Ch 29: The Electron

Question 1

Electron

Answer 1

Particle of tiny mass that orbits the nucleus, negatively charged and has the smallest amount of charge found in nature

Question 2

GJ Stoney

Answer 2

Irish, came up with the word electron

Question 3

Robert Millikan, 1911

Answer 3

American, sound the value of the electrons charge

Question 4

Thermionic Emission

Answer 4

The giving off of electrons from the surface of a hot metal. (Energy gained form heat allows electrons to escape)

Question 5

Cathode rays

Answer 5

Streams of high speed electrons moving from the cathode

Question 6

Cathode ray tube

Answer 6

Produces cathode rays through the process of thermionic emission

Question 7

Properties of cathode rays

Answer 7

• move in straight lines
• cause certain substances to give out light
• have kinetic energy
• can be deflected in electric and magnetic fields
• invisible

Question 8

Function of Y-plates in a cathode ray tube

Answer 8

control vertical movement

Question 9

Function of X-plates in a cathode ray tube

Answer 9

control horizontal movement

Question 10

In an electric field, if an electron is losing potential energy…

Answer 10

it is gaining kinetic energy or eV=1/2mv^(2)

Question 11

Electronvolt (eV)

Answer 11

the amount of energy gained/lost by an electron when it moves through a potential difference of 1 volt (basically just another measure of energy)

Question 12

F in F=qvB stands for

Answer 12

Force on a current carrying conductor in a magnetic field

Question 13

What direction does a beam of electrons move in a magnetic field

Answer 13

Circle, according to FBI, or Fleming’s left hand rule

Question 14

Applications of a cathode ray tube

Answer 14

• television/computer monitor
• Electrocardiogram (ECG), a heart monitor
• Electroencephalogram (EEG), brain monitor

Question 15

The photoelectric effect

Answer 15

The emission of electrons from the surface of a metal by electromagnetic radiation of a certain frequency

Question 16

Photocell/photoelectric cell

Answer 16

A device that conducts electric current when light of a certain frequency shines on it.

Question 17

Current in a photocell is proportional to…

Answer 17

Intensity of light

Question 18

Threshold frequency

Answer 18

For each metal, this is the frequency below which photo emission does not occur, increasing the frequency above this does not affect the current

Question 19

Work function

Answer 19

The min. energy needed to remove the loosest electron from the surface of a specific metal.

Question 20

Photon

Answer 20

bundle of electromagnetic energy

Question 21

Energy of a photon

Answer 21

hf (where h= Planck’s constant)

Question 22

Einstein’s Photoelectric Law

Answer 22

1/2mv^(2) (max)= hf-Φ, i.e. the kinetic energy of the fastest electron emitted = the difference between the energy of photon and the work function of the metal.

Question 23

Applications of photoelectric sensing devices

Answer 23

• burglar alarm

- automatic doors

Question 24

Wilhelm Rontgen, 1895

Answer 24

Discovered x-rays

Question 25

X-rays

Answer 25

high frequency electromagnetic radiation produced when high-speed electrons strike a a metal with a high melting point

Question 26

Penetrating power of x-rays

Answer 26

Penetrating power is directly proportional to the frequency of the x-rays which is directly proportional to the voltage across the tube.
…Penetrating power is dir. pro. to voltage across the tube

Question 27

Properties of x-rays

Answer 27

• penetrate materials
• can produce florescence in certain materials
• electromagnetic radiation with wavelength of 10^(-9) to 10^(-15) m
• can cause photoemission
• not deflected in electric or magnetic fields
• affect photographic emulsions
• ionises materials
• produces interference patterns and undergoes diffraction

Question 28

Uses of x-rays

Answer 28

1. Medicine: x-ray photographs, destroy cancer cells

2. Industry: detect cracks, flaws ,welds and can photograph inside machines

Question 29

Hazards of x-rays

Answer 29

x-rays are ionising radiation and … have a harmful effect on human tissue

Question 30

Hot cathode x-ray tube

Answer 30

produces x-rays through the use of thermionic emission