Photoelectric Effect

I’ve taken some video clips (well Miss Horn did) of us trying out the Photoelectric effect as some people might never have seen it. I’m impressed how well it works, thanks to Mr Physics- who cleaned up the zinc plate. It needs polishing every 15 mins or so as it tarnishes very quickly and then wont work. The video of charging it positively and observing no drop in the gold leaf was just too boring to post. Hope you can watch them: I’ll have to try Plan B if not.

The Photoelectric Effect

Particles and Waves Glossary

Click on the read more to get a glossary of the terms for this unit. I will try to update it as I think of more words that I need to add, or try the quizlet for revision

absolute refractive indexthe absolute refractive index (or just the refractive index), n , of a medium is the ratio of the speed of light in a vacuum to the speed of light in the material. (also the ratio of the wavelength of light in a vacuum to the wavelength of light in the medium)
angle of incidencethe angle between the incident ray and the normal.
angle of refractionthe angle between the refracted ray and the normal.
atomic mass units (u)by definition one twelfth of the mass of a carbon-12 nucleus.
atomic numberthe number of protons in an atomic nucleus. It is this number that determines the element and its properties.
binding energythe energy needed to split a nucleus into its separate nucleons (not on the CfE Higher course)
chain reactionwhen a nucleus undergoes fission it releases neutrons that can go on to cause further fission reactions by interactions with other nuclei. If there is a sufficient concentration of suitable nuclei, the process becomes self-sustaining.
coherent wavescoherent waves are waves that have the same frequency, speed and have a constant phase relationship.
collimatorpart of a spectrometer that is used to produce a parallel beam of light.
constructive interferencewhen waves arrive at a point in phase or crest meets a crest and trough meets a trough resulting in a wave of larger amplitude than the individual waves.
critical anglethe angle above which total internal reflections occurs. Or, the maximum value of the angle between the normal and the ray in glass, θ glass, for which refraction can occur.
destructive interferencewhen waves arrive at a point in out of phase or crest meets a trough resulting in a wave of smaller amplitudeas the waves cancel out.
diffractionan effect that causes waves to bend as they go past the end of an obstacle or through a small gap in a barrier.
dispersionthe process of splitting up light into its constituent colours, this can be done with a prism and white light.
electromagnetic wavesthe spectrum of waves that includes radio, visible light, X-rays etc which all have no mass and travel at the speed of light in a vacuum.
excited stateany atomic energy level higher than the ground state.
ferromagneticmaterials in which the magnetic fields of the atoms line up parallel to each other in regions known as magnetic domains.
fissionthe splitting of a large atomic nucleus into smaller fragments, with the resultant release of excess energy.
gold leaf electroscopedevice used to measure small amounts of charge.
gratinga transparent slide of glass or plastic that has a very large number of equally spaced grooves machined on to its surface. Each groove acts as a source for coherent beams of light.
ground statethe lowest energy level of an atom where an electron has the lowest energy level.
induced fissionthe deliberate splitting of a large nucleus caused by the collision of the nucleus with a neutron.
interferencea phenomenon in which two waves superpose to form a resultant wave of greater, lower, or the same amplitude.
ionisation levelthe energy level at which an electron can break free from an atom.
irradiancethe power per unit area of radiation incident on a surface.
isotopesdifferent forms of the same element. The isotopes of an element contain the same number of protons but have different numbers of neutrons. (Many isotopes are unstable and can emit nuclear radiation)
