All words Flashcards
work function of a metal
mimimum amount of energy needed by an electron to escape from a metal surfacce
X-rays
electromagnetic radiation of wavelength less than about 1nm. X-rays are emitted from an X-ray tube as a results of of fast-moving electrons from a heated filament as the cathode being stopped on impact with the metal anode. X-rays are ionising and the penetrate matter. Thick lead plates are needed to absorb a beam of X-rays.
yield point
point at which the stress in a wire suddenly drops when the wire is subjected to increasing strain
Young’s fringes
parallel bright and dark fringes observed when light from a narrow slit passes through two closely spaced slits
Young modulus
tensile stress/strain (assuming the limit of proportionality has not been exceeded). The unit of the Young modulus is the pascal (Pa) which is equal to 1 N/m2
Potential Gradient
at a point in a field is the change of potential per unit change of distance along the field line at that point. The Potential Gradient= - the field strength at any point.
Power
Rate of transfer of energy= energy transferred/time taken
Pressure
The force per unit area that a gas or a liquid or a solid at rest exerts normally on (i.e. at right angles to) a surface. Pressure is measured in pascals (Pa), where 1 Pa=1 Nm-2
Pressure law
for a fixed mass of an ideal gas at constant volume, its pressure is directly proportional to its absolute temperature
Principle of conservation of momentum
when two or more bodies interact, the total momentum is unchanged, providing no external forces act on the bodies.
Principle of conservation of energy
in any change, the total amount of energy after the change is always equal to the total amount of energy before the change
Principle of moments
for an object in equilibrium, the sum of the clockwise moments about any point= the sum of the anticlockwise moments about that point
Progressive waves
waves which travel through a substance or through space if electromagnetic
Projectile
a projected object in motion acted on only by the force of gravity
Proton
a particle that has equal and opposite charge to an electron and has a rest mass 1.673 x10-27 kg which is about 1836 times that of an electron. Protons are in every atomic nucleus. The nucleus of hydrogen 1H1 is a single proton. The proton is the only stable baryon.
Quark
protons and neutrons and other hadrons consist of quarks. There are six types of quarks: the up quark, the down quark, the strange quark, the charmed quark, the top quark, and the bottom quark.
Quark model (or standard model)
a quark can join with an antiquark to form a meson or with two other quarks to form a baryon. An antiquark can join with two other antiquarks to form an anti baryon.
Radial Field
a field in which the field lines are straight and converge or diverge as if from a single point
Radian
1 Radian= 360/2π degrees , 2π Radians= 360 degrees
Reactor core
the fuel rods and the control rods together with the moderator substance are in a steel vessel through which the coolant (which is also the moderator in ‘pressurised water reactor’) is pumped.
Refraction
change of direction of a wave when it crosses a boundary where its speed changes
Refractive index
(Speed of light in free space)/(speed of light in the substance)
Relative Permittivity
ratio of the charge stored by a parallel- plate capacitor which dielectric filling the space between its plates to the charge stored without the dielectric for the same pd
Renewable energy
energy from a source that is continually renewed. Examples include hydroelectricity, tidal power, geothermal power, solar power, wave power, and wind power
Resistance
pd/current
Resistivity
Resistance per unit length x area of cross section
Resonance
The amplitude of vibration of an oscillating system subjected to a periodic force is largest when the periodic force has the same frequency as the resonant frequency of the system. for a lightly damped system, the frequency of the periodic force = natural frequency of the oscillating system. At resonance, the system vibrates such that its velocity is in phase with the periodic force.
