays and Images: When light passes through a small opening, the resulting image is inverted.

• Anatomy of the Eye:

  • Cornea, Pupil, Lens, Retina: Key components that focus light.

• Common Vision Issues:

  • Myopia (Nearsightedness): Image focused in front of the retina.

  • Hyperopia (Farsightedness): Image focused behind the retina.

Mirrors and Reflection

• Light Behavior: Light travels in straight lines and can produce virtual images through reflection.

Retro-Reflectors

• Functionality: Devices that bounce light back in the same direction it came from, used in moon missions to measure the speed of light.

Index of Refraction

• Definition: The index of refraction (n) measures how much slower light travels in mediums compared to a vacuum: n = c / vm.

Bending of Light

• Snell’s Law: Describes how light bends when passing through different materials with varying indices of refraction.

• Ex: If light is passed through air to water, It bends towards the normal due to the higher index of refraction of water, resulting in a change in its speed and direction.

• Mirages: Optical illusions caused by refraction of light through layers of differently heated air.

Total Internal Reflection

• Conditions: Occurs when the angle of incidence exceeds the critical angle, resulting in light reflecting back rather than refracting.

• Critical Angles for common materials (e.g., air to water, air to glass) are crucial for optical applications.

• Applications: Utilized in fiber optics and explaining rainbows.

Polarization of Light

• Definition: Nonpolarized light vibrates in all directions, while polarized light vibrates in a single direction.

• Applications: Used in polarizers and liquid crystal displays (LCDs).

3D Images and Binocular Vision

• Vision: Binocular vision provides depth perception and three-dimensional awareness through the coordination of both eyes.

• 3D Movies: Achieved through specialized viewing glasses.

Diffraction of Light

• Phenomenon: Light can diffract and interfere, creating patterns like those seen in single-slit and double-slit experiments.

Spectral Lines and Emission Spectra of Elements

• Emission Spectra: Unique spectral lines for elements such as Hydrogen and Helium can be used to identify them and understand energy transitions in atoms.