line absorption spectruma spectrum that consists of narrow dark lines across an otherwise continuous spectrum.
line emission spectruma spectrum consisting of narrow lines of light, the position of which depend on the substances producing the light.
magnetic domainsregions in a ferromagnetic material where the atoms are aligned with their magnetic fields parallel to each other.
magnetic fielda magnetic field is a region in which a moving charge experiences a magnetic force.
magnetic polesone way of describing the magnetic effect, especially with permanent magnets. There are two types of magnetic poles - north and south. Opposite poles attract, like poles repel.
mass defect (do not confuse with mass difference)the difference between the mass of a nucleus and the total mass of an  equal number of individual nucleons.
mass differencethe difference in mass between the reactants and products in a nuclear reaction. The resulting mass difference is converted to energy according to the equation E=mc 2 .
mass numberthe total number of nucleons (protons and neutrons) in the nucleus of an atom.
monochromaticradiation consisting of a single frequency.
monochromatic lightlight of one wavelength (and therefore one colour)
normala line drawn at right angles to a surface or the boundary between two different media
nucleonthe general term for protons and neutrons (contained in the nucleus).
nuclidethe nuclei of one particular isotope. These nuclei all have the same atomic number and mass number.
path differencethe difference in path lengths of two sets of waves.
phasedenotes the particular point in the cycle of a waveform.
photocathodethe terminal from which electrons will be emitted due to the photoelectric effect.
photoelectric effectthe emission of electrons from a metal due to the effect of electromagnetic radiation.
photoelectronsfree electrons produced by the photoelectric effect
photoemissionthe emission of electrons from a material caused by light shining on it.
photonthe particle of electromagnetic radiation.
potential differencethe potential difference between two points is a measure of the work done in moving one coulomb of charge between the two points.
principle of reversibilitythe principle of reversibility states that a ray of light will follow the same path in the opposite direction when it is reversed.
prisma prism is a transparent optical element with flat, polished surfaces that refract light. A dispersive prism can be used to break light up into its constituent spectral colours.
quantaa "packet" certain amount, often referring to the energy of photons.
radioactive decay seriesa chain of radioactive decays as a radioactive element changes to eventually become a stable, non-radioactive element.
radioisotopeshort for radioactive isotope.
radionuclideshort for radioactive nuclide.
refractionrefraction occurs when a wave goes from one medium into another. When a wave is refracted, its speed and wavelength change; its frequency remains constant; its direction sometimes changes.
spectrometeran instrument that can make precise measurements of the spectra produced by different light sources.
spontaneous fissionthe random splitting of a large atomic nucleus due to the internal processes within the nucleus. (it does not require neutrons to cause the reaction and so is not of use in a nuclear reactor).
stopping potentialthe minimum voltage required to reduce photoelectric current to zero.
telescopethe part of a spectrometer through which the spectrum is viewed.
threshold frequencythe minimum frequency of electromagnetic radiation that will cause photoemission for a particular substance.
total internal reflectionwhen a ray of light travelling in a more dense substance meets a boundary with a less dense substance at an angle greater than the critical angle, the ray is not refracted but is all reflected inside the more dense substance.
turntablethe stage or platform of a spectrometer on which the grating or prism sits. The turntable has an angular scale on it to allow measurements to be made.
work functionthe minimum energy required to cause photoemission from a substance.
February 2019

