2-2: The nature of Matter

Question 1

Explain Planck’s constant

Answer 1

• Energy can be gained or lost only in integer multiples of h*nu
• where n is an integer (1, 2, 3, . . .), h is Planck’s constant, and nu is the frequency of the electromagnetic radiation absorbed or emitted.

Question 2

Explain Planck’s Constant

Answer 2

• 6.626 x 10^-34 J • s

Energy can be gained or lost only in integer multiples of h• nu

Question 3

What is the definition of quantisized?

Answer 3

• can occur only in discrete units of size h•nu
• Each of these small “packets” of energy is called a quantum.
• A system can transfer energy only in whole quanta. Thus energy seems to have particulate properties.

Question 4

What are photons?

Answer 4

• proposed that electromagnetic radiation is itself quantized.
• Einstein suggested that electromagnetic radiation can be viewed as a stream of “par‑ ticles” called photons
  
  • The energy of each photon
    
    • E_photon = h•nu = hc/lambda
  • where h is Planck’s constant, nu is the frequency of the radiation, and lambda is the wavelength of the radiation.

Question 5

What is the photoelectric effect?

Answer 5

• refers to the phenomenon in which electrons are emitted from the surface of a metal when light strikes it.
• Observations characterize the photoelectric effect:
  
  1. Studies in which the frequency of the light is varied show that no electrons are emitted by a given metal below a specific threshold frequency n0 .
  2. For light with frequency lower than the threshold frequency, no electrons are emitted, regardless of the intensity of the light.
  3. For light with frequency greater than the threshold frequency, the number of electrons emitted increases with the intensity of the light.
  4. For light with frequency greater than the threshold frequency, the kinetic energy of the emitted electrons increases linearly with the frequency of the light.