Physics Definitions Unit 2

Units 1, 2, 3, 4, 6

Define ‘electric current’ (conduction of electricity)

Flow of electrons around a circuit

Which way do electrons flow? (conduction of electricity)

from negative to positive

Which was does CONVENTIONAL CURRENT flow? (conduction of electricity)

from positive to negative

Define ‘current’ (conduction of electricity)

rate of flow of charge (I=Q/T)

Define ‘electron drift velocity’ (conduction of electricity)

small net velocity causing electrons to move in one direction.

What is the ‘Thermal motion’ in electrons? (conduction of electricity)

The normal, random and very fast movement of electrons

What is the ‘E-field motion’ in electrons? (conduction of electricity)

The motion of electrons due to the influence of an electric field, resulting in a directed flow of charge from negative to positive

What is the drift velocity made up of? (2 components) (conduction of electricity)

Thermal Motion and E-Field Motion

Define ‘potential difference’ (conduction of electricity)

The energy transferred per unit charge by charges in moving between two points in the circuit

Define ‘Electro-motive force’ of a cell (conduction of electricity)

The energy transferred by the cell to unit charge in passing through the cell

Define ‘resistance’ (resistance)

opposition of the circuit or potential difference across a wire per unit charge

What are the factors that effect the resistance of a wire? (4)(resistance)

Length, CSA, Temperature, Material

Define ‘ohm’ (resistance)

Resistance of a conductor when a a pd of 1 volt across it produces 1 amp through it

Name 3 types of semiconductors (resistance)

diode, LDR, thermistor

Define ‘superconductor’ (resistance)

A material that suddenly loses ALL electrical resistance at low temperatures

What is the temperature at which superconductors resistance is 0? (resistance)

the superconducting transition temperature

Name 3 types uses for superconductors (resistance)

Particle accelerators, Tokamaks, MRIs

Define ‘photoelectric effect’ (photons)

The emission of electrons from a metallic surface when electromagnetic radiation of a high enough frequency is incident on it

Define ‘photon’ (photons)

packet of e/m radiation

Define ‘work function’ (photons)

Minimum amount of energy required to remove an electron from a material's surface.

Define ‘energy level’ (photons)

particular energy value of an electron

What are the 2 types of circuits? (DC Circuits)

Series and Parallel

Define ‘Kirchoff’s first law’ (DC Circuits)

At any junction in a circuit, the sum of the currents arriving at the junction is equal to the sum of the currents leaving the junction

Define ‘Kirchoff’s second law’ (DC circuits)

In any loop (path) around a circuit, the sum of the emfs is equal to the sum of the pds

Define ‘terminal pd’ (DC Circuits)

total energy output of the cell (including internal resistance)

Define ‘Ohms Law’ (resistance)

The pd across a wire is proportional to the current, provided the temperature and dimensions of the wire remain constant

Define ‘transverse wave’ (waves)

oscillations are perpendicular to the direction of energy transfer

Define ‘Longitudinal Wave’ (waves)

oscillations are parallel to the direction of energy transfer

Define ‘progressive wave’ (waves)

transfers energy without transferring matter

Define ‘displacement’ (waves)

The distance moved by a particle from its equilibrium position

Define ‘Wavelength’ (waves)

The distance between consecutive repeating parts of a wave

Define ‘frequency’ (waves)

The number of waves passing a fixed point per second

Define ‘velocity’ (waves)

The distance travelled per unit time by a wave

Define ‘Amplitude’ (waves)

The maximum displacement of a particle in a wave

Define ‘Period’ (waves)

The time taken for one wave to pass a fixed point

Define ‘antiphase’ (waves)

When a wave is 180° out of phase

(or one wave is leading another by 90°

Define ‘the principle of superposition’ (waves)

The resultant displacement at a point is the vector sum of the individual wave displacements (the waves then pass through each other as if nothing happened’

Define ‘constructive interferance’ (waves)

When two waves meet and their energies add together temporarily

Define ‘Deconstructive interference’ (waves)

When two waves meet and cancel each other out temporarily

Define ‘coherant waves’ (waves)

waves that have a constant phase difference

• they are normally produced from the same source

Define ‘path difference’ (waves)

the difference in distance travelled by two waves in order to arrive at a single point

How many wavelengths is this stationary wave on a string? (waves)

½

How many wavelengths is this stationary wave in a tube? (waves)

¼

Define ‘node’ (waves)

points on two stationary waves in antipahse, so that destructive interference occurs

Define ‘anti-node’ (waves)

points on two stationary waves in phase , so that constructive interference occurs

When are stationary waves formed? (waves)

when identical waves from opposite directions superimpose

Difference between progressive and stationary waves (amplitude)

Progressive

• constant amplitude (or amplitude decreases with distance)

Stationary

• max amplitude at anitnode, gradually decreasing to zero at node

Difference between progressive and stationary waves (Energy)

Progressive

• transfers energy without transferring matter

Stationary

• energy usually fixed between 2 points

Difference between progressive and stationary waves (Phase)

Progressive

• Phase lag increases with distance from source

Stationary

• in a loop, everything in phase. Next loop is in antiphase

Define ‘absorption’ (lasers)

electron absorbs a photon and jumps to a higher energy level

Define ‘spontaneous emmission’ (lasers)

Electron randomly drops to ground state and releases a photon of the same energy (random direction and phase)

Define ‘Stimulated emission’ (lasers)

Electron is stimulated to drop from an excited state by an incoming photon and will lead to LIGHT AMPLIFICATION

Define ‘light amplification’ (lasers)

When one incoming photon results in 2 photons being emitted (same energy, frequency, direction and phase)

Define ‘population inversion’ (lasers)

more electrons in higher levels than lower ones

Define ‘pumping of electrons’ (lasers)

supplying electrons with energy to jump to higher energy levels