New Secret Sign of the Physicist

For years I’ve struggled with the best way to teach force on a moving particle in a field. Tom Balanowski first introduced me to the “slap” method and this year with the help of the 2016-2017 Higher Physics Group we have got it sorted!


Use the Left-hand Slap Rule where the four fingers of the left point in the direction of the magnetic field B and the thumb points in the direction of the moving charge or current, the direction of slapping would be the direction of force F on the conductor.

So how to deal with positive and negative charges. We decided that this method can be used for both. If the charge is negative the slap is the way the palm points. If the charges are positive then use the back of the hand, which is far more Painful

Pain = Positive

Thanks to Amy for these! Note the arrow for the force, should really be coming out of the hand or the way the slap goes; Amy drew this on her hand before I had told her about the × and • -kinaesthetic learner!


Secret sign1

secret back hand



Particles and Waves Resources

Powers of Ten- this was high tech when I was at school!

Since then a few things have moved on, not least with the physics as well as the graphics.

Orders of Magnitude

The class of scale or magnitude of any amount, where each class contains values of a fixed ratio (most often 10) to the class preceding it. For example, something that is 2 orders of magnitude larger is 100 times larger; something that is 3 orders of magnitude larger is 1000 times larger; and something that is 6 orders of magnitude larger is one million times larger, because 102 = 100, 103 = 1000, and 106 = one million

In its most common usage, the amount scaled is 10, and the scale is the exponent applied to this amount (therefore, to be an order of magnitude greater is to be 10 times, or 10 to the power of 1, greater).

Orders of magnitude are generally used to make very approximate comparisons and reflect very large differences. If two numbers differ by one order of magnitude, one is about ten times larger than the other. If they differ by two orders of magnitude, they differ by a factor of about 100. Two numbers of the same order of magnitude have roughly the same scale — the larger value is less than ten times the smaller value.

Source: Boundless. “Order of Magnitude Calculations.” Boundless Physics Boundless, 26 May. 2016. Retrieved 23 Jan. 2017 from

A proton is 3 orders of magnitude larger than a positron or electron.

Below are the updated 2019 versions. Currently the book is divided into the Standard Model, Forces and Particles and Nuclear Radiation in Part 1 and the waves part will be in part 2, which I have yet to finalise. If you want a colour copy, then you’re welcome to print it out at your own cost.on

P&W ANSWERS Now most of the notes are complete I can start working through the answers. I have got these in a jotter, but will plod through them as quick as I can. They are very slow to type up in equation editor.

…and finally the Particles and Waves book 2 is finished.

Particles and Waves Knowledge Organiser P1

Particles and Waves

Particles from the Particles and Waves section- 4 pages+ references (don’t print that one!)
These currently are 5 draft pages

Additional Resources- take your pick

Introduction to Particle Physics

The following two documents are a wonderful summary of the Particles and Waves topic from the Revised Higher course courtesy of George Watson’s College, which is very much the current CfE Higher Course.

Particles & Waves

Here’s a lovely little revision sheet on the Standard Model thanks to Mr Ian Cameron.

Standard Model IC word version

Standard Model IC pdf version

Below are some cracking resources from Sally Weatherly, find her here!

New for 2021 Powerpoints!

Revision and Orders of Magnitude

Orders of magnitude cut out base

The Standard Model

How to tell a MESON from a BARYON (Stewart, K (2017))

MESON- two syllables = 2 quarks (a quark and antiquark pair)

BARYON- three syllables = 3 quarks

Sorting the Fundamental Particles

Standard Model Street

Standard Model Tweet

#Higgs Boson

= fundamental particle, used by HiggsField 2 interact with other particles 2 give them m, causes particles to slow, cannot reach c due to m.

found the sign 2022 is looking good

Charged Particles on Fields

Particle Accelerators


I don’t know who was the original source of some of this material on Physics Resources but thanks! Hope you don’t mind I updated it.


Inverse Square Law

Wave particle Duality



Was this the original Spectra?

Line Spectra


I’ve had to split this as it is too big. The second part will appear after Friday

The pdf obviously doesn’t have the video clips!

Other resources

quantum model of atom

quantum model of atom answers


quantum model of atom Mrs Physics’ model of energy level, to help you remember, not necessarily to teach you Physics!

quantum model of atom answers Mrs Physics’ model of energy level answers. Don’t look at these until you’ve tried them yourself!

