Question Corrections

Question 1

Why is a star considered to be a black body?

Answer 1

• Does not reflect radiation
• Absorbs heat radiation and emits radiation at all wavelength

Question 2

Temperature curves for stars

Answer 2

• Intensity’s peak lies in shorter wave region
• Shorter wavelengths indicate a hotter temperature

Question 3

Calculating number of photons released given frequency and power

Answer 3

E = hf
No. photons = P/hf

Question 4

Define Coherent Light and example of source

Answer 4

Light that is the same wavelength travelling in phase
e.g. Laser

Question 5

Summarise Bohr’s Model

Answer 5

• Electrons have circular orbits
• The greater the radius, the more energy the electron has
• Only some energy levels have stable orbits
• As electrons drop between levels, the lose energy in photons

Question 6

Stopping voltage

Answer 6

Ek –> stopping V
W = Vq
V = W/q

Question 7

Discuss how Einstein’s evaluation of the photoelectric effect changed our understanding of light

Answer 7

• Einstein suggested the light was quantised/particle nature of light
• and that it gave up all its energy when absorbed by a metal or none of its energy if the metal’s threshold frequency was not met (all or nothing)
• Previous thought was that an electron could absorb enough energy from continuous light until it has sufficient to be ejected