Definitions for Physics G482

The Net flow of charged particles Vector Quantity () 1 A = 1 C/s Caused by electrons in a metal Caused by ions in an electrolyte Caused by protons/anti-protons in a PartAccel Caused by conduction electrons and holes in a

semiconductor

Electric Current

Model used to describe the movement of

charge in a circuit. Conventional travels from + to -

Conventional current

The movement of electrons (normally round a

circuit) Electrons flow from – to +

Electron Flow

The standard unit for charge equal to the quantity of electricity conveyed in

one second by a current of one ampere

1 C = 1 As

Coulomb

A device used to measure the current in a

circuit connected in series with the components

Ammeter

The sum of the current entering a junction is

equal to the sum of the current leaving a junction

This is a consequence of the conservation of charge

Kirchoff’s First Law

The average displacement travelled of the electrons along the wire per

second

Number density refers to the available electrons for conduction. Conductors have huge numbers of free electrons.

Insulators have none or extremely few because they have full electron shells.

Semiconductors are "doped" to create hole/electron pairs in a so called p-n junction region that allows conduction to be turned on and off by the strength and direction of the electric field in the p-n junction. The number density in semiconductors is thus much less than in conductors and is artificially created by doping. Without doping, semiconductors have a number density between conductors and insulators.

Doping enforces specific impurities which allow conduction

Mean Drift Velocity

Positive negative junction Formed between the boundary of a

semiconductor with + and – parts.

P-N Junction

Positive Negative

Junction

The electrical energy transferred per unit

charge when electrical energy is converted into some

other form of energy

Potential Difference

The electrical energy transferred per unit

charge when some other form of energy is converted

into electrical energy

All sources of emf have internal resistance

Electromotive Force

Unit of potential difference and e.m.f.

Energy = Volt Charge 1 V = 1 J/C

Volt

A device used to measure the p.d. across a

component

It is connected in parallel across a component

Voltmeter

Resistance A property of a component that regulates the electric current

through it. Measured in Ω (Ohms)

Resistance of a metal increases with temp as the atoms of the metal attain more kinetic energy caused by vibrations. The electrons therefore have to travel through more turbulent atoms, meaning more resistance

Thermistors with an NTC have a decrease in resistance with an increase in temperature

Ω (Ohm) Unit of resistance 1 Ω = 1 V/A

Ohm’s Law The electric current through a conductor is proportional to the

p.d. across it Provided physical conditions, such as temperature, remain

constant

Resistivity is a measure of how strongly a material opposes the flow of

electric current The ratio of the product of resistance and cross-sectional

Area of a component and its length electrical resistivity of metals increases with temperature the resistivity of intrinsic semiconductors decreases with

increasing temperature

Power The rate of doing work The rate of energy transfer Measured in W (Watts) 1 W = 1 J/s

Fuse An electrical component used to heat up, melt and break the

circuit (hence stop the current) when a specified amount of electric current passes through it. Used as a safety device

The fuse used should always be a bit higher than the Current specified by the power rating and voltage rating

Slow Blow fuse A double helix fuse capable of withstanding short surges of

current through it

Energy transferred = P.d. x Current x Time

Measured in Joules

W = VIt

A Unit of Energy The energy transferred when 1000W is

used for 3600s, equal to 3.6 MJ

Kilowatt-hour (kWh)

Cost of using an appliance = cost per one kWh number of kWh’s used

kWh-cost ratio

The sum of the e.m.f.s is equal to the sum of the p.d.s in a closed loop

This is a consequence of a conservation of energy

+

Kirchoff’s Second Law

Potential difference (pd) or voltage across the terminals of a power supply, such as a battery of cells. When the supply is not connected in circuit its terminal voltage is the same as its electromotive force (emf)

however, as soon as it begins to supply current to a circuit its terminal voltage falls because some electric potential energy is lost in driving current against the supply's own internal resistance. As the current flowing in the circuit is increased the terminal voltage of the supply falls.

Terminal p.d.

E is Emf V is voltage of components I is the current r is the internal resistance

Equation for emf

The potential of the voltage source is dividied into the ratio of the resistances (ie R1 will have a pd of across it)

This means you can choose the resistances to get the voltage you want across one of themPotential Divider

Intensity of light increases, resistance decreases

LDR

LDRs and thermistors are highly useful in these circuits as the voltage can be change continuously

This is useful in appliances such as a stereo to continuously adjust the volume

NTC Resistors in Potential Dividers

an additional advantage of using a thermistor in a potential divider is that it produces an electrical output V0, which may be used as an input to a datalogger, if a continuous record of a temperature is required

The advantage is that you can use a datalogger to record a significant change in resistance for a very small (and otherwise difficult to record) change in temperature.

Data Logging with Potential dividers and thermistors

Transv

ers

e W

ave A wave where the

oscillations are perpendicular to the

direction of wave propagation

Longit

udin

al

Wave A wave where the

oscillations are parallel

to the direction of wave propagation

Dis

pla

cem

ent

The distance any part

of a wave has moved

from its rest position

Am

plit

ude The maximum

displacement ie the distance from peak to

restAlways positive as it

only concerns magnitude

Wave

length

The smallest distance

between two points that have the same pattern of oscillation.

