Light and Quantized Energy

1. Light and Quantized Energy Chapter 5 Section 1

2. Wave Nature of Light • Electromagnetic radiation is a form of energy that exhibits wavelike behavior as it travels through space. • Ex:

3. Parts of a wave • Wavelength is the shortest distance between equivalent points on a continuous wave. • Represented by λ • Usually expressed in meters, centimeters of nanometers

4. Parts of a wave • Frequency is the number of waves that pass a given point per second. • Represented by v • Usually expressed in Hertz which equals one wave per second

5. Parts of a wave • The amplitude of a wave is the wave’s height from the origin to a crest, or from the origin to a trough. Crest Trough

6. All electromagnetic waves travel at the speed of light which is 3.00 x 108 m/s in a vacuum. • The speed of light is given its own symbol, c. • Wavelength times frequency equals the speed of light. • c = λ v

7. Wavelength and frequency are inversely related so as one increases, the other decreases.

8. Sunlight passing through a prism is separated into a continuous spectrum of colors. • The visible spectrum of light comprises only a small portion of the complete electromagnetic spectrum.

9. Electromagnetic Spectrum

10. The electromagnetic spectrum, also called the EM spectrum, encompasses all forms of electromagnetic radiation, with the only differences being their wavelength and frequencies. • Short wavelengths bend more than long wavelengths in a prism. • R O Y G. B I V Shortest Wavelength el low ed range reen ndigo iolet lue

11. Particle Nature of Light • In 1900, the German physicist Max Planck concluded that: matter can gain or lose energy only in small, specific amounts called quanta. • A quantum is the minimum amount of energy that can be gained or lost by an atom.

12. The Quantum Concept • Planck came up with an equation that showed the energy of a quantum is related to the frequency of the emitted radiation: • Equantum=hv • Planck’s constant has a value of 6.626 x 10-34 Js (J = joules) Matter can only absorb energy in whole-number multiples of hv. E = energy h = Planck’s constant v = frequency

13. The Photoelectric Effect • In the photoelectric effect, electrons called photoelectrons, are emitted from a metal’s surface when light of a certain frequency shines on the surface. • Albert Einstein proposed in 1905 that light has many wavelike characteristics, but it can also be though of as a stream of tiny particles, or bundles of energy, called photons.

14. The Photoelectric Effect • A photon is a particle of electromagnetic radiation with no mass that carries a quantum of energy. • Einstein calculated that a photon’s energy depends on its frequency: • Ephoton= hv

15. Atomic Emission Spectra • The atomic emission spectrum of an element is the set of frequencies of the electromagnetic waves emitted by atoms of the element. • It is not a continuous range of colors but rather individual lines of color. • All elements have unique atomic emission spectra.

16. Atomic Emission Spectra • Flame tests can be used to identify whether certain elements are present in compounds. Only these bands of colors are seen with a spectroscope.