IGCSE Physics Definitions Flashcards
In order of: 1. Forces and Motion 2. Electricity 3. Waves 4. Energy and Thermal 5. Solids, Liquids and Gases 6. Electromagnetism 7. Atomic Physics 8. Astrophysics
Forces and Motion
Scalar
A quantity that has a magnitude
Vector
A quantity that has magnitude and direction
The moment (or torque) of a force
force * the perpendicular distance from the point to the line of action of the force, ie moment = F x d, UNIT: Nm
the principle of motions
for a system to be in equilibrium, sum of anticlockwise moments about a point = sum of clockwise moments about the same point
centre of gravity
the single point within a body at which the entire weight of the body is considered to act
displacement
the displacement of a point B from a point A is the shortest distance from A to B, together with the shortest distance. unit: m
average speed
average speed = total distance travelled / total time taken
instantaneous speed
rate of change of distance. unit: m/s
average velocity
average velocity = total displacement / total time taken. unit: m/s
velocity
the velocity of a body is the rate of change of displacement. unit: m/s
average acceleration
average acceleration = change in velocity / time taken. unit: m/s^2
momentum
the momentum of an object is its mass multiplied by its velocity. (p = mv). it is a vector. unit: kg m/s
mass
a measure of the amount of substance (matter) in an object
gravitational field strength (g)
the force experienced per unit mass by a mass placed in the field
weight
the force that acts upon an object due to its position in a gravitational field
resultant force
when the forces acting on an object are unbalanced, causing the object to accelerate
newton’s 1st law of motion
an object continues in a state of uniform motion in a straight line, or remains at rest, unless acted upon by a resultant force
newton’s 2nd law of motion
the rate of change of momentum of an object is proportional to the resultant force acting on it, and takes place in the direction of that force
newton’s 3rd law of motion
if an object A exerts a force on a second object B then B must exert a force which is equal in magnitude but opposite in direction on A
elastic collision
a collision in which there is no loss of kinetic energy
inelastic collision
a collision in which kinetic energy is lost
hooke’s law
the extension of an object such as a wire or spring is proportional to the stretching force, provided the extension is not too large. (F = kx)
friction
a force that acts between two surfaces that resists motion between the surfaces
terminal velocity
the terminal velocity is the constant, maximum velocity of an object when the resistive forces on it are equal and opposite to the accelerating forces (eg pull of gravity)
extension
extension = stretched length - original length
spring constant
the spring constant (k) is the force per unit extension. unit: N/m
efficiency
efficiency = useful output work or energy / input work or energy
Electricity
alternating current
an electric current that periodically reverses in direction in the circuit
electric current, I
this is the rate of flow of electric charge. I = Qt. unit: A
potential difference (p.d.), V
the p.d. between two points is the energy converted from electrical potential energy to some other form per coulomb of charge flowing from one point to the other. unit: vols (V) [= J/C]
Ohm’s law
the current flowing through a metal wire at constant temperature is proportional to the p.d across it
electrical resistance, R
the resistance of a conductor is the p.d. (V) placed across it divided by the resulting current (I) through it. R = V / I
Waves
angle of incidence
the angle between an incident ray and the normal to the surface
angle of refraction
the angle between a refracted ray and the normal to the surface
normal
the line that is perpendicular to a surface used in reflection and refraction
law of reflection
the angle of incidence equals the angle of reflection
critical angle
the angle of incidence which gives an angle of refraction at 90 degrees to the normal of the surface
period T
period for an oscillating body is the time taken for one complete cycle, period = 1/T
amplitude
the amplitude is defined as the maximum displacement of any particle (or wave) from its equilibrium position
wavelength
the wavelength of a progressive wave is the minimum distance between two points on the wave oscillating in phase. unit: m
frequency
the frequency of a wave is the number of cycles of a wave per unit time (seconds). unit: Hz
wave speed
the speed of a wave is the distance that the wave profile moves per unit time
