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104 Cards in this Set
- Front
- Back
Photoelectric Effect
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the ejection of electrons from the surface of metals when light is incident on it. The escaping electrons are called photoelectrons
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Photon
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Electromagnetic waves of frequency f are emitted and absorbed in quanta of energy, E=hf, called photons.
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Work function, Φ
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The minimum amount of energy required to remove a free electron from the surface of a material. Φ = hf(0)
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Ionisation Energy
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The minimum amount of energy needed to remove an electron from an atom.
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Photoelectric equation
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A measure of the maximum kinetic energy of the electrons emitted as a result of the photoelectric effect. hf=Φ+Ek
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Stopping Potential
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The minimum frequency f(0) required to cause photoemission from a metal of work function hf(0). E=qV |
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Binding Energy
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Nuclear binding energy is the energyrequired to split the nucleus of an atom into its component parts. These parts are called nucleons. E=mc(squared) |
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Nuclear Fission
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A nuclear process in which a heavy nucleus is split into lighter fragments of approximately equal mass, losing mass and releasing energy in the process. E.g Power plants
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Nuclear Fusion
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A nuclear process in which two or more nuclides of low mass number fuse into a nuclide of higher mass number, releasing energy in the process. E.g Fusion of hydrogen to helium in the sun.
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Radioactivity
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The spontaneous and random disintegration of an unstable nucleus into a more stable one by emitting alpha-particle, beta-particle and/ or gamma radiation.
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Half-life
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The expected time taken for half the number of radioactive nuclei present to decay in a sample. T1/2 = ln2/λ
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Spontaneous Emission
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A photon is emitted randomly and in any direction without any external stimulation
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Stimulated Emission
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An incoming photon, whose energy is exactly equal to the difference between two energy levels, induces the excited atom to fall into a lower energy level and releases a photon in the process. hf=Energy 2 - Energy 1 |
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Population Inversion
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When there are more atoms in the excited state than in the ground state.
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Stimulated Absorption
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When an atom at a lower energy level absorbs a photon and moves to a higher energy level.
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Magnetic Flux density, B
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The strength of a magnetic field. Defined as the force of one newton to act on a current of one ampere in a wire of length one metre which is perpendicular to the magnetic field. B=F/ILsinθ |
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Electric Field
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The electric force per unit charge.
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Magnetic Flux Linkage
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A coil of N turns of cross section A is placed in a magnetic field of flux density B with its axis along the field, has a flux linkage of Ф = N Ф = BAN |
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Gravitational potential, Vg
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The gravitational potential Vg, at a point in a gravitational field is defined as the work done per unit mass in bringing a small object from infinity to that point. Vg = -GM/r. Energy potential = -GMm/r
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Coulomb’s Law of Electrostatic Force
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The electrostatic force F between two point charges Q1 and Q2 is directly proportional to the product of the charges and inversely proportional to the square of the distance r between them. F=kQq/r(squared)
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Electric Field of Force
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A region of space in which a charge experiences a force due to electrical effect of another charge.
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Electric field strength
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The electric field strength E at a point P in an electric field is defined as the force experienced per unit +ve charge placed at that point. E=F/Q (unit NC-1)
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Electric Potential, V
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The electric potential V at a point in an electric field is defined as the work done per unit positive charge by an external agent to move a charge from infinity to that point. Ve = kQ/r (unit JC-1). Energy potential = kQq/r (unit J) |
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Gravitational potential energy
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The gravitational potential energy of a mass, m, placed at a point in the gravitational field is defined as the work done in bringing it from infinity to that point.
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Gravitational potential, Φ
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The gravitational potential, Φ, at a point in a gravitational field is defined as the work done per unit mass in bringing a test mass from infinity to that point.
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Gravitational field strength, g
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The gravitational field strength, g, at a point is the gravitational force per unit mass acting on a small mass at that point. g=F/m. g= -GM/r(squared) |
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Gravitational field
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The gravitational field is a region where a gravitational force is experienced by another mass placed in it.
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Newton’s Law of Gravitation
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Every particle of matter in the universe attracts every other particle with a force that is directly proportional to the product of the masses of the particles and inversely proportional to the square of the distance between them. F= - GMm/r(squared) |
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Diffraction
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Diffraction is the spreading of waves when they pass through an opening or around an obstacle.
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Coherence
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Two waves are coherent when the phase difference between them is constant. They should have the same frequency and wavelength and approx the same amplitude.
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Path Difference
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the difference between the distances travelled by two waves.
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Interference
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A resulting oscillation when a periodic driving force is applied to a system.
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Principle of Superposition
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When 2 or more waves meet, the resultant wave is equal to the vector sum of the individual displacements at that instant and position.
