definitions and explanations for ocr physics g482
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Definitions and Explanations for OCR Physics G482TRANSCRIPT
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