S

satellite - any body, natural or man-made that orbits a planet
saturated vapour - a vapour in equilibrium with excess of its liquid
Saturn - sixth planet from the Sun. Superb ring system.
saw tooth - a wave with a shape like the teeth of a saw
scalar - quantity with size (magnitude) only (e.g. mass, volume, distance)
scaler - instrument used for timing or measuring count rates
scanning - motion of the electron beam across a TV screen
schlieren effect - shadows produced by hot moving fluids due to the change in their refractive index
schmidt - telescope/camera with spherical main mirror and shaped correcting plate
scintillation - giving out flashes of light when a particle hits it
search coil - a small coil used to investigate electric or magnetic fields
searle's bar - apparatus used for measuring the conductivity of a good conductor
seismometer - device for measuring and detecting earthquakes
secondary cell - electric cell that must be charged before use
secondary colours - yellow, magenta and cyan (in light)
self induction - a changing current within a circuit inducing a back e.m.f. within it
semicircular block - a half circular block of glass or plastic used in optics experiments
semiconductor - material with few free electrons at room temperature
semitone - smallest interval of pitch between two tones in western music
series - connected in line one after the other, as in series resistors
sextant - instrument for measuring the angle of the Sun or a star above the horizon.
shear stress - a stress acting across the length of an object that deforms it in this direction
S.H.M - simple harmonic motion, acceleration proportional to negative of displacement
siemens - unit of electrical conductance
SI units - internationally agreed set of units (metre, kg, second, amp etc.)
short circuit - a defect in a circuit that allows current to bypass the load, direct connection
shunt - one circuit connected to another in parallel
sidereal - to do with the stars
sidereal day - the length of day as measured by the stars, 3m 56 s less than the solar day
sign convention - rule about the sign of lengths in optical equations e.g. 'real is positive'
silicon - non- metallic semiconductor
simultaneous - occurring at the same time
sine - ratio of the opposite side to the hypotenuse in a right angled triangle
sine wave - a wave with displacement varying with the sine of an angle
singularity - matter with zero volume and infinite density – outside normal laws of Physics!
Sirius - brightest star visible from the Northern Hemisphere
sling shot - the acceleration of a space probe due to gravity assist
slip ring - part of an electric motor or dynamo
smoke box - a box with one transparent side that is filled with smoke and used to view light rays
snell's law - sin i/sin r = constant (the refractive index)
soft - magnetic material that is easy to magnetise and demagnetise e.g. soft iron
solar - to do with the Sun
solar cell - a device that converts light energy (e.g. from the Sun) to electrical energy
solar constant - solar energy falling on 1 m² normal to the direction per sec. (1353 W at Earth)
solar day - the time between successive transits of the sun across the meridian
solar eclipse - the Moon moves between the Sun and Earth; Sun's light to part of Earth is cut off
solar flare - huge curved jet of 'flaming' gas ejected from the surface of the Sun
solar sail - a very large but light sail designed to power spacecraft by reflecting sunlight
solar system - the Sun and all objects orbiting it (e.g. planets, comets, asteroids)
solar wind - a flow of particles (charged and uncharged) from the Sun
solenoid - a long, straight coil of wire
solute - substance dissolved in a pure liquid is called the solute
sonar - method of underwater distance measurement using reflected sound pulses
sonic boom - audible shock wave heard as a supersonic plane passes overhead
sonometer - a piece of apparatus used to study vibrating strings
source - origin of, as in radioactive (source), source of sound etc.
spark chamber - a device for detecting charged particles by the ionisation they produce
specific - referring to unit mass as in specific heat capacity and specific latent heat
specific charge - charge to mass ratio (as in e/m for an electron)
specific heat - the heat energy required to raise the temperature of 1 kg of material by 1 ^oC
specific gravity - the density of a materials based on the scale where the density of water is 1.
specular - type of reflection where the angles between rays in the beam is unchanged
spectral class - of stars, OBAFGKNRNS, classification of stars by their spectrum
spectroscope - instrument for splitting light from a source into its various colours (wavelengths)
spectrum - a separation of the colours of white light (or other distribution of wavelengths)
sphere - ball, globe
spherical - round, like a sphere
spherical aberration - defect of large spherical mirrors, focus not at a point
spin - quantum property of fundamental particles. (e.g. electron spin is ½ )
spring balance - instrument for measuring mass (or force) using the entension of a spring
square wave - a wave form with a shape like a series of squares
stable - do not decay, as in 'stable isotopes' – ones that do not decay
stable - balanced
stability - how stable an object is
standard form - a method of writing numbers as powers of ten, e.g. 5400 = 5.4x10³, 0.03 = 3x10^-2
standing wave - a wave where the amplitude is constant at a given point.
stationary wave - same as a standing wave
star - celestial body that emits energy due to nuclear fusion. The Sun is an average star.
static - at rest, still, not moving
stationary - at rest, still, not moving
stator - static part of an electric motor, generator or dynamo
Stefan-Boltzmann Law - for a black body, Energy output = s[T⁴ – T_o⁴]
steradian - a solid angle. Angle subtended by unit area at unit distance from a point, total 4p.
stereoscopic - 3D
stereoscopic vision - 3D vision due to two eyes
stop - device for cutting down the aperture of an optical instrument. Stopping down
strangeness - quantum number applied to members of a group of strange particles
strange particle - e.g. K, L and S discovered in the 1950s. Produced in pairs. Unusual properties.
stratosphere - region in the Earth's atmosphere between altitudes of about 8 km and 150 km
steady state theory - a theory of the Universe where matter is continually being created
stress - force/area
stroboscope - an instrument that can make moving objects appear to slow down or stop
strong force - in the nucleus, the force that holds the particles in the nucleus together
strain - change of shape or volume of a body due to a stress
strontium 90 - beta emitting radioisotope used in many school radioactivity kits
sublimation - turning directly from a solid to a gas. e.g. carbon dioxide
successive - one after the other, as in 'successive collisions'
Sun - the nearest star. Centre of our solar system. Surface temperature 6000 ^oC
sunspot - dark regions on the Sun's surface. Temperature 2000 ^oC lower than the rest
sunspot cycle - eleven year period between successive sunspot maxima
superconductor - material with effectively zero resistance
supergiants - stars with diameters many hundreds of times that of the Sun e.g. Betelguese
superior planets - those outside the orbit of Earth. Mars, Jupiter, Saturn, Uranus, Neptune, Pluto
supernova - a star that has exploded expelling all its material and energy 'in one go'
supersonic - faster than sound
surface tension - a force in the surface of a liquid making it act like an elastic skin
surge - a sudden increase in the voltage of an electrical supply
surplus - extra, additional, as in 'surplus energy'
S.V.P - saturated vapour pressure – the pressure in a saturated vapour
S-wave - a transverse mechanical vibration in the Earth's crust - secondary, shake
synchronous - two a.c signals or oscillations that are exactly in phase and remain in phase
synchronous - satellite, one that rotates with the same angular speed as the Earth
synchrotron - one form of device for accelerating charged particles to a high energy
systematic error - an error due to faulty apparatus