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OCR Physics A - G482
Definitions required for the Electrons, Waves & Photons paper
48
Physics
11th Grade
10/05/2012

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Term
Electric current
Definition
Net movement of charge
Term
Coulomb
Definition
1 C is the charge transferred in 1 second by a current of 1 amp
Term
Potential difference (p.d.)
Definition
The electrical energy transferred per unit charge when electrical energy is converted into another form of energy
Term
Electromotive force (e.m.f.)
Definition
The energy transferred per unit charge when another type of energy is converted into electrical energy
Term
Volt
Definition
1 V is 1 joule per coulomb
Term
Resistance
Definition
Resistance is potential difference per unit current
Term
Ohm
Definition
1 ohm is the resistance when 1 volt of potential difference produces 1 ampere of current
Term
Resistivity
Definition
resistivity = (resistance * cross-sectional area)/length
Term
Kilowatt-hour
Definition
1 kWh is the energy transferred by a 1 kW device in a time of 1 hour
Term
Terminal p.d.
Definition
The potential difference across the total external resistance connected to an e.m.f. source
Term
Progressive wave
Definition
A wave that carries energy from one place to another
Term
Transverse wave
Definition
A wave in which the oscillation is perpendicular to the direction of travel of the wave
Term
Longitudinal wave
Definition
A wave in which particles oscillate parallel to the direction of travel of the wave
Term
Node
Definition
A point on a stationary wave where the amplitude is zero
Term
Anti-node
Definition
A point on a stationary wave where the amplitude is a maximum
Term
Principle of Superposition
Definition
When two or more waves of the same type are in the same place at the same time, the resultant displacement is the sum of the displacements of the individual waves
Term
Amplitude
Definition
The maximum displacement of any point on a wave from its equilibrium position; it is always positive
Term
Wavelength
Definition
The smallest distance from a point on a wave and a similar point on the next wave
Term
Period of a wave
Definition
The time taken for one complete oscillation of a point on a wave
Term
Frequency
Definition
The number of oscillations per unit time of any point
Term
Electron-volt
Definition
1 eV is the energy change of an electron when it moves through a potential difference of one volt
Term
Work function
Definition
The minimum energy required to release an electron from the surface of a metal
Term
Threshold frequency
Definition
The minimum frequency of electromagnetic radiation required to release an electron from the surface of a metal
Term
Mean drift velocity
Definition
The average velocity of a charge carrier as it travels through a medium due to a potential difference.
Term
Ohm's Law
Definition
The current through a conductor is proportional to the potential difference across it at a constant temperature
Term
Displacement
Definition
The distance any part of the wave has moved from its mean position; it can be positive or negative.
Term
Phase difference
Definition
Angular difference by which one wave or particle leads or lags behind another
Term
Speed of a wave
Definition
The distance moved by the wave per unit time
Term
Coherent
Definition
Waves with a constant phase difference (same frequency)
Term
Fundamental mode of vibration
Definition
The lowest frequency stationary wave for a particular system
Term
Harmonics
Definition
Stationary waves for a particular system with higher frequencies than the fundamental
Term
Conventional current
Definition
Direction is from positive to negative
Term
Kirchoff's 1st Law
Definition
The sum of current entering any point in a circuit is equal to the sum of the currents leaving that same point
Term
Kirchoff's 2nd Law
Definition
The sum of e.m.f.s round a loop in a circuit is equal to the sum of p.d.s in that same loop
Term
Power
Definition
The rate of energy transfer
Term
Reflection
Definition
The bouncing back of a wave from a surface
Term
Refraction
Definition
The change in direction of a wave as it crosses an interface between two materials where its speed changes
Term
Diffraction
Definition
The spreading of a wave when it passes through a gap or past the edge of an object
Term
Typical wavelength of radio waves
Definition
10^1 m
Term
Typical wavelength of microwaves
Definition
10^-2 m
Term
Typical wavelength of infra-red radiation
Definition
10^-5 m
Term
Typical wavelength of visible light
Definition
4x10^-7 to 7x10^-7 m
Term
Typical wavelength of ultra-violet radiation
Definition
10^-8 m
Term
Typical wavelength of X-rays
Definition
10^-11 m
Term
Typical wavelength of gamma radiation
Definition
10^-11 m
Term
Plane polarised wave
Definition
A transverse wave that oscillates in only one plane
Term
Constructive interference
Definition
When two or more waves meet in phase; the amplitudes add
Term
Destructive interference
Definition
when two or more waves meet in anti-phase; the amplitudes subtract
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