The distance the wave

travels before it repeats itself

Peri

od

The time for one complete pattern of oscillation to take place at any point

Phase

Diff

ere

nce

The difference by which one wave leads

or lags behind another

Frequency

The number of oscillations per unit time at any point

Speed o

f a w

ave The distance travelled

by the wave per unit

time

Reflect

ion When waves rebound

from a barrier, changing direction but

remaining in the same

medium

Refr

act

ion When waves change

direction when they travel from one medium to another due to a difference in

the wave speed in each medium

Diff

ract

ion

Whena wave spreads

out after passing through an obstacle or

gap

Plane polarised wave

A transverse wave oscillating in only one plane

Light is partially polarised on reflection

Malus’ Law

A physical law describing a change in intensity of a transverse wave passing through a Polaroid analyser

Superposition

The principle that states When two or more waves exist at the

same place The resultant wave can be found by

adding the displacements of each individual wave

Interference

The addition of two or more waves (superposition)

That results in a new wave pattern

Coherence

Two or more waves with a constant phase relationship

Path Difference

the difference in distance travelled by the two waves from their respective sources to a given point on the pattern

Constructive Interference

Occurs when the path difference = nλ

When a crest meets a crest between two waves

Destructive Interference

Occurs when the path difference = λ

When a crest meets a trough between two waves (ie antiphase)

Sound Interference experiment

O Sig GenO Two speakersO Places of intensity (antinodes – con.

Interference)O Places of quietness (nodes – dest.

Interference)

Light Interference Experiment

O Feynman’s Two Slit experimentO The light waves enter the slits, and

start spreading coherently towards a wall

O The waves superimpose, forming an interference pattern

Microwave Interference Experiment

O A Waveguide can be used to split microwaves into two different paths before re-joining

Path A

Path B

Intensity Relationships

Young double-slit experiment

O An experiment to demonstrate the wave nature of light via superposition and interference

O a is the slit spacingO x is the fringe widthO D is the distance to the wall

Diffraction GratingO Advantage is that from each grating,

each ray will travel exactly one wavelength further than the ray directly above it

O Therefore, all rays will be in phase with one another – they will reinforce to give a maximum intensity

Diff. Grating Equation

O d is the spacing between slits

NodeO A point along a stationary wave

where there is 0 amplitude due to destructive interference

AntinodeO A point along a stationary wave

where there is max amplitude due to constructive interference

Fundamental mode of vibration

O The lowest frequency in a harmonic series where a stationary wave forms

HarmonicsO Whole number multipliers of the

fundamental mode of vibration

EMR was described as Planck to be a stream of particles called photons

PARTICULATE NATURE OF EMR

A Quantum of light, often described to be a particle of light

PHOTON

1 eV is the energy change of an electron when it moves through a p.d. of 1 V

1 eV = 1.6×10 -19 J

ELECTRONVOLT

Used for electrons and other charged particles

TRANSFER EQUATION

electrons are emitted from a material surface as a consequence of their absorption of energy from

electromagnetic radiation of very short wavelength such as visible or ultraviolet light. Electrons emitted in this manner may be referred to

as "photoelectrons"

PHOTOELECTRIC EFFECT

the minimum energy (usually measured in electron volts) needed to remove an electron from a solid to a point immediately outside the solid surface

(or energy needed to move an electron from the Fermi level into vacuum)

WORK FUNCTION

The lowest frequency of EMR that will result in the emission of photoelectrons from a specified metal surface

THRESHOLD FREQUENCY

The energy is conserved when a photon interacts with an electron

C OF E BETWEEN PHOTONS AND ELECTRONS

Max KE of electrons is independent of intensity because electrons can only absorb one photon at a time

The KE does depend on the frequency of light however…

MAX KE OF ELECTRONS IS INDEPENDENT OF INTENSITY

an increase in intensity (more photons) will produce an increase in photoelectric emission

PHOTOELECTRIC CURRENT IS PROPORTIONAL TO THE INTENSITY OF INCIDENT LIGHT…

The rate at which the electrons are emitted from a photo cathode is independent of its temperature.

PHOTOCATHODES AND TEMP RELATIONSHIP

Voltage required to stop the outward movement of electrons emitted by photoelectric or thermionic action.

For a given metal surface, stopping potential (Vo) is directly proportional to frequency but independent of intensity.

STOPPING POTENTIAL

λ=h

𝑚𝑒𝑣

DE BROGLIE’S EQUATION

Used to determine the atomic spacing and arrangement of atoms

The size of nuclei

Diameter of a nucleus

ELECTRON DIFFRACTION USES

ENERGY LEVEL

One of the specific energies an electron can have within an atom

EMISSION LINE SPECTRA

Hot Gases emit light – Emission Spectra Cool Gases absorb white light – Absorption Spectra