lecture recording on 13 March 2025 at 12.14.36 PM

Speed of Light

• Speed of flight: ( 3.00 \times 10^8 ) m/s (also noted as ( 2.998 \times 10^8 ) m/s)

• Unit: meter per second (m/s)

Wavelength and Units

• Commonly measured in nanometers (nm).

• Difference between nanometer and meter:

  • 1 nanometer = ( 10^{-9} ) meters

  • Conversion is key for calculations in this chapter.

• Wavelength refers to visible light (red, blue, green) within the electromagnetic spectrum which is usually measured in nanometers.

Understanding Nanometers

• Definition: A nanometer is smaller than a meter, specifically one billionth of a meter.

• 1 m = ( 10^9 ) nm.

• The term "nano" represents ( 10^{-9}

Electromagnetic Radiation

• Light exhibits both wavy and particle properties (wave-particle duality).

• Light behaves as both a wave and has associated energy.

• Key Properties of Waves:

  • Wavelength (( \lambda )):

    • Measured in meters or nanometers.

    • Defined as the distance between two consecutive peaks in a wave.

  • Frequency (( BC ) or ( f )):

    • The number of wavelengths that pass a given point in a unit of time, measured in Hertz (Hz).

    • ( 1 \text{ Hz} = 1 ext{ wave per second} ).

Relationship between Wavelength, Frequency, and Speed of Light

• Equation: ( c = \lambda \cdot BC )

  • Where:

    • ( c ) = speed of light (approximately ( 2.998 \times 10^8 ) m/s)

    • ( \lambda ) = wavelength

    • ( BC ) = frequency

• Inverse relationship:

  • Increasing wavelength results in decreasing frequency and vice versa.

• Discuss observing electromagnetic spectrum trends.

Energy of Light

• Energy can be calculated using: ( E = h \cdot BC )

  • ( E ) = energy of a photon

  • ( h ) = Planck's constant (approximately ( 6.626 \times 10^{-34} ) joule seconds)

  • ( BC ) = frequency of light

• Relationship between energy and wavelength:

  • Derived equation using ( E ) and ( \lambda ): ( E = rac{h imes c}{\lambda} )

  • The equation can be used for calculations of energy based on given wavelengths.

Example Problem

• Given a wavelength of 640 nm, find energy of one photon emitted from neon atoms:

  1. Convert 640 nm to meters: ( 640 \text{ nm} = 640 \times 10^{-9} \text{ m} )

  2. Use ( E = \frac{h imes c}{\lambda} ) with ( h ) and ( c ) values.

  3. Expected result: energy of photon around ( 3.11 \times 10^{-19} ) joules, considered a very small amount of energy.