Atomic Physics (Theory)

Charge of an electron

-1.6 x 10-19 C

Mass of electron

9.1 x10-31 kg

What does an electron orbit?

Nuclei

Who named the electron?

G.J Stoney

Who measured the charge of an electron?

Milikan

Who measured the mass of an electron

J.J Thomson

Why do we use the electron-Volt?

Joule is too large of a unit of energy at the atomic level

How to convert eV to J?

Multiply by 1.6x10-19

How to convert J to eV?

Divide by 1.6x10-19

What is GeV?

Giga-electronvolts

What is keV?

Kilo-electronvolts

What is MeV?

Mega-electronvolts

Draw a diagram of Thermionic Emission

Thermionic emission (Definition)

The emission of electrons from the surface of a metal by heat

Who discovered thermionic emission?

Thomas Edison

Explain thermionic emission

Voltage from LTDCPS pushes electricity through filament which gets hot and electrons are boiled off. They're attracted to the positive of the HTDCPS and pass through the disk if there's a hole. Electrons strike glass and the kinetic energy is converted to light

What colour of light is usually emitted by thermionic emission?

Usually green light

Where must thermionic emission take place in?

Vacuum tube

Why would thermionic emission not work outside of a vacuum?

Electrons would collide with air molecules which would stop/slow them if there was air in the tube

What were beams of electrons originally known as?

Cathode rays

Where is thermionic emission used in? (4)

Televisions. Cathode ray oscilloscopes (CRO). ECG/EEG monitors. Radar displays

What is a Cathode ray oscilloscopes (CRO)?

Heart rate monitor

What is a ECG/EEG monitors?

Monitor brain waves

Draw a diagram of J.J Thomson's e/m experiment (Deflection of cathode rays in electric fields & magnetic fields)

Explain Thomson's e/m experiment

Beam of electrons bent downwards with an electric field and up with a magnetic one. From B E and V he measured e/m the charge to mass ratio of the electron.

Why could J.J Thomson calculate the mass of the electron?

Milikan already measured e

Draw a cathode ray tube

Explain the cathode ray tube

Electrons boiled off. Collimating anodes accelerate electrons across and produce a narrow beam. Screen coated with phosphors which convert the kinetic energy of the electrons to light energy

How is the brightness of the beam controlled (Cathode Ray Tube)?

Grid can be made negative to control amount of electrons being attracted across

How is the movement of the beam (pixel by pixel) controlled?

X-plates Y-plates can be made positive and negative by the signal from the aerial

How many colours in TV?

Red Green Blue

Function of conductive coating

Recycles electron

Photoelectric emission (Definition)

Emission of electrons from the surface of a metal by electromagnetic radiation of a suitable frequency

Who discovered photoelectric emission?

Heinrich Hertz

Example of black-body radiation

Stars

Formula for the energy of a photon

E = hf

What does h stand for (Formula for the energy of a photon)?

Planck's constant

What does E stand for (Formula for the energy of a photon)?

Energy of photon

What does f stand for (Formula for the energy of a photon)?

Frequency of photon

Photon (Definition)

A quantum of electromagnetic energy

Draw a diagram of a photon liberating an electron from an atom

How does light travel, get emitted, get absorbed?

As photons

Explain the photoelectric effect according to Einstein

If a photon of light has less than the required energy to liberate an electron then nothing would happen. When a photon has exactly the energy required it would liberate the electron. If the photon had more energy than the required amount it would liberate the electron and the extra would be given to the liberated electron as kinetic energy

Threshold frequency (Definition)

Minimum frequency of electromagnetic radiation required to liberate an electron from the surface of a metal

Einstein's photoelectric law Formula

E = ϕ + Ek hf=hfo +1/2mv2 hc/λ = (hc/λo)+1/2mv2

What is E? (Einstein's photoelectric law Formula)

Energy of photon

What is ϕ? (Einstein's photoelectric law Formula)

Work function

What is Ek? (Einstein's photoelectric law Formula)

Kinetic energy

What is h? (Einstein's photoelectric law Formula)

Planck's constant

What is f (Einstein's photoelectric law Formula)

Frequency of photon

What is fo? (Einstein's photoelectric law Formula)

Threshold frequency

What is m? (Einstein's photoelectric law Formula)

Mass of electron

What is v? (Einstein's photoelectric law Formula)

Velocity of electron

What is c (Einstein's photoelectric law Formula)

Speed of light

What is λ? (Einstein's photoelectric law Formula)

Wavelength of photon

What is λo? (Einstein's photoelectric law Formula)

Threshold wavelength

What is work function in Einsteins photoelectric law?

