Physics_Module_1_revision_notes

8/7/2019 Physics_Module_1_revision_notes

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Prefixes to know:

nano micro milli kilo mega gigan m k M G

10-9 10-6 10-3 103 106 109

~*~*~*~*~ELECTRICITY~*~*~*~*~

Equations:

Q = It

V =QW

E = IVt

V = IR

P = IV

P = I2R and P =R

V2

l

RA=

Definitions based on these equations:

Q = charge measured in C

I = current measured in At = time measured in s

V = p.d. measured in V

W = work done measured in J

E = energy (work done) measured in J

R = resistance measured in

P = power measured in W

= resistivity measured in m

A = X-sectional area measured in m2

l= length measured in m

Current is the rate of flow of charge Potential difference is the work done

per unit charge

Emf is the electrical energy produced

per unit charge passing through the

source

Resistance is a measure of the

difficulty of making current pass

through a componentPower is defined as the rate at which

electrical energyis transferred by an

electric circuit

Resistivity is a measure of how

strongly a material opposes the flow

of electric current
http://en.wikipedia.org/wiki/Electrical_energyhttp://en.wikipedia.org/wiki/Electric_circuithttp://en.wikipedia.org/wiki/Electrical_energyhttp://en.wikipedia.org/wiki/Electric_circuit


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Ohms Law: states that the pd across a metallic conductor is proportional to

the current through it, provided the physical conditions do not

change.

The graphs below show the current against pd for different components:

Superconductors: A superconductor is a wire or device made frommaterial that has zero resistivity at and below a critical

temperature (specific to the material). The wire

therefore has zero resistance below this temperature

and when current passes through it, there is no pd across

wasted.

Circuits

Symbols you must learn!+ -

A

V

Thermistor

V

I Diode

V

IWire

V

I Lamp

V

I

0.6

SwitchLamp

Lamp

Lamp

Variable resistor

Cell

Resistor

Ammeter

Diode

Voltmeter

Variable resistor /

Potential divider

I

+ -

R

I electrons

+ -

R

electrons

Electron

flow:


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Conventional

current

flow:

Rules for current and potential difference:In series In parallel

Current The current across components

in series is the same

The sum of the currents in a

parallel circuit add to the

current through the cell or

battery

Potential difference The sum of the pds across all

the components is equal to the

supply pd

The pd across components in

parallel is the same

*Current splits at a junction and will split in the opposite ratio to the

resistance in each branch*

Resistors in series: RT= R1 + R2 + R3 etc

Resistors in parallel:321

1111

RRRRT++= etc

Internal resistance, r, is due to the opposition to the flow of charge

through the source.

When plotting a graph of V against I, should get:

Y-axis intercept is Gradient is r

The Potential Divider

Theory: A potential divider circuit consists of 2 or more resistors in series,and a source of fixed pd. The pd of the source is divided between the

resistors (and any other component in series). Uses are:

To supply a pd which is fixed at any value between 0 and source pd

To supply a variable pd

To supply a pd that varies with a physical condition, eg temperature

In the circuit shown:

Q

E= IrIR+=

p.d./V

I/A

I

12V

(V0)

V1

V2

R1

R2

pd across R1 =21

1

RR

R

+x V0

pd across R2 = 21

2

RR

R

+ x V0


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Some possible circuits using a potential divider:

AC Current

Oscilloscopes

You need to be able to read the scale on the x-axis (time base)

and the y-axis (voltage). Then work out the frequency from the

time base using:

The oscilloscope may be used as a voltmeter:

Screen

Zero

Line

A.C. trace

Peak

VoltagePeak-Peak

Voltage

Brightness control using a

variable potential divider A temperature sensor A light sensor

2

0V

Vrms = 2

0I

Irms =

Tf

1=

Applied pd = 0V

Applied pd = +4V


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~*~*~*~*~PARTICLES~*~*~*~*~

The atom consists of a positively charged nucleus, composed of protons and

neutrons.

Electrons orbit the nucleus in outer shells

Isotopes are atoms of the same element with the same number of protons

but different numbers of neutrons.

