3.3 Collisions of electrons with atoms

Question 1

What is an ion?

Answer 1

» A charged atom

Question 2

How is an ion formed?

Answer 2

» From an uncharged atom by adding or removing electrons from the atom

Question 3

What does adding electrons make the atom?

Answer 3

» Negatively charged

Question 4

What does removing the electrons do?

Answer 4

» Form a positive ion

Question 5

What is ionization?

Answer 5

» A process of creating ions, when the electrons gain enough energy to be removed from the atom entirely to produce unbalance charges

Question 6

What are the 3 radioactive radiations?

Answer 6

» Alpha
» Beta
» Gamma

Question 7

When does Alpha, Beta , Gamma create ions?

Answer 7

» When they pass through substances and collide wit the atoms of the substance

Question 8

What is the ionization energy of a gas atom?

Answer 8

» eV

Question 9

What is the electron volt?

Answer 9

» Unit of energy equal to the work done when an electron is moved through a pd of 1V

Question 10

What is the value of electron volt?

Answer 10

» 1.6 x 10^-19 J

Question 11

What is excitiation?

Answer 11

» An electron in an energy level or an orbiting electron shell is given energy usually by collision to move to a higher energy level

Question 12

When does excitation happen?

Answer 12

» At certain energies

Question 13

What happens if the colliding electron does not have enough kinetic energy?

Answer 13

» It is deflected by the atom, with no overall loss of kinetic energy

Question 14

What happens if a colliding electron loses all its kinetic energy when it causes excitation?

Answer 14

» The current due to the flow of electrons through the gas is reduced

Question 15

When does ionisation occur?

Answer 15

» If the energy of the free electron is greater than the ionisation energy

Question 16

What happens when an electron becomes de-excited?

Answer 16

» Will returns to its ground position and therefore release the energy it gained in the form of a proton

Question 17

Why is the excitation always less then the ionisation energy of the atom?

Answer 17

» Because the atomic electron is not removed completely from the atom when excitation occurs

Question 18

Why is the kinetic energy a maximum?

Answer 18

» Work function is the minimum amount of energy required to remove an electrons

Question 19

Explain why there is a current only if the frequency of the radiation is above a certain value?

Answer 19

» Energy of the photon is greater than the work function therefore electrons are emitted

Question 20

What happens to the current if you increase the intensity of the electromagnetic radiation?

Answer 20

» More photons per second are released
» Greater current

Question 21

What is the effect on the stopping potential if the frequency is increased?

Answer 21

» Energy of the photon is greater
» This would cause the stopping potential to increase
» As maximum kinetic energy of the electrons would be greater
» More work done is needed

Question 22

What is the ground state?

Answer 22

» When electrons are in their minimum energy state

Question 23

What are the differences between excitation and ionisation?

Answer 23

» Both receive the exact amount of energy required for the process to happen
» Excitation promotes an orbital electron to a higher energy level
» Whereas ionisation causes the electron to leave the atom completely

Question 24

Explain why only photons of a certain frequency cause excitation in a particular atom?

Answer 24

» There are discrete energy level
» Electrons need to absorb an exact amount of energy to excite
» Photons need to have a certain frequency to provide this energy
» All of the energy is absorbed when the electron excites

Question 25

What is kinetic energy equal to?

Answer 25

» E x v

Question 26

Why can a gas atom not absorb energy from a slow moving electron?

Answer 26

» Electron doesn’t have sufficient energy to excite or ionise the atom and so cannot be absorbed

Question 27

When happens when an electron collides with a gas atom and doesn’t cause it to ionise?

Answer 27

» Electron in the atom moves up a level

Question 28

Why is the mercury atom at low pressur?

Answer 28

» Vapor must not completely absorb the electrons

Question 29

Why do the emitted photons have specific wavelengths?

Answer 29

» Electromagnetic radiation is emitted when an electron falls
» From one fixed level to another fixed level
» Giving the photon a discrete amount of energy

Question 30

What does it mean by an excited atom?

Answer 30

» An electron in its lower energy state promotes to a higher energy level, causing the atom to gain energy