Physics - Paper 3 only

AQA

systematic error

error due to equipment or setup e.g. parallax, zero, calibration

random error

error due to any other factor e.g. observer, readability, external factors

accuracy

how close a measurement is to the true value

precision

how closely repeated readings agree with each other

repeatability

the consistency of repeated measurements - same person, lab, method

reproduceability

the consistency of repeated measurements - same method, different lab, person

sensitivity

large change in output for a small change in input

resolution

the smallest change in the quantity being measured that gives a perceptible change in the reading

uncertainty

the interval within which the true value can be expected to lie, with a given level of confidence or probability

discharge tube

tube with gas at low pressure with a high voltage across it, used to demonstrate the emission of cathode rays due to an E field

negative electrode

cathode

positive electrode

anode

cathode ray

a fast-moving beam of electrons formed from a CRT (electron gun in a low-pressure gas tube)

how does a discharge tube work

the strong electric field created by the p.d. ionises gas atoms by pulling off electrons. They accelerate towards the cathode, colliding with it and knocking off a shower of electrons, which accelerate towards the anode, ionising/exciting gas atoms. The de-excitation causes emission of visible and UV photons

thermionic work function

the minium energy required to free an electron from the surface of a metal plate by thermionic emission

crossed fields

method used by JJ Thompson to calculate e/m using perpendicular B and E fields at the right strength to leave a beam of electrons undeflected

how did Thompson estimate the order of magnitude of e?

using a cloud chamber

fine beam tube

a low pressure gas-filled tube used to determine e/m with an external B field (by finding r of the circular path)

quantised

a quantity that can only take discreet values

black body

a body that absorbs all radiation incident upon it and reflects none (a perfect absorber and emitter). The energy emitted at each wavelength is dependent on surface temperature

Compton effect

the transfer of momentum and energy when matter interacts with a photon

corpuscular theory

light is composed of particles (corpuscles) which travel in straight lines, used to explain reflection, refraction and sharp shadows (Newton)

EM wave

a transverse wave of electic and magnetic fields at right angles to each other and to the direction of propagation

electron gun

used in CRTs to produce a narrow beam of electrons by thermionic emission

Huygens' principle

every point on a wavefront acts as a source of secondary wavelets (that propagate at the same speed as the original wave)

inertial frame of reference

frame of reference that does not accelerate relative to any other frame of reference. A FoR in which Newtons laws hold.

interferometer

an instrument that uses wave interference to determine the origin or path of a wave

length contraction

reduction of length of an object relative to the observer due to special relativity

Lorentz factor (γ)

(1-v²/c² )^(-1/2)

proper length

length of an object as measured by an observer stationary w.r.t the object (maximum length)

proper time

time interval as measured by an observer in the same frame of reference as the events (minium time)

quantum tunneling

an effect caused by the wave nature of particles which explains electrons passing across small insulating gaps as matter waves

relativistic mass

the mass of a moving object as measured by an observer in the same frame of reference

STM microscope

scanning tunneling microscope - uses quantum tunneling of electrons between an electrode tip and atoms at the surface of a sample (1nm apart)

Stefan Boltzmann law

says that energy radiated per m^2 per s from a black body at temperature T is proportional to T^4

time dilation

time between 2 events appears longer for a system that is moving relative to the observer

TEM

transmission electron microscope -

UV catastrophe

The prediction of the Rayleigh-Jeans equation that radiated power per unit wavelength becomes infinite for short wavelengths, disproved by the fact that objects at ordinary temperatures do not emit intense UV and X-rays

wave theory

theory of light and other waves that explains reflection, refraction, diffraction and interference

wave-particle duality

the idea that EM energy and matter particles both exhibit wave-like and particle-like properties

Wien's displacement law

the wavelength of the peak emission intensity is inversely proportional to the absolute temperature (for hot objects)