ch22

Question 1

photon 1

Answer 1

light arrives in particles called photons

Question 2

photon 2

Answer 2

the special name given to a quantum of energy when the energy is in the form of electromagnetic radiation

Question 3

quanta

Answer 3

Discrete packets or quantities of energy of electromagnetic radiation

Question 4

The energy E carried in each quantum is given by

Answer 4

E=hf=hc/λ where h= plank constant=6.63*10^-34

Question 5

The momentum p equation

Answer 5

p = E/c

Question 6

electronvolt (eV)

Answer 6

energy gained by an electron when it is accelerated from rest in a vacuum through a potential difference of one volt. 1 eV = 1.60 × 10^–19 J

Question 7

Photoelectric emission

Answer 7

the release of electrons from the surface of a metal when electromagnetic radiation is incident on its surface. The electrons emitted are referred to as photoelectrons

Question 8

work function

Answer 8

the minimum amount of energy required to release an electron from the surface of a metal during photoelectric emission////////// minimum photon energy required to release an electron

Question 9

threshold frequency

Answer 9

The minimum frequency of incident radiation required to cause photoelectron emission from the surface of a particular metal: hf0 = φ.

Question 10

threshold wavelength

Answer 10

The maximum wavelength corresponding to the threshold frequency to give rise to photoelectric emission

Question 11

photoelectric effect summary

Answer 11

1. if the energy of a photon> work function of an electron, an electron will be emitted
2. Photoemission takes place only if the frequency of the incident radiation is above a certain minimum value called the threshold frequency f0
3. there is a one to one interaction between photons and electrons
4. If photoemission takes place, it does so instantaneously. There is no delay between illumination and emission

Question 12

loss in kinetic energy equation

Answer 12

loss in kinetic energy = gain in potential energy = charge of electron × potential difference

Question 13

explain why the maximum kinetic energy of photoelectrons is independent of intensity, whereas the photoelectric current is proportional to intensity

Answer 13

The maximum kinetic energy of the photoelectrons is independent of the intensity of the incident radiation, This is because each electron can only absorb one photon

Photoelectric current is proportional to the intensity of the radiation incident on the surface of the metal. This is because intensity is proportional to the number of photons striking the metal per second

Question 14

photoelectric equation

Answer 14

photon energy = work function energy + maximum kinetic energy of photoelectron//// hf = hf0 + 1/2 me vmax^2 where hf0 work function and the other is maximum kinetic energy of
photoelectron

Question 15

de Broglie wavelength.

Answer 15

λ = h/p

Question 16

the energy hf of the photon

Answer 16

hf = E2 –E1, where E2 is the energy of the higher level and E1 is that of the lower

Question 17

the wavelength of the emitted radiation

Answer 17

λ = hc/ΔE

Question 18

discrete energy levels

Answer 18

Certain specific energy levels that the electrons in an atom can have; they cannot have energies in between these levels.

Question 19

Describe the appearance of a visible line emission spectrum, as seen using a diffraction
grating.

Answer 19

mostly dark/dark background B1
coloured lines

Question 20

Briefly describe two phenomena associated with the photoelectric effect that cannot be explained using a wave theory of light.

Answer 20

• frequency below which electrons not ejected
• maximum energy of electron depends on frequency
• maximum energy of electrons does not depend on intensity
• instantaneous emission of electrons