Transcript Module 1 in 10 minutes

Particles, Quantum Phenomena
and Electricity
4 Fundamental Forces




Gravity
Electromagnetic
Weak nuclear
Strong nuclear




gravitons
photons
W bosons (and Z boson)
Pi mesons (pions)
Any particle with mass
Any charged particle
All leptons, baryons and mesons
Hadrons
Alpha Particle Scattering
• Nucleus is tiny
• Nucleus is massive
• Nucleus is very dense
• Atom is mostly free
space
Quantum Phenomena
Annihilation
- The conversion of mass to energy
- 2 gamma ray photons released
Quantum Phenomena
Pair Production
- The conversion of energy to mass
- A gamma ray photon of sufficient energy
may decay into an electron and a positron
Particle Families
Leptons – Fundamental particles
Leptons = Lepton No. of +1
Anti-leptons = Lepton No. of -1
Not a Lepton = Lepton No. of 0
Particle Families
Hadrons – Composed of quarks
Baryons = Baryon No. of +1
Anti-baryon = Baryon No. of -1
Not a Baryon = Baryon No. of 0 (Including mesons)
Particle Families
Some
particles:
Feynmann Diagrams
EM Interaction
Feynmann Diagrams
Weak Interaction (Beta minus)
Feynmann Diagrams
Weak Interaction (Beta plus)
Feynmann Diagrams
Weak Interaction (Electron capture)
Feynmann Diagrams