intensity of a wave
energy per second passing normally through a given area
transverse wave
a transverse wave is one where the particle oscillations are at 90 degrees (right angle) to the direction of travel (or propagation) of the wave
longitudinal wave
a longitudinal wave is one where the particle oscillations are in line with (parallel to) the direction of travel (or propagation) of the wave
Snell’s law
at the boundary between any two given materials, the ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant. c = sin i / sin r
refraction
the change in direction of a wave due to a change in wavespeed as it passes across a boundary between two different media
refractive index
the ratio between the speed of light in a vacuum to the speed of light in the medium
Energy and Thermal
energy
the energy of a body or system is the amount of work it can do. unit: joule (J)
kinetic energy
the energy possessed by a body due to its motion
potential energy
the energy stored within an object due to its position, state or shape
work
work done by a force is the product of the magnitude of the force and the distance moved in the direction of the force. unit: joule (J) [= Nm]
power
this is the work done per second, or energy converted or transferred per second. unit: watt (W) [= J/s]
gravitational potential energy
this is the energy possessed by virtue of position. gravitational PE = mgh
law of conservation of energy
energy cannot be created or destroyed, only transformed from one form to another
conduction
the process by which thermal energy is transmitted through materials from one vibrating particle to another
convection
the process by which thermal energy is transmitted from one place to another by the movement of convection currents due to differences in density
radiation
the transfer of energy by electromagnetic waves.
Solids, liquids and gases
density
the mass per unit volume of an object, density = mass / volume
Boyle’s law
for a fixed mass of gas at constant temperature, the pressure varies inversely as the volume. (p = k/V)
ideal gas
an ideal gas strictly obeys the gas laws at all pressures, temperatures and volumes
specific heat capacity, c
the heat energy required, per kilogram, per degree celsius or kelvin, to raise the temperature of a substance. unit: J/kgK or J/kg{*}C
Electricmagnetism
magnetic field lines
lines showing the strength of a magnetic field, from north to south
hard/soft magnetic material
difficult/easy to magnetise and demagnetise
the motor effect
a current flowing perpendicular to a magnetic field and causing a force (using Fleming’s left hand rule)
induction
when a conductor is subjected to a changing magnetic field a potential difference is created across its ends
Atomic Physics
nucleon
protons and neutrons have similar masses. they are both classed as nucleons as they reside within the nucleus
atomic mass number, A
the atomic mass number of an atom is the number of nucleons (number of protons + number of neutrons) in its nucleus
atomic number, Z
the atomic number of an atom is the number of protons in its nucleus. [this determines the chemical element which the atom represents]
isotope
isotopes of an element are atoms with the same number of protons, but different numbers of neutrons in their nuclei. they have the same atomic number Z but different mass number A
radioisotope
radioisotope are simply isotopes which are radioactive
alpha radiation
a stream of helium nuclei, 2 protons and 2 neutrons
beta radiation
a stream of electrons
gamma radiation
short wavelength electromagnetic radiation (shorter than x-rays)
half life
the average time taken for the number of radioactive nuclei N (or the activity A) to reduce to one half of the initial value. unit: s
activity, A
the rate of decay (number of disintegrations per second) of a sample of radioactive nuclei. unit: becquerels, Bq (= /s)
nuclear fission
the process in which a large nucleus is split to release energy
nuclear fusion
the process in which two small nuclei are joined together having overcome their electrostatic repulsion to release energy
Astrophysics
universe
the universe is a large collection of billions of galaxies
galaxy
a large collection of billions of stars
redshift
the increase in the wavelength of received light from distant galaxies which gives evidence supporting an expanding universe (big bang theory)
doppler effect
the change in the apparent frequency of a wave due to relative motion between the source of the wave and the observer
cosmic microwave background radiation (CMB)
microwave radiation detected coming from all directions which is theorised to be left over from the Big Bang
