Module 1 Flashcards
What is the definition of work function?
It is the minimum energy needed to remove an electron from the surface area of a metal.
Work function units
Joules (J)
What is the definition of threshold frequency?
It is the minimum frequency needed to remove an electron from the surface of a metal
What do the terms hf, and Ekmax in the photoelectric equation?
hf - photon energy
- work function
Ekmax - maximum kinetic energy of the photoelectron
What is the electron volt?
An electron volt (1 eV) is the energy gained by an electron moved across a potential difference of 1 volt.
How do you convert between electron Volts and Joules?
1eV = 1.6x10-19 J
What is excitation?
An (orbital) electron moves up from one energy level to another
What is an excited atom?
An atom in which an (orbiting) electron is raised up to a higher energy level
What is ionisation (in context of gas discharge tube)
When an electron is removed from an atom
What is ionisation energy?
The energy required to completely remove an electron from an atom in its ground state
What is the ground state of an atom?
The lowest energy state of an atom
What is fluorescence?
high energy (UV) photons are absorbed and lower energy photons (longer wavelength) are emitted in the visible part of spectrum
What is meant by wave particle duality?
particles (e.g. electrons, light) behave sometimes as particles and sometimes as waves
What is an experiment showing waves behaving as particles?
Photoelectric effect
What is an experiment showing particles behaving as waves?
Electron diffraction
Equation of momentum?
mass x velocity (p = mv)
What are the units of momentum?
kg ms-1
What is an electric current?
Rate of flow of charge
What is potential difference?
The work done (energy transferred) per unit charge
What is Ohm’s Law?
Current is directly proportional to potential difference, providing the temperature and other physical conditions remain the same
What is an ohmic conductor?
A conductor where I is directly proportional to V
What is a non-ohmic conductor?
A conductor where I is not directly proportional to V
What is the resistance of a voltmeter and ammeter?
- Voltmeter resistance is very large ( or infinite)
- Ammeter resistance is very small (or zero)
What do the terms , R, A and L mean in resistivity equation?
- is resistivity
- R is resistance
- L is length and
- A is the cross-sectional area
What is definition of resistivity?
Resistivity ρ is defined as ρ = RA/L where R is the resistance of material length L, and cross-sectional area A
What are the units of resistivity?
m
What is superconductivity?
A material with zero resistivity
What are the uses of superconductors?
- MRI scanners
- Maglev trains
- Particle accelerators e.g. Large Hadron Collider
What is the critical temperature?
The temperature at, and below which, a material has zero resistivity (or resistance)
What is EMF?
- actual energy provided by the battery (or cell) per unit charge
OR - the terminal potential difference across the battery when no current is flowing
What is internal resiitance
- the hindrance to the flow of charge in the battery
OR - the loss of potential difference per unit current
What is “lost” potential difference?
potential difference dropped across the internal resistance of a cell (or battery)
How does the resistance of a thermistor and wire change with increasing temperature?
- Thermistor : resistance decreases as temperature increases
- Wire : resistance increases as temperature increases
How does the resistance of and LDR changes with an increasing light intensity?
Resistance decreases with increasing light intensity
What is the potential difference across a diode in forward bias?
A potential difference of 0.6V is dropped across a diode in forward bias
What is the potential difference across cells in series and parallel?
- In series, potential difference of each cell adds up
- In parallel, potential difference is the same
What is the difference between a.c. and d.c current?
- alternating current : direction of current is continually changing
- direct current : current always flows in same direction
What is the defintion of rms current and rms voltage?
- rms current (Irms) : the equivalent dc current that produces the same heating effect in the same resistor
- rms voltage (Vrms) : the equivalent dc voltage that produces the same heating effect in the same resistor
What are the peak values (of current or voltage)?
The maximum current (or voltage) which is the same in either direction
What are peak to peak values (of current or voltage)
the difference between the peak value one way and the peak value in the opposite direction (i.e twice the peak value)
What is a time period?
Time for one complete oscillation
What is an isotope?
an atom with the same number of protons but a different number of neutrons
What is the equation for specific charge?
C kg-1
What is the particle with the greatest specific charge?
electron
What is an alpha particle, a beta particle and gamma particle
alpha particle : 2 protons and 2 neutrons (a helium nucleus)
beta particle : a fast moving electron
gamma particle : a high energy photon
what are four different forces and their corresponding exchange particles?
strong force : gluon or pion
weak force : W particle
Electromagnetic force : virtual photon
Gravitational force : graviton
What is pair production?
When a gamma photon changes into a particle and its corresponding antiparticle.
What is annihilation?
When a particle and its antiparticle meet, they destroy each other and release 2 gamma photons
What is antimatter?
Particles with the same rest mass but equal and opposite charge (if they are charged) as corresponding particle.
What exchange particles transfer?
momentum; energy; force; sometimes charge (can only be transferred in a weak interaction)
What are the differences between hadrons and leptons?
- Hadrons : feel the strong force
- Leptons : do not feel the strong force
What is the general quark composition of a baryon, anti baryon and a meson?
Baryon: qqq
Anti-Baryon: -q-q-q
Meson: q-q
What do baryon’s decay into?
Protons
What is the most stable baryon?
Proton
What is conserved in strong and weak interactions?
All interactions: Energy, Momentum, Charge, Baryon Number, Lepton Number
Strong Force only : strangeness
What is a strange particle?
A particle that contains at least q strange quark or anti-quark
What is a chracteristic of a strange quark?
It has a strangeness of -1.