Isotopes are labelled as:

Specific charge of a charged particle =mass

ech arg

The four fundamental forces:

Force Exchange particle Acts on Range

Gravity Graviton All particles Infinite

Electromagnetic Photon Charged particles Infinite

Strong interaction Gluon Hadrons ~10-15m

Weak interaction W+, W-, Z0 All particles ~10-18m

Applied pd = -3V

Mass or nucleon

number. It is the

number of

protons and

neutrons

U238

92

Atomic number.

It is the number

of protons only.


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Classification ofparticles:

Some facts!

Hadrons:interact through thestrong interaction and decay through the

weak interaction

Leptons: only interact through the weak interaction and the electromagnetic

interaction if they are charged

Baryons are protons and all other hadrons that decay into protons, either

directly or indirectly.

Mesons are hadrons that do not include protons in their decay products.

Alpha particle emission: An unstable nucleus may emit an alpha particle (2

protons and 2 neutrons.

Showing reactions using Feynman Diagrams:

leptons

baryons

qqq / qqq

Mesons

q q

hadrons

All particles(matter and

antimatter).

0: uu+: du-: ud

Baryons:

Proton: uudAntiproton: duuNeutron: udd

Antineutron: ddu

Mesons:

K0: sd

K+: suK-: us

Leptons:

particle antiparticle

electron, e- positron e+

muon, - antimuon, +

electron neutrino, e electron antineutrino, muon neutrino, muon antineutrino,

4

2

4

2 +

YX

A

Z

A

Z


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Conservation lawsCharge, Baryon number, Lepton number and sometimes strangeness must be

conserved. The tables below are to be used. Remember for quarks, they are

1/3 of a baryon, so take 1/3 of the charge and baryon number.

Annihilation and Pair ProductionAnnihilation is the conversion of the mass of a particle and its

antiparticle to energy in the form of a pair of photons of EM radiation.

When an electron and a positron (or a proton and an antiproton, etc.) collide

they may annihilate each other. Both the electron and the positron cease to

exist and two g ray photons are created. It is impossible for there to be

just one photon for this would not allow both energy and momentum to be

conserved.

neutron-neutrino

collision

e

enp +++

eepn ++

Electron capture

ray

E = 511 keV

e

nep ++

electron

ray

++ epne

positron

+ decay

E = mc2

Where E is energy, m is

mass and c = 3 x 108ms-1

+

++ enpe

- decay proton-antineutrinocollision


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Pair production is the process in which a photon of EM radiation ceases

to exist, creating a particle and its antiparticle pair in its place.

~*~*~*~*~THE PHOTOELECTRIC EFFECT~*~*~*~*~

Equations:E = hf

hf = EK +

hf

=min

hf = E1 E2

mv

h=

E = energy measured in J

h = Plancks constant: 6.63 x 10-34

f = frequency measured in Hz

EK = max kinetic energy measured in J

= work function measured in J

fmin = threshold frequency measured in J

= wavelength measured in m

m = mass measured in kg v = velocity measured in ms -1

Thework functionof a metal is the

minimum energy needed by an

electron to escape from the metal

Thethreshold frequencyis the

minimum frequency of light needed to

remove an electron from the surface

of a metal.

Excitationof an electron (or atom)

can occur by either collision with an

electron or absorption of a photon.

Both result in the electron being

raised to a higher energy orbit.

Fluorescenceoccurs when a gas (eg

mercury) in a tube at low pressure has

an electric current passing through it.

Electrons collide with orbitingelectrons from the mercury atoms

and excite. When they de-excite they

emit photons of UV light which are

absorbed by the coating in the tube.

These atoms therefore excite, and

they then de-excite to the ground

state indirectly, emitting photons of

smaller wavelength which are in the

visible spectrum of light.

Ionisationof an atom is when thenumber of electrons in an atom is not

equal to the number of protons. The

atom has either gained or lost

electrons.

The electronvolt (eV):1 eV = 1.6 x 1O-19 J

Wave Particle Duality means that

electrons display both particleproperties and wave properties,

though not simultaneously.

Example of particle behaviour:

deflection due to an electric field.

Example of wave behaviour: electron

diffraction tube.

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