# Shared Flashcard Set

## Details

OCR Unit 2 AS Physics
Definitions and Questions
131
Physics
Not Applicable
06/01/2011

Term
 Conservation of Charge
Definition
 Physical law stating charge is conserved in all interactions; it cannot be created or destroyed.
Term
 Conventional current
Definition
 A model used to describe the movement of charge in a circuit. Conventional current travels from + to -.
Term
 Components
Definition
 Parts of an electric circuit.
Term
 Conductor
Definition
 A material with a high number density of conduction electrons, and therefore a low resistance.
Term
 Coulomb
Definition
 Unit of electric charge. 1C = 1A x 1s
Term
 Absorption spectrum
Definition
 A spectrum of dark lines across the pattern of spectral colors produced when light passes though a gas and the gas absorbs certain frequencies depending on the elements in the gas.
Term
 Ammeter
Definition
 A device used to measure electric current, connected in series with components.
Term
 Progressive wave
Definition
 Is where energy is carried from one place to another.
Term
 Stationary wave/Standing wave
Definition
 Is where energy is stored rather than transmitted.
Term
 Node
Definition
 Points in a stationary wave at which there is no displacement of the particles at any time.
Term
 Anti-node
Definition
 The point on a stationary wave where the displacement of the particles varies by the maximum amount.
Term
 Internal resistance
Definition
 The resistance of a battery or cell, measure in ohms.
Term
 I-V characteristics
Definition
 A graph to show how the electric current through a component varies with the P.D across it.
Term
 Kilowatt-hour
Definition
 An unit of energy used by electricity companies when charging for electricity.
Term
 Interference
Definition
 The addition of two or more waves that results in a new wave pattern.
Term
 Coherence
Definition
 Two waves with a constant phase relationship.
Term
 Drift velocity
Definition
 The average velocity of an electron as it travels through a wire due to P.D.
Term
 Resistivity
Definition
 The ratio of the product of resistance and cross-sectional area of a component and its length.
Term
 Gamma rays
Definition
 A form of electromagnetic wave with wavelengths between (10^-6) to (10^-9)m.
Term
 Harmonics
Definition
 Whole number multiples of the fundamental frequency of a stationary wave.
Term
 Quantum
Definition
 A discrete, indivisable quantity.
Term
Definition
 Unit of angle or phas difference. One radian is the angle subtented at the centre of a circle by an arc of circumference that is equal in length to the radius of the circle.
Term
 Semiconductor
Definition
 A material with a smaller number density of conduction electrons than a conductor, therefor a higher resistance.
Term
 Series circuit
Definition
 A type of circuit where the components are connected end to end and therefore provide only one path for the electric current.
Term
 Wave
Definition
 A series of vibrations that transfer energy from one place to another.
Term
 Wavelength
Definition
 The smallest difference between one point on a wave and the identical point ofn the next peak. Measured in metres.
Term
 Wave-particle duality
Definition
 The theory that states all objects can exhibit both wave and particle properties.
Term
 Work function energy
Definition
 The minimum energy required to release an electron from a material, measured in joules.
Term
 Young's double slit
Definition
 An experiment to demonstarate the wave nature of light via superposition and interference.
Term
 Parallel circuit
Definition
 A type of circuit where the components are connected in two or more branches and therefore provide more than one path for the electric current.
Term
 Photocell
Definition
 A component that reduces it resistance when light shines on it due to photoelectric emission of electrons.
Term
 Spectrum
Definition
 A collection of waves with a range or frequencies, for example; the visible spectrum.
Term
 Spectral line
Definition
 A line relating to a specific frequency either missing from an absorption spectrum or present in an emission spectrum.
Term
 Thermistor
Definition
 A component that changes it resistance depending on temperature. An NTC thermistor's resistance reduces as the temperatre increases.
Term
 Electron volt
Definition
 One electron volt is the energy charge of an electron when it moves through a P.D of one volt. Its value is 1.60x10^-19
Term
 Emission spectrum
Definition
 A pattern of colors of light, each color having a specific wavelength.
Term
 Energy level
Definition
 One of the specific energies an electron can have when in an atom.
Term
 Dynamo
Definition
 A device that converts kinetic energy into electrical energy.
Term
 Electromagnetic wave
Definition
 A self propagating transverse wave that does not require a medium to travel through.
Term
 Electrolyte
Definition
 A fluid that contains ions that are free to move and hence conduct electricity.
Term
 Light dependant resistor
Definition
 A component that changes its resistance with changes in the light intensity. (Dark conditions = High resistance)
Term
 Light emitting diode
Definition
 A component that allows electric current to pass through it in one direction only and that emits light when a P.D is applied across it.
Term
 Infra-red
Definition
 A form of electromagnetic wave with wavelengths of (7.4x10^-7) and (10^-3)m.
Term
 Insulator
Definition
 A material with a very small number density of conduction electrons, therefore leading to a very high resistance.