These are the tweets from the higher class this 2017. Describe in under 140 characters the following words. Let us know if you can do better. Some of the tweets are a little over as there are no symbols in wordpress that I can find.
TERMDEFINITION (140 characters or less)
#4 FUNDAMENTAL FORCESFundamental forces: interactions that cannot be reduced. There are 4 types. The forces keep all matter together in the universe.
#ANNIHALATEProcess in which a particle and antiparticle unite, annihilate each other, and produce 1 or more photons. Energy and momentum are conserved.
#ANTIMATTERMatter consisting of elementary particles which are the antiparticles of those making up normal matter.
#BARYONA subatomic particle which has a mass greater than or equal to that of a proton.
#BOSONA subatomic particle, such as a photon, which has zero or integral spin. All the force carrier particles are bosons.
#COLOUR Particle has 3 apparently identical quarks but have different properties categorised by colour to satisfy Pauli Exclusion Principle
#ELECTROMAGNETIC FORCE1 of 4 fundamental forces. influencing electrically charged particles. Responsible for electricity, magnetism and light and holds p+ and e- together
#ELECTROMAGNETIC FORCEAffects electrically charged particles. Responsible for electricity, magnetism, & light;holds e- and p+ in atoms; allows atoms to bond to form molecules. Causes objects to be solid
#EXCHANGE PARTICLEParticle that carries forces for strong force – gluon, weak force – W and Z bosons, electromagnetic – photon and gravitational – graviton.
#FERMIONMatter particles e.g. proton, neutron and electron that have a half-integer spin and are constrained by the Pauli Exclusion Principle.
#GLUONA supposed massless subatomic particle believed to transmit the force binding quarks together in a hadron. They mediate the strong force.
#GRAVITATIONAL FORCEA force that attracts any object with mass.
#HADRONA particle made of quarks. Two families: baryons – made of 3 quarks & mesons – made of 1 quark & 1 antiquark. Protons & neutrons are baryons
#HIGGS BOSONfundamental particle, used by Higgs Field, to interact with other particles two give them m, causes particles to slow therefore cannot reach c due to m.
#LEPTONElementary particles, the basic building blocks of matter. Six leptons are in present structure. Varieties are called flavours.
#MESON Are intermediate mass particles that are made of a quark- antiquark pair. Mesons are bosons and could be hadrons.
#MUONA particle similar to the electron, with an electric charge of −1 e and a spin of 1/2, but with a much greater mass. It is classified as a lepton.
#NEUTRINOA neutral subatomic particle. Mass close to zero. Half-integral spin.Rarely reacts with normal matter. 3 types of neutrino are electron, muon and tau.
#POSITRONPositron= antielectron =the antiparticle of the electron has an. Its electric charge is +1 e, a spin of 1/2, same mass as an electron.
#QUARKQuark: a fundamental particle. Quarks combine to form composite particles called hadrons. The most stable hadrons are protons and neutrons.
#SPINAll particles have spin. Can be up or down & has a fixed value which depends on the type of particle. Particles can be right or left handed
#STANDARD MODELTheory concerning electromagnetic, gravitational, strong and weak nuclear interactions and classifying all known subatomic particles.
#STRONG FORCEBinds quarks together to make subatomic particles e.g.protons and neutrons. Holds together the atomic nucleus. Causes interactions between particles that have quarks.
#WEAK FORCEA force that plays a role in things falling apart, or decaying.

Mrs Physics was given a tweet to do too. I think she did very well, exactly 140 characters with spaces!

Prof Aidan Robson (Glasgow University)
Hope no one gets to this stage!

It is not as Mrs B said Mrs H’s Bohring Model, but it is more like a Stewart method of remembering the Bohr model!

quantum model of atom

quantum model of atom answers

Photomultipliers- what the heck are they?


Here are three links to some cracking simulations for this topic

PhET Interactive Simulations
University of Colorado Boulder


Anderson High school Shetland Notes

With grateful thanks to Ms Nancy Hunter from Anderson High School in Shetland. Apparently these have been voted as the best Higher notes.



Online simulations

There is a great simulation from Phet Colorado Physics. It is fantastic and we must support this great site.

PhET Interactive Simulations
University of Colorado Boulder

Photoelectric Effect

Click to Run

This is a great little introduction to Chapter 7 Interference and Diffraction.


A great poster from NPL- measurements are in their care! The poster shows how time keeping has got more and more precise.

Scholar Notes



Mrs Physics

Updated January 2022