Transcript Extended Questions- The Answers

Extended QuestionsThe Answers
Higher Physics
What is meant by “coherent”
waves?
 Same
speed
 Same frequency
 In Phase
Explain in detail what
“photoelectric emission” is?
 Photoelectric
emission is when an electron
is ejected from the surface of a material by
a photo of light which has frequency
greater than the threshold frequency of the
material, or energy greater than the work
function.
What is a “photoelectric
current”?
 Is
when an electric field ( or Potential
difference ) is applied across the area
where a photoelectron has been ejected.
This electron experiences a force and
accelerates. This moving charge is a
photoelectric current.
What is meant by the “work
function”?
 Work
function is the minimum energy
required to release an electron for the
surface of a metal
Explain what is meant by
“quantised energies”?
 Discrete
energy or packets of energy.
Explain in detail how an emission
spectrum is produced.
 When
an electron is in an excited state it
will spontaneously make a transition to a
lower energy state and release a photon of
light. The difference in energies will be
equal to the energy of the photon. From
E=hf the corresponding frequency can be
gained. This transition would appear as
line of colour against a black back.
Explain in detail how an absorption
spectrum is produced.
 When
a material receives a continuous
spectrum of light, some of the frequencies
of light (and the energies E=hf) may
correspond to energy levels within the
atom. If an electron absorbs a photon of a
particular energy it makes an upward
transition to a higher energy level. The
absence of this photon would be
noticeable as a black band on the full
spectrum.
What does “laser” stand for?
 Light
 Amplification
 Stimulated
 Emission
 Radiation
of
due to the
What is meant by the term
“population inversion”
 When
most (or all) of the electrons are
excited to an energy level above the
ground state.
Explain in detail how a laser
works?
 Pump
laser to excite electrons to desired
energy level (population inversion)
 Release photon with equal energy.
 This causes electrons to make downward
transition. Releasing more photons
 All photons in Phase and moving in the
same direction.
What is meant by the term
“doping”?
 The
process of adding impurities to a
semiconductor material.
Explain in detail how a n-type
semiconductor material is formed
 Silicon,
4 outer electrons, tight covalent
bond. No free charge carriers.
 Dope with Arsenic, 5 outer electrons
 4 bond allowing 1 free charge carrier.
 As charge carrier is electron, n-type
material formed
 Nb. Overall charge not changed
What is the depletion layer
and how is it formed?
 In
this region there are no free charge
carriers.
 Formed when electrons fill up holes
around the p-n junction.
A diode is connected forward bias.
Explain in detail if and how it conducts.
 In
forward bias(n type to neg end of bat)
electrons given enough energy to
overcome the depletion layer. This allows
for a current to flow through the depletion
layer, remove it.
A diode is connected reverse bias.
Explain in detail if and how it conducts.
 In
reverse bias the (n-type to pos end) the
potential causes a movement of charge
carriers away from the depletion layer,
making it larger. This makes it even more
difficult to get a current to flow through it.