Term
 Intensity
Definition
 The energy incident per square metre of a surface per second. 1Wm^-2
Term
 Monochromatic light
Definition
 Light waves with a single frequency or wavelength.
Term
 Ohm's law
Definition
 The electric current through a conductor is proportional to the P.D across it, provided that the physical conditions reain the same.
Term
 Ohm
Definition
 Unit of resistance 1ohm = 1VA^-1
Term
 Fundamental frequency
Definition
 The frequency in a harmonic series where a stationary wave forms.
Term
 Fuse
Definition
 An electrical component designed to heat up, melt and break the circuit when a specific amount of electric current passes through it. It is used as a safety device.
Term
 Electromotive force
Definition
 The electrical energy transferred per unit charge when one form of energy is converted into electical energy. easured in volts.
Term
 Electron
Definition
 Negatively charged sub-atomic particle. Conduction electrions travel around a circuit to create an electric current.
Term
 Diffraction
Definition
 When a wave spreads out after passing around an obsticle or through a gap.
Term
 De broglie equation
Definition
 An equation expressing the wavelength of a particle as a ratio of planck's constant and the particle's momentum.
Term
 Electron diffraction
Definition
 The process of diffracting an electron through a gap (usually between atoms in a crystal structure). It is an example of wave-particle duality
Term
 Electron flow
Definition
 The movement of electrons (usually around a circuit) from - to +.
Term
Definition
 A form of electromagnetic wave with a wavelength between (10^-1) and (10^4)m.
Term
 Potential difference
Definition
 The elctrical energy transferred per unit charge when electrical energy is converted into some other form of energy.
Term
 Potential divider
Definition
 A type of circuit containing two components designed to divide up the P.D in proportion to the resistances of the components.
Term
 Plane polarised wave
Definition
 A transverse wave oscillating in one plane only.
Term
 Polarisation
Definition
 The process of turning an unpolarised wave into a plane polarised wave.
Term
 Photoelectric effect
Definition
 The emission of electrons from the surface of a material when electronmagnetic radiation is incident on the surface
Term
 Photon
Definition
 A quantum of light, often described as a particle of light.
Term
 Plancks constant
Definition
 Constant used in physics. h=6.63x10^-34 Js
Term
 Ultraviolet
Definition
 A form of electromagnetic wave with wavelengths of (10^-9) to (3.7x10^-7)
Term
 Volt
Definition
 Unit of P.D 1V = 1JC^-1
Term
 Watt
Definition
 Unit of Power 1W = 1Js^-1
Term
 Voltmeter
Definition
 A device used to measure the P.D across a component. It is connected in parallel.
Term
 Line spectrum
Definition
 A spectrum produced by a material that contains only certian frequencies due to electron transistions between energy levels.
Term
 Malus' law
Definition
 A physical law describing the change in intensity of a transverse wave passing through a polaroid analyser.
Term
 Microwaves
Definition
 A form of electromagnetic wave with wavelengths between (10^-4) and (10^-1)m.
Term
 Reflection
Definition
 When waves rebound from a barrier, changing direction but remaining in the same medium.
Term
 Refraction
Definition
 When waves change direction when they travel from one medium to another due to a difference in the wave speed of each medium.
Term
 Transverse waves
Definition
 A wave in which the oscillations are at a right angle to the direction of travel.
Term
 Conservation of energy
Definition
 Physical law stating that energy cannot be created or destroyed, but can be transformed from one form to another.
Term
 Kirchhoff's 1st law
Definition
 The sum of the currents entering any junction is also equal to the sum of the currents leaving the junction.
Term
 Kirchhoff's 2nd law
Definition
 The sum of the E.M.Fs is equal to the sum of the P.Ds in a closed loop.
Term
 Longitudinal waves
Definition
 A wave where the oscillations are parallel to the direction of the wave.
Term
 Superposition
Definition
 The principle that states that when two or more waves of the same type exist at the same place the resultant wave will be found by adding the displacements of each individual wave.
Term
 Amplitude
Definition
 The maximum displacement of a wave from its mean position, measured in metres.
Term
 Frequency
Definition
 The number of oscillations per unit time, measure in Hertz.
Term
 Period
Definition
 The time taken for one complete pattern of oscillation, measured in seconds.
Term
 Displacement (waves)
Definition
 The distance any part of the wave has moved from its mean, measure in metres.
Term
 Phase difference
Definition
 The difference by which one wave leads or lags behinds another, measured in radians.
Term
 Resistance
Definition
 V=IR. A property of a component that regulates the electric current through it. Measured in ohms.
Term
 Electric charge
Definition
 Q=IT. Measured in Coloumbs
Term
 Electric current
Definition
 A flow of charge. Measure in amperes and is a vector quantity.