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Root Mean Square
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The root-mean-square of an alternating current (or voltage) is defined as that value of steady direct current (or voltage) which would dissipate energy at the same rate in a given resistance.
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Electromotive force
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E.m.f is defined as the energy converted from other forms into electrical energy by a source in driving a unit charge round a complete circuit.
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Potential Difference
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1 volt is the potential difference between two points in a circuit when 1 Joule of work is done moving 1 coulomb of charge between two points. p.d.=energy/charge
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Wavelength, λ
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The distance, measured in the direction of propagation of a wave, between two successive points in the wave that are characterized by the same phase of oscillation. v=f λ |
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Amplitude, A |
The magnitude of the maximum displacement of a particle from its equilibrium position.
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Critical Damping
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Critical damping is where the system, when displaced and released, returns to equilibrium, withing one complete oscillation.
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Angular velocity
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The rate of change of angular displacement per unit time. v=rω
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Angular displacement |
The angle in radians through which a point of line has been rotated in a specific sense about an axis. s=rθ
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Damping
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The process whereby dissipative forces act to remove energy from an oscillating system, causing the amplitude of oscillation to decrease with time.
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Simple Harmonic Motion
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An oscillatory motion in which the object’s acceleration is directly proportional to its displacement from equilibrium AND is always directed towards the centre of oscillation.
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Polarization
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The process by which the oscillations of a wave are made to occur in one direction only.
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Stationary waves
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They are the result of the superposition of two waves of similar amplitude, frequency and plane travelling in opposite directions. They do not transfer energy along the direction of travel |
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Intensity
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The intensity of a wave motion at a point is defined as the power per unit area incident normally to the surface at that point.
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Phase difference
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The fraction of one cycle by which one wave moves behind the other. For t=0 at equlibrium, s=Asin(2πft). For t=0 at max displacement (A) s=Acos(2πft)
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Frequency, f
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Measured in Hz. The number of complete cycles of the oscillation each second. f=1/T |
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Period, T
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Time taken for one complete oscillation. |
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Standing Wavelength
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The wavelength of a standing wave is twice the distance between two nodes or between two antinodes. |
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Centripetal Force |
A force which acts on a body moving in a circular path and is directed towards the centre around which the body is moving. Fcentripetal = mv(squared)/r |
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Centripetal Acceleration |
The rate of change of tangential velocity. acentripetal= v(squared)/r |
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Time taken to move once round a circular path: |
T=2πr/v |
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Speed in orbit. (satellites) |
v(squared) = 4π(squared)R(squared)/T(squared) |
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Energy in orbit. (satellites) |
Etotal= -GMm/r + (1/2) GMm/r |
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Refraction |
Bending of a wave caused by a change in its speed, as it passes from one material to another. |
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Uniform Circular Motion
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Refers to an object travelling at a constant speed on a circular path.
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Angular Velocity
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The rate of change of angular displacement per unit time.
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Hooke’s Law
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Within its limit of proportionality, the applied force, F, on a spring is directly proportional to its extension, x. F= -kx
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Systematic Errors
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An error that causes the results to be always higher or always lower than the true value
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Random Errors
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An error that causes irregularities in the experiment, resulting in readings that are scattered about the true value.
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Magnetic Flux |
The 'amount of field' i.e. The product of the uniform magnetic field times by the perpendicular area that it penetrates. Φm=BA |
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Lenz's Law |
If an induced e.m.f flows, its direction is always such that it will oppose the change which produced it. Obeys Newton's 3rd Law, the conservation of energy. |
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Faraday's Law |
The magnitude of the induced electromotive force is directly proportional to the rate of change of flux linkage. |
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Snell's Law |
Refractive index going from material 1 to material 2. n = sin i/sin r = c1/c2 |
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Focal point, F |
The focal point of a converging lens is the point where light from a very distant point object is brought to focus by the lens. |
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Focal length, f |