Resonant frequency
the frequency of an oscillating system in resonance
Rest energy
energy due to rest mass, m , equal to mc2, where c is the speed of light in free space
Root mean square speed
square root of the mean value of the square of the molecular speeds of the molecules of a gas
Rutherford’s α- particle scattering experiment
demonstrated that every atom contains a positively charged nucleus which is much smaller than the atom and where all the positive charge and most of the mass of the atom is located
Satellite
A small object in orbit round a larger object
Satellite motion
for a satellite moving at speed vin a circular orbit of radius r round a planet, its centripetal acceleration, g= (v^2)/r
Motor Effect
The force on a current-carrying conductor due to a magnetic field
Muon
A lepton which is negatively charged and has a greater rest mass than the electron
Natural Frequency
The frequency of free oscillations of an oscillating system
Negative Temperature coefficient
The resistance of a semiconductor decreases when its temperature is increased
Neutron
An uncharged particle that has a rest mass of 1.674*10^-27 kg. Neutrons are in every atomic nucleus except that of hydrogen
Neutrino
Uncharged lepton with a very low rest mass compared with the electron
Neutrino Types
There are 3 types of neutrinos: the electron neutrino, the muon neutrino, and the tau neutrino
Newton’s Law of Gravitation
The gravitational force F between two point masses m1 and m2 at distance r apart is given by : F = Gm1m2/r^2
Newton’s First Law of Motion
An object continues at rest or in uniform motion unless it is acted on by a resultant force
Newton’s Second Law of Motion
The rate of change of momentum of an object is proportional to the resultant force on it (resultant force = change in momentum/change in time)
Newton’s Third Law of Motion
When two objects interact, they exert equal and opposite forces on one another
Node
Fixed point in a stationary wave pattern where the amplitude is zero
Nuclear Fission
The splitting of a Uranium-235 nucleus or Plutonium-235 nucleus into two approximately equal fragments. Induced fission is caused by an incoming neutron colliding with the nucleus
Nuclear Fusion
The fusing together of two light nuclei to form a heavier nucleus
Nucleon
A neutron or a proton in the nucleus
Nucleon Number A
The number of neutrons and protons in a nucleus, also referred to as mass number
Nucleus
The relatively small part of an atom where all the atom’s positive charge and most of its mass is concentrated
Ohm’s Law
The pd across a metallic conductor is proportional to the current as long as the physical conditions do not change
Optical Fibre
A thin flexible transparent fibre used to carry light pulses from one end to another
Pair Production
When a gamma photon changes into a particle and an antiparticle
Pascal
Unit of pressure or stress equal to 1 Nm^-2
Path Difference
The difference in distances from two coherent sources to an interference fringe
Period of a wave
Time for one complete cycle of a wave to pass a point
Periodic Force
A force that varies regularly in magnitude with a definite time period
Permittivity of free space
The charge per unit area in coulombs per square metre on oppositely charged parallel plates in a vacuum when the electric field strength between the plates is 1 volt per metre
Phase Difference
In radians, for two objects oscillating with the same time period the phase difference = 2pichange in time/Time period, where change in time is the time between successive instants when the two objects are at maximum displacement in the same direction
Photoelectric Effect
Emission of electrons from a metal surface when the surface is illuminated by a light of frequency greater than a minimum value known as the threshold frequency
Photon
Electromagnetic radiation consists of photons. Each photon is a wave packet of electromagnetic radiation. The energy of a photon is E = hf where h is Planck’s constant and f is the frequency of the radiation
Pion
A meson that consists of an up or down quark and an up or down antiquark
Plane-polarised waves
Transverse waves that vibrate in one plane only
Plastic Deformation
Deformation of a solid beyond its plastic limit
Positive Temperature Coefficient
The resistance of a metal increases when its temperature is increased
Positron
A particle of antimatter that is the antiparticle of the electron
Potential Difference
The work done or energy transfer per unit charge between two points when charge moves from one point to the other
Potential Divider
Two or more resistors in series connected to a source of pd
Potential Energy
The energy of an object due to its position
accepted value
value of the most accurate measurement available, sometime referred to as the ‘true value’
accuracy
The closeness of a measurement to the true value (if known)
dependent variable
a physical quantity whose value depends on the value of another physical variable
error bar
representation of an uncertainty on a graph
random errors
errors vary randomly with no recognisable pattern or trend or bias
systematic errors
differ systematically and show a pattern or trend or bias
independent variable
physical quantities whose values are selected or controlled by the experimenter
linearity
an instrument that gives readings that are directly proportional to the magnitude of the quantity being measured
mean value of a set of readings
sum of the readings divided by the number of readings
percentage uncertainty
=uncertainty/mean value x 100%
precision of a measurement
the degree of exactness of a measurement, usually expressed as the uncertainty off the readings used to obtain the measurement
precision of an instrument
the smallest non-zero reading that can be measured using the instrument, also sometimes referred to as the instrument sensitivity or resolution
range of a set of readings
the difference between the largest and smallest reading
range of an instrument
the difference between the minimum and maximum reading that can be obtained using the instrument
reliability
an experiment or measurement is reliable if a consistent value is obtained each time it is repeated under identical conditions. The reliability of an experiment is increased if random and systematic errors have been considered and eliminated and, where appropriate, a more precise best fit line has been obtained.
