05_lecture

Chapter 5: Light and Matter

How Do We Experience Light?

• Light is a form of energy, felt as warmth from sunlight.

• Measured in watts: 1 watt = 1 joule/second.

Colors of Light

• White light consists of all colors of the rainbow.

Interactions of Light with Matter

• Emission: Process of light being produced.

• Absorption: Matter absorbing light.

• Transmission: Transparency of objects to light.

  • Transparent objects transmit light.

  • Opaque objects block light.

• Reflection/Scattering:

  • Mirrors reflect light directionally.

  • Movie screens scatter light.

What is Light?

• Light behaves as both a wave and a particle (photons).

Waves

• Waves carry energy without transporting matter.

• Wavelength: Distance between wave peaks.

• Frequency: Number of wave vibrations per second.

• Wave Speed Formula: Wave speed = wavelength × frequency.

Electromagnetic Waves

• Light waves are vibrations of electric and magnetic fields.

• Interaction with charged particles is influenced by these fields.

Wavelength, Frequency, and Energy

• Relations: wavelength × frequency = speed of light (constant).

• Photon energy: E = h × f (where h = Planck's constant).

Polarized Sunglasses

• Polarization indicates the vibration direction of light waves.

• Polarized lenses block reflected light off horizontal surfaces.

The Electromagnetic Spectrum

• Ranges from gamma rays to radio waves, characterized by different wavelengths and frequencies.

• Structure aligns different electromagnetic sources from cosmic phenomena to everyday machines.

Types of Spectra

• Continuous Spectrum: Light from sources like light bulbs emits all visible wavelengths.

• Emission Line Spectrum: Thin gas emits light at specific wavelengths.

• Absorption Line Spectrum: Cloud of gas absorbs specific wavelengths of light, resulting in dark lines.

Chemical Fingerprints

• Unique transition patterns in atoms produce specific emission or absorption lines.

• These lines help identify atomic presence in objects.

Energy Levels of Molecules

• Molecules have energy levels due to vibrations and rotations, leading to complex spectra, mainly in infrared.

Thermal Radiation

• All dense objects emit thermal radiation related to their temperature.

• Hotter objects emit more light and higher energy photons.

Doppler Shift

• Indicates the motion of distant objects based on light wavelength changes:

  • Blueshift: When objects approach.

  • Redshift: When objects recede.

• Measures speed through shifts in spectral line wavelengths.