Electromagnetic Radiation and Quantum Phenomena

Question 1

What is a photon?

Answer 1

A discrete packet of electromagnetic energy

Question 2

What is a quantum of energy?

Answer 2

A small packet of energy

Question 3

What is the threshold frequency?

Answer 3

The minimum frequency of radiation to release electrons from the metals surface.

Question 4

What does the photoelectric effect show about electromagnetic radiation?

Answer 4

That it has particle properties

Question 5

What is work function?

Answer 5

The minimum energy to release an electron from the surface of a metal

Question 6

What is the equation for the maximum kinetic energy of the electron released?

Answer 6

1/2 m(vmax)^2 = hf- work function

Question 7

A negatively charged and freshly cleaned zinc plate will do what?

Answer 7

It will lose electrons if ultraviolet radiation is incident on it

Question 8

The diffraction of electrons by graphite shows what?

Answer 8

That electrons have wave properties

Question 9

What is a conclusion of the photoelectric effect that relates to intensity and maximum KE?

Answer 9

The intensity of radiation is the amount of energy per second hitting an area of the metal.
The maximum kinetic energy of the photoelectrons is unaffected by varying the intensity of the radiation.

Question 10

What is a conclusion of the photoelectric effect relating to KE and frequency?

Answer 10

The photoelectrons are emitted with a variety of kinetic energies ranging from zero to some maximum value.
This value of maximum kinetic energy increases with the frequency of the radiation.

Question 11

One photon of frequency f may release what?

Answer 11

One electron

Question 12

What is a conclusion of the photoelectric effect relating photoelectrons and intensity?

Answer 12

The number of photoelectrons emitted per second is proportional to the intensity of the radiation.

Question 13

What is a conclusion of the photoelectric effect relating threshold frequency?

Answer 13

For a given metal, no photoelectrons are emitted if the radiation has a frequency below a certain value- called the threshold frequency.

Question 14

The electrons emitted during the photoelectric effect are called what?

Answer 14

Photoelectrons

Question 15

What are the principal features of the spectrum from excited gas atoms?

Answer 15

Photons have definite wavelengths
So photons have discrete energies
Photons are emitted when electrons move down from one level to another
The energy gaps between energy levels are fixed.

Question 16

Explain the term work function

Answer 16

The minimum energy required to remove an electron from a metal

Question 17

Why does maximum kinetic energy not change when the intensity of radiation is increased?

Answer 17

A photon gives up all of its energy in one collision

Question 18

Why does the number of photo electrons emitted per second increased if the intensity of radiation is doubled?

Answer 18

Because increased intensity means that the number of incident photons per second is increased.

Question 19

What is an example of electrons acting like particles?

Answer 19

Deflection of electrons in an electric or magnetic field.

Question 20

What happens in a fluorescent light tube when it is in operation?

Answer 20

Mercury atoms are excited by electron impact.

They then emit light upon relaxation which is predominantly ultraviolet.

Question 21

What is the phosphorus coating on the inside of a fluorescent tube for?

Answer 21

It absorbs the ultraviolet light from the mercury atoms and emits light with a longer wavelength in the visible region.

Question 22

What is a suitable range of wavelengths for gamma?

Answer 22

Between 10^-15 and 10^-12

Question 23

When the photoelectric effect is connected to a circuit, how does increasing the intensity of the incident radiation affect the current?
Why?
What is assumed?

Answer 23

Increases it.
Increasing intensity increases number of photons per second
Which increases the number of electrons released per second
Current = rate of flow of charge
Therefore current increases.
Assuming one photon liberates one electron.