3.2- MORE ABOUT PHOTOELECTRICITY

Question 1

What did Max Plank suggest at the end of the 19th century?

Answer 1

energy of each vibrating atom is quantised

Question 2

What does quantised mean?

Answer 2

only certain levels of energy are allowed

Question 3

What did Max Plank say about energy?

Answer 3

energy could only be in multiples of a basic amount, or quantum, hf

Question 4

What did Max Plank imagine each energy level to be like?

Answer 4

rungs of a ladder, with each atom absorbing or emitting radiation when it moved up or down a level

Question 5

What does the average kinetic energy of a conduction electron depend on?

Answer 5

temperature of the metal

Question 6

In what order it the work function of a metal?

Answer 6

10^-19

Question 7

Whats happens to the K.E. of an electron when it absorbs a photon?

Answer 7

its K.E. increases by an amount equal to the energy of the photon

Question 8

What can happen if the energy of a photon absorbed by an electron exceeds the work function?

Answer 8

conduction electron can leave the metal

Question 9

What happens when an electron absorbs a photon but it does not leave the metal?

Answer 9

it collided repeatedly with other electrons and positive ions, and it quickly loses its extra K.E.

Question 10

What is a vacuum photocell?

Answer 10

glass tube that contains a metal plate (photocathode), and a smaller metal electrode (anode)

Question 11

What happens when a light of frequency greater than the threshold frequency is for the metal is directed at the photocathode of a vacuum photocell?

Answer 11

electrons are emitted from the cathode and are attracted to the anode

Question 12

What can the microammeter in the circuit of a vacuum photocell be used to do?

Answer 12

used to measure the photoelectric current

Question 13

What is the current recorded from the microammeter in the circuit of a vacuum photocell proportional to?

Answer 13

number of electrons per second that transfer from the cathode to the anode

Question 14

What is the equation for the number of photoelectrons per second that transfer from the cathode to the anode? (vacuum photocell)

Answer 14

I/e

I- photoelectric current
e- charge of the electron

Question 15

What is the photoelectric current proportional to in a vacuum photocell?

Answer 15

intensity of the light incident on the cathode

Question 16

What is light intensity a measure of?

Answer 16

energy per second carried by the incident light

Question 17

What is the energy per second carried by the incident light proportional to? (vacuum photocell)

Answer 17

proportional to the number of photons per second incident on the cathode

Question 18

What is the number of photoelectrons emitter per second proportional to?

Answer 18

intensity of the incident light

Question 19

Why is the number of photoelectrons emitter per second proportional to the intensity of the incident light?

Answer 19

each photoelectron must have absorbed one photon to escape from the metal surface

Question 20

What does the intensity of the incident light not affect?

Answer 20

the maximum K.E. of a photoelectron

Question 21

Why does the intensity of the incident light no affect the maximum K.E. of a photoelectron?

Answer 21

no matter how intense the incident light is, the energy gained by a photoelectron is due to the absorption of one photon only

Question 22

How can the maximum K.E. of the photoelectrons emitted for a given frequency of light be measured?

Answer 22

using a photocell

Question 23

On a graph what is the kinetic energy?

Answer 23

y

Question 24

On a graph what is the frequency?

Answer 24

x

Question 25

On a graph what is Planck’s constant?

Answer 25

gradient

Question 26

On a graph what is the NEGATIVE work function?

Answer 26

y-intercept

Question 27

On a graph what is the threshold frequency?

Answer 27

x-intercept

Question 28

What would the graph for the photoelectric effect be set up like?

Answer 28

K.E. against frequency