repeatable
an experiment or measurement that gives the same results when it is repeated by the original experimenter using the same method and equipment
reproducable
an experiment or measurement that gives the same results when it is repeated by another person or by using different equipment or techniques.
sensitivity of an instrument
output response per unit input quantity
uncertainty of a measurement
half the range of the readings used to obtain the measurement
valid measurement
measurements that give the required information by an acceptable method
zero error of an instrument
a systematic error due to a non-zero reading when the quantity to be measured is zero
Time constant
The time taken for a quantity that decreases exponentially to decrease to 0.37 of its initial value. For the discharge of a capacitor through a fixed resistor, the time constant = resistance x capacitance.
Time period or period
Time taken for one complete cycle of oscillations.
Total internal reflection
A light ray travelling in a substance is totally internally reflected at a boundary with a substance of lower refractive index, if the angle of incidence is greater than a certain value known as the critical angle.
Transformer
Converts the amplitude of an alternating pd to a different value. It consists of two insulated coils, the primary coil and the secondary coil, wound round a soft iron laminated core; step-down transformer: a transformer in which the rms pd across the secondary coil is less than the rms pd applied to the primary coil; step-up transformer: a transformer in which the rms pd across the secondary coil is greater than the rms pd applied to the primary coil.
Transformer rule
The ratio of the secondary voltage to the primary voltage is equal to the ratio of the number of secondary turns to the number of primary turns.
Transformer efficiency
For an ideal transformer (i.e., one that is 100% efficient), the output power (= secondary voltage x secondary current) = the input power (=primary voltage x primary current). Transformer inefficiency is due to: resistance heating of a current in each coil; the heating effect of eddy currents (i.e., unwanted induced currents) in the core; and heating caused by repeated magnetisation and demagnetisation of the core.
Transverse waves
Waves with a direction of vibration perpendicular to the direction of propagation of the waves.
Types of light spectra
Continuous spectrum - continuous range of colours corresponding to a continuous range of wavelengths,
Line emission spectrum - characteristic coloured vertical lines, each corresponding to a certain wavelength,
Line absorption spectrum - dark vertical lines against a continuous range of colours, each line corresponding to a certain wavelength.
Ultimate tensile stress
Tensile stress needed to break a solid material.
Uniform circular motion
Motion of an object moving at constant speed along a circular path.
Uniform field
A region where the field strength is the same in magnitude and direction at every point in the field.
- The electric field between two oppositely charged parallel plates is uniform. The electric field strength E = V/d, where V is the pd between the plates and d is the perpendicular distance between the plates.
- The gravitational field of the Earth is uniform over a region which is small compared to the scale of the Earth.
- The magnetic field inside a solenoid carrying a constant current along and near the axis.
Universal constant of gravitation
See gravitational constant.
Useful energy
Energy transferred to where it is wanted when it is wanted.
Vector
A physical quantity with magnitude and direction.
Velocity
Change of displacement per unit time.
Virtual photon
Carrier of the electromagnetic force; a photon exchanged between two charged particles when they interact.
W boson
Carrier of the weak nuclear force; W bosons have non-zero rest mass and may be positive or negative.
Wave-particle duality
- Matter particles have a wave-like nature, for example, electrons directed at a thin crystal are diffracted by the crystal, and particle-like behaviour, such as electrons in a beam deflected by a magnetic field. See de Broglie wavelength.
- Photons have a particle-like nature, as shown in the photoelectric effect, as well as a wave-like nature as shown in diffraction experiments.
Wavefronts
Lines of constant phase (e.g., wavecrests).
Wavelength
The least distance between two adjacent vibrating particles with the same displacement and velocity at the same time (e.g., distance between two adjacent wave peaks).
Weak interaction
Interaction between two leptons.
Weak nuclear force
Force responsible for beta decay.
Weight
The force of gravity acting on an object.
Work done
Work is energy transferred by means of a force. Work = force x distance moved in the direction of the force. The work done W by a force F when its point of application moves through displacement s at angle (theta) to the direction of the force is given by W = Fs cos (theta).
