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30 terms

tesla

SI unit for magnetic flux density; equivalent to 1 newton per ampere per metre

weber

SI unit for magnetic flux

farad

coulomb per volt

parsec

distance that gives a parallax angle of 1 arcsecond

electric field strength

force per unit positive charge

magnetic flux

magnetic flux density x area (perpendicular to field direction)

magnetic flux linkage

magnetic flux x the number of turns

capacitance

charge per unit potential difference

time constant of a circuit

time taken for current/charge/voltage of a discharging capacitor to fall to 37% of its original value (equal to the product of capacitance and resistance

proton number

number of protons in the nucleus of an atom (a.k.a. atomic number)

nucleon number

number of neutrons and protons in the nucleus of an atom (a.k.a. mass number)

activity

the rate of decay of nuclei in a radioactive sample

decay constant

probability of a decay of a nucleus per unit time

half life

the mean time taken for half the number of active nuclei in a radioactive sample to decay

binding energy

minimum energy to separate protons and neutrons of a nucleus

intensity

power per unit cross-sectional area

Faraday's law of electromagnetic induction

induced e.m.f. is proportional to the rate of change of magnetic flux

Lenz's law

the induced current or e.m.f. is in a direction so as to produce effects which oppose the change producing it

isotope

a version of an element with a different number of neutrons (but the same number of protons and electrons)

Doppler effect

the change in the frequency and wavelength of a wave caused by the relative movement between source and detector

piezoelectric effect

application of a p.d. across a crystal causes a vibration

Compton effect

x-ray photon interacts with electron; the scattered photon has a longer wavelength and the electron is ejected

Olber's paradox

if Universe is static and infinite, the night sky should be uniformly bright because every line of sight would end on a star

Hubble's law

the speed of recession of a galaxy is proportional to its distance

cosmological principle

universe has the same large-scale structure when observed from any point (homogenous, isotropic and the laws of physics are universal

3K microwave background radiation

gamma radiation released during the Big Bang has stretched as the Universe expanded, causing it to become microwave with an energy equivalent to a temperature of 3K

critical density

the density for which the universe will expand towards a finite limit (resulting in a flat universe)

open universe

universe will expand forever

flat universe

universe will expand towards a finite limit

closed universe

universe will contract (to a big crunch)