2. Dual nature of light. EM spectrum.

Question 1

What does dual nature of light mean?

Answer 1

dual = wave & particle at the same time

Question 2

What are reasons for the wave character of light?

Answer 2

reasons for wave character stated by Huygen:

• diffraction
• interference
• polarization

Question 3

What are reasons for the particle character of light?

Answer 3

reasons for particle character stated by Newton:

• photoelectric effect
• refraction
• excitation, ionization
• Compton scatter
• pair production

Question 4

Define electromagnetic spectrum.

In which ranges can esp. particle or wave character be observed?

Answer 4

EM radiation intensities as a function of energy lined up according to their frequencies

• long wavelengths = wave
• short wavelengths = particle

_{(remember velocity-wavelength-frequency relation)}

Question 5

What is a electromagnetic wave?

What are its properties related in a formula?

Answer 5

EM disturbance propogating through space

• no elastic medium required
• both electric and magnetic field components, which oscillate in phase perpendicular to each other and perpendicular to the direction of energy propagation

properties: c = λ * f

• c = velocity
• λ = wavelength
• f = frequency

Question 6

How was the wave character of light proven?

Question 7

Which principle is related to that experiment?

Answer 7

Huygens-Fresnel principle:

as radiation passes through a slit smaller than its wavelength, the slit behaves like a radiation source, and “emits” the radiation in every direction
⇒ diffraction

→ every point of a wavefront is the source of further waves

Question 8

How was the particle character of light proven?

Question 9

What is the photoelectric effect?

Answer 9

Photoelectric effect:

Photoelectrons (=negative charges) are emitted from matter as a consequence of the absorption of energy from electromagnetic radiation of very short wavelength and high energy.

E_kin = hf - W_ex

Increasing intensity only changes number of e^- emitted, velocity depends on wavelength & frequency.

First discovered when a metal surface was exposed to UV radiation, negative charged particles were emitted from the exposed surface (Hallwachs-effect).