The focal length f of a thin lens is the distance from the centre of the lens to F, the focal point |
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Power of a lens |
Measured in dioptres, where f is the focal length in metres. P=1/f |
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Lens equation |
Curvature after lens is equal to the curvature before plus the curvature added. 1/v=1/u + 1/f |
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Linear magnification |
The ratio of the height or length of the image to the height or length of the object viewed directly. magnification = height of image/height of object. m=v/u |
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Angular frequency |
ω= 2πf |
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Acceleration for SHM |
a= -(2πf)(squared)s. At max acceleration replace s with A. |
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Velocity for SHM |
Max velocity at the centre. vmax= (2πf)A |
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Energy in a harmonic oscillator |
Etotal=1/2mv(squared) + 1/2 ks(squared) |
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Progressive waves |
They propagate through space or through a substance. They transfer energy along the direction of travel. |
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Nodes |
A position of minimum amplitude on a standing wave. |
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Antinodes |
A position of maximum amplitude on a standing wave. |
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Harmonics (Open end) |
First harmonic(fundamental): f1 = v/2L Second harmonic(1st overtone): f2 = 2*v/2L Third harmonic(2nd overtone): f3 = 3*v/2L |
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Harmonics (Closed end) |
First harmonic: f1 = v/4L Third harmonic: f3 = 3*v/4L Fifth harmonic: f5 = 5*v/4L |
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Huygens' wavelets |
The theory considers each point on a wavefront as a secondary emitter of wavelets. The wavelets from the points along a wavefront create a new wavefront, so that the wave propagates. |
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Phasors |
Phasors are used to represent amplitude and phase in a wave. A phasor is a rotating arrow used to represent a sinusoidally changing quantity. |
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Young's double slit experiment |
Calculate wavelength: λ = dx/L Intensity minima: dsinθ = nλ [Bright fringes] dsinθ = (n+1/2)λ [Dark fringes] (d, gap width; n is a positive integer) |
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Transverse waves |
A wave in which the motion of the medium is a right angles to the direction of the wave. e.g Light and EM waves. |
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Flemming's left hand rule |
thuMb - Motion First finger - Field seCond finger - Current |
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Maxwell's right hand rule |
Finger of right hand curls with current; thumb shows direction of magnetic field. |
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Force on a conductor in a magnetic field. |
When the conductor is placed at right angles to the magnetic field, a force is experienced by the conductor. F=BIL |
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Definitions of moving charges |
q=It. If the charge is moving with velocity v, then the distance it travels in time t is L=vt. F=Bqv (Bev for an electron) |
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Capacitance |
Charge stored per unit potential difference. C=Q/V. Unit; 1 Coulomb per volt - Farad (F) |
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Time Constant (Capacitance) |
The time taken for the voltage or charge to drop 37% of its original value. |
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Activity (Nuclear Physics) |
The number of radioactive decays per unit time. Unit = Becquerels. A= -λN = A0e^-λt |
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Radioactivity equation |
N= N0e^-λt N= no. remaining after time t N0= original number present t = time λ= decay constant [time constant = 1/λ] |
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Proton Number - Nucleon Number |
Proton Number, Z - The number of protons in a nucleus. Nucleon Number, A - The number of nucleons(protons + neutrons) in any nucleus. |
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Isotopes |
Two nuclides (a nucleus with a distinct number of protons and neutrons) with thesame number of protons but different numbers of neutrons. |
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Graphing P.D./Charge. Energy stored. |
V=E/Q Energy = p.d x charge (the area beneath the graph). Remember area of triangle: 1/2 (V0Q0) This is the energy stored in a capacitor |
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Kirchoff's 1st Law |
At any junction in a circuit, the sum of the currents arriving at the junction = the sum of the currents leaving the junction. The sum of the currents at a junction is zero. ΣI=0 |
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Kirchoff's 2nd Law |
In any loop (path) around a circuit, the sum of the emfs = the sum of the pds. ΣE=ΣIR |
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Alternating current |
An electric current that repeatedly reverses its direction, usually at a constant frequency. In 1 cycle, current/p.d reverses from its peak value in 1 direction to its peak value in the other and back again. |
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Root mean square (rms) [A.C.] |
The r.m.s. value of an a.c. supply is the steady d.c. which would convert electrical energy to thermal energy at the same rate in a given resistance. V=V0/root:2 (same for I) Pmean=Irms*Vrms |
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Inductor [A.C.] |
A passive two-terminal electrical component which resists changes in electric current passing through it. When a current flows through it it stores energy temporarily in a magnetic field. XL = 2πfL (ohms) |
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Henries (H) |
An inductor (L) has an inductance of 1H if a rate of change of current 1As-1 through it produces an e.m.f. of 1 volt across it. |
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Capacitor [A.C.] |
For a.c. circuits, the cell appears to be constantly charging due to the change in direction of the current. But the capacitor does offer opposition; this is called reactance. XC = 1/2πfC |
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Transformer [A.C.] |
Changes the peak voltage of an alternating potential difference. Rule: Vp/Vs=Np/Ns. N=number of turns on coil. V=p.d Assuming 100% efficiency, IpVp=IsVs |
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Resonance |
Resonance occurs when a source of energy oscillates at the same frequency as the natural frequency of a structure. |
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Electromotive force (e.m.f.) |
the energy provided by a cell or battery per coulomb of charge passing through it, it is measured in volts (V) |