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104 Cards in this Set
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Photoelectric Effect

the ejection of electrons from the surface of metals when light is incident on it. The escaping electrons are called photoelectrons


Photon

Electromagnetic waves of frequency f are emitted and absorbed in quanta of energy, E=hf, called photons.


Work function, Φ

The minimum amount of energy required to remove a free electron from the surface of a material. Φ = hf(0)


Ionisation Energy

The minimum amount of energy needed to remove an electron from an atom.


Photoelectric equation

A measure of the maximum kinetic energy of the electrons emitted as a result of the photoelectric effect. hf=Φ+Ek


Stopping Potential

The minimum frequency f(0) required to cause photoemission from a metal of work function hf(0). E=qV 

Binding Energy

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) 

Nuclear Fission

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


Nuclear Fusion

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.


Radioactivity

The spontaneous and random disintegration of an unstable nucleus into a more stable one by emitting alphaparticle, betaparticle and/ or gamma radiation.


Halflife

The expected time taken for half the number of radioactive nuclei present to decay in a sample. T1/2 = ln2/λ


Spontaneous Emission

A photon is emitted randomly and in any direction without any external stimulation


Stimulated Emission

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 

Population Inversion

When there are more atoms in the excited state than in the ground state.


Stimulated Absorption

When an atom at a lower energy level absorbs a photon and moves to a higher energy level.


Magnetic Flux density, B

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 

Electric Field

The electric force per unit charge.


Magnetic Flux Linkage

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 

Gravitational potential, Vg

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


Coulomb’s Law of Electrostatic Force

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)


Electric Field of Force

A region of space in which a charge experiences a force due to electrical effect of another charge.


Electric field strength

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 NC1)


Electric Potential, V

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 JC1). Energy potential = kQq/r (unit J) 

Gravitational potential energy

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.


Gravitational potential, Φ

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.


Gravitational field strength, g

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) 

Gravitational field

The gravitational field is a region where a gravitational force is experienced by another mass placed in it.


Newton’s Law of Gravitation

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) 

Diffraction

Diffraction is the spreading of waves when they pass through an opening or around an obstacle.


Coherence

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.


Path Difference

the difference between the distances travelled by two waves.


Interference

A resulting oscillation when a periodic driving force is applied to a system.


Principle of Superposition

When 2 or more waves meet, the resultant wave is equal to the vector sum of the individual displacements at that instant and position.


Root Mean Square

The rootmeansquare 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.


Electromotive force

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.


Potential Difference

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


Wavelength, λ

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 

Amplitude, A 
The magnitude of the maximum displacement of a particle from its equilibrium position.


Critical Damping

Critical damping is where the system, when displaced and released, returns to equilibrium, withing one complete oscillation.


Angular velocity

The rate of change of angular displacement per unit time. v=rω


Angular displacement 
The angle in radians through which a point of line has been rotated in a specific sense about an axis. s=rθ


Damping

The process whereby dissipative forces act to remove energy from an oscillating system, causing the amplitude of oscillation to decrease with time.


Simple Harmonic Motion

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.


Polarization

The process by which the oscillations of a wave are made to occur in one direction only.


Stationary waves

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 

Intensity

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.


Phase difference

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)


Frequency, f

Measured in Hz. The number of complete cycles of the oscillation each second. f=1/T 

Period, T

Time taken for one complete oscillation. 

Standing Wavelength

The wavelength of a standing wave is twice the distance between two nodes or between two antinodes. 

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 

Centripetal Acceleration 
The rate of change of tangential velocity. acentripetal= v(squared)/r 

Time taken to move once round a circular path: 
T=2πr/v 

Speed in orbit. (satellites) 
v(squared) = 4π(squared)R(squared)/T(squared) 

Energy in orbit. (satellites) 
Etotal= GMm/r + (1/2) GMm/r 

Refraction 
Bending of a wave caused by a change in its speed, as it passes from one material to another. 

Uniform Circular Motion

Refers to an object travelling at a constant speed on a circular path.


Angular Velocity

The rate of change of angular displacement per unit time.


Hooke’s Law

Within its limit of proportionality, the applied force, F, on a spring is directly proportional to its extension, x. F= kx


Systematic Errors

An error that causes the results to be always higher or always lower than the true value


Random Errors

An error that causes irregularities in the experiment, resulting in readings that are scattered about the true value.


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 

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. 

Faraday's Law 
The magnitude of the induced electromotive force is directly proportional to the rate of change of flux linkage. 

Snell's Law 
Refractive index going from material 1 to material 2. n = sin i/sin r = c1/c2 

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. 

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 

Power of a lens 
Measured in dioptres, where f is the focal length in metres. P=1/f 

Lens equation 
Curvature after lens is equal to the curvature before plus the curvature added. 1/v=1/u + 1/f 

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 

Angular frequency 
ω= 2πf 

Acceleration for SHM 
a= (2πf)(squared)s. At max acceleration replace s with A. 

Velocity for SHM 
Max velocity at the centre. vmax= (2πf)A 

Energy in a harmonic oscillator 
Etotal=1/2mv(squared) + 1/2 ks(squared) 

Progressive waves 
They propagate through space or through a substance. They transfer energy along the direction of travel. 

Nodes 
A position of minimum amplitude on a standing wave. 

Antinodes 
A position of maximum amplitude on a standing wave. 

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 

Harmonics (Closed end) 
First harmonic: f1 = v/4L Third harmonic: f3 = 3*v/4L Fifth harmonic: f5 = 5*v/4L 

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. 

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. 

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) 

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. 

Flemming's left hand rule 
thuMb  Motion First finger  Field seCond finger  Current 

Maxwell's right hand rule 
Finger of right hand curls with current; thumb shows direction of magnetic field. 

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 

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) 

Capacitance 
Charge stored per unit potential difference. C=Q/V. Unit; 1 Coulomb per volt  Farad (F) 

Time Constant (Capacitance) 
The time taken for the voltage or charge to drop 37% of its original value. 

Activity (Nuclear Physics) 
The number of radioactive decays per unit time. Unit = Becquerels. A= λN = A0e^λt 

Radioactivity equation 
N= N0e^λt N= no. remaining after time t N0= original number present t = time λ= decay constant [time constant = 1/λ] 

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. 

Isotopes 
Two nuclides (a nucleus with a distinct number of protons and neutrons) with thesame number of protons but different numbers of neutrons. 

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 

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 

Kirchoff's 2nd Law 
In any loop (path) around a circuit, the sum of the emfs = the sum of the pds. ΣE=ΣIR 

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. 

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 

Inductor [A.C.] 
A passive twoterminal 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) 

Henries (H) 
An inductor (L) has an inductance of 1H if a rate of change of current 1As1 through it produces an e.m.f. of 1 volt across it. 

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 

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 

Resonance 
Resonance occurs when a source of energy oscillates at the same frequency as the natural frequency of a structure. 

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) 