Term
 Visible light
Definition
 A form of electromagnetic wave with wavelengths of (3.7x10^-7) to (7.4x10^-7)m
Term
 X rays
Definition
 A form of electromagnetic wave with wavelength of (10^-12) to (10^-7)m.
Term
 Threshold frequency
Definition
 The minimum frequency needed to free an electron from the surface.
Term
 Coherent sources
Definition
 Wave sources that have a constant phase difference.
Term
 Principle of superposition of waves
Definition
 Constructive interference/waves in phase. Maxima produced when path difference is 0 or nλ. Minima produced when path difference is (n+1/2)λ.
Term
 How is a standing wave formed?
Definition
 Waves travel out fropm the centre and are reflected then interference /superpositioning occurs.
Term
 Explain the changes in an ammeter and a voltmeter when the temperature of a NTC thermistor is increased.
Definition
 The resistance of the thermistor decreases as the temperature increases.The total resistance of the circuit decreases.The voltmeter reading decreases.The current increases.
Term
 Does intensity change the energy of a photon?
Definition
 NO.
Term
 In waves, what is the relationship between intensity and amplitude?
Definition
 Intensity ∝ Amplitude^2.
Term
 What are the charge carriers in metal?
Definition
 Electrons.
Term
 What is the equation for drift velocity?
Definition
 I = nAvq
Term
 Are ionic crystals insulators?
Definition
 Yes and no. When molten it is a conductor as the free ions are the charge carriers. It is an insulator under its normal physical state as there is very little charge carriers.
Term
 In what situations do gases conduct electricity?
Definition
 Under a very high voltage.
Term
 Wht is the charge of an electron?
Definition
 1.6x10^-19 J.
Term
 What does a curve on a I/V characteristic graph mean?
Definition
 A changing resistance.
Term
 How does temperature affect the resistance of a metal wire? why does it affect it?
Definition
 It increases the resistance as the ions vibrate more due to the extra kinetic energy, the electrons then collide with them more often, losing energy.
Term
 What does LDR stand for?
Definition
 Light dependant diode.
Term
 What is a forward bias?
Definition
 It is the direction the current is allowed to flow in a diode.
Term
 What is the equation for power?
Definition
 P = IV, P = V^2/R, P = I^2R
Term
 What is the equation for total energy transferred?
Definition
 E = VIt , E = I^2Rt, E = V^2/Rt, P = Et
Term
 What values of fuses do you get?
Definition
 3A and 13A (sometimes 5A).
Term
 Why does a battery have resistance?
Definition
 As the electrons move in the battery, they collide with the atoms in the battery - causing an internal resistance.
Term
 What is a "lost volt"?
Definition
 It is the energy wasted per coulomb overcoming the internal resistance.
Term
 What are the equations to do with E.M.F?
Definition
 e = V + v, e = I(R+r), e = V + Ir.
Term
 In what type of circuit is the P.D the same across all components?
Definition
 Parallel.
Term
 In what type of circuit is the current the same across all points of the circuit?
Definition
 Series.
Term
 What is the equation for the speed of a wave?
Definition
 v = λf
Term
 When unpolarised light reflects, does it become partially polarised?
Definition
 Yes.
Term
 What do all EM waves have in common?
Definition
 They all travel at the same speed in a vacuum.They obey v = λf.They are all transverse waves.
Term
 Which EM wave has the most energy?
Definition
 Gamma rays.
Term
 Which EM wave has the least amount of energy?
Definition
Term
 Principle of superposition
Definition
 When two or more waves cross, the resultant displacement equals the vector sum of the individual displacements.
Term
 In phase
Definition
 The two points are at the same point in the wave cycle.
Term
 What conditions are required to get an interference pattern?
Definition
 The two sources must be coherent.
Term
 Standing wave
Definition
 The superposition of two progressive waves with the same wavelength, moving in oppersite directions.
Term
 In what conditions do you get the most diffraction from a gap?
Definition
 When the gap is the same size as the wavelength.
Term
 If the gap in diffraction is smaller than the wavelength, what happens to the waves?
Definition
 They are mostly reflected back.
Term
 Why do you use lasers in young's double slit experiment?
Definition
 Because it is coherent and monochromatic.
Term
 What is the equation for the fringe spacing in young's double-slit experiment?
Definition
 x = (Dλ)/dx - fringe spacingλ - wavelengthD - distance from slits to screend - spacing between slits
Term
 How do you make interference patterns sharper?
Definition
 By diffracting the light through more slits.
Term
 What is the equation used for diffraction grating?
Definition
 dsinθ = nλ
Term
 When you diffract white light through a diffraction grating and produce a spectra, where you find the red and violet wavelengths?
Definition
 Red - OutsideViolet - Inside
Term
 What are the equations expressing the energy carried by a photon?
Definition
 E = hf = (hc)/λ
Term
 Why isnt photons measured in joules?
Definition
 Because it has such a tiny energy that is makes sense to have a smaller unit.
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