Energy needed to kick out an outer shell electron

When are X-Rays produced?

When high-speed electrons are stopped by a dense metal target

Who discovered X-rays?

Wilhelm Röntgen

Draw a diagram of a hot cathode X-ray tube

Explain a hot cathode X-ray Tube

Electrons emitted by themionic emission and attracted at high speeds to the positive of the HTDCPS. Stopped by tungsten and their kinetic energy is converted into high energy electromagnetic waves (x-rays)

Features of tungsten

Very dense. High melting point

What is most of the kinetic energy in an x-ray tube converted to?

Heat

Function of copper block and cooling fins

Dissipates heat energy

What is the number of x-rays/intensity directly proportional to?

Number of electrons

How is the number of electrons controlled in a x-ray?

Temperature of the cathode

How is the temperature of the cathode controlled in an x-ray tube?

Voltage of LTDCPS

What is the energy of an x-ray directly proportional to?

Kinetic energy of an electron

What is the kinetic energy of an electron directly proportional to in an x-ray tube?

Voltage of HTDCPS

Higher LTDCPS means what in an x-ray tube?

More x-ray rays

Higher HTDCPS means what in an x-ray tube?

More energetic x-rays

Function of lead shielding in an x-ray tube

Protects the operator

What is x-ray production the opposite of?

Photoelectric effect

Properties of x-rays (3)

Electromagnetic waves. Low ionisation. High penetration

Uses of x-rays (3)

Internal photographs of the human body. Checking for fractures in metal structures e.g. oil rig legs. Curing cancer (radiotherapy)

Hazards of x-rays (2)

Cancer. Mutations

Draw a diagram of a discharge tube

Draw a diagram of a discharge tube sketch graph

Explain a discharge tube (1 of sketch graph)

At low voltages a small current flows. Current due to ions and electrons produced by radiation. Voltage is increased more ions/electrons reach electrodes increasing the current.

Explain a discharge tube (2 of sketch graph) (Why does the graph stop increasing for some time?)

All ions/electrons produced are reaching electrodes and increasing the voltage has no effect on the current

Explain a discharge tube (3 of sketch graph)

Voltage becomes big enough that ions are travelling so fast that they create more ions by collision. These can produce even more ions increasing the voltage and the current to rise

What radiation produces ions and electrons in a discharge tube?

X-rays or cosmic radiation

What is a current in a gas called?

Discharge

What are the conditions for a gas to produce electromagnetic radiation?

Low pressure and high voltage

What happens when a gas is at a low pressure with a high enough voltage?

Gas emits electromagnetic radiation

What is the electromagnetic radiation produced by a gas called?

Glow discharge

What is a discharge tube also known as?

Fluorescent

Explain how electrons become excited

Electrons occupy lowest energy levels in atoms. However if supplied with heat or electricity electrons become excited. This is unstable and the electron falls back releasing energy as electromagnetic radiation

Formula for excited electrons

Ex-Ey=hf

What is emitted by a substance which has a small number of energy levels?

Line emission spectrum

What is a line emission spectrum?

Limited number of frequencies of light will be emitted

Example of a substance with a small number of energy levels

Monatomic gas e.g. He

What is emitted by a substance which has more energy levels?

Band emission spectrum

What is a band emission spectrum?

More frequencies of light emitted

Example of a substance with more energy levels

Polyatomic gas e.g. O2

What is emitted by a substance which has a lot of energy levels?

Continuous emission spectrum

What is a continuous emission spectrum?

Many many frequencies of light is emitted

Example of a substance with a lot of energy levels

Solids and liquids

What is the reverse of an emission spectrum?

Absorption spectrum

What are absorption spectra used for?

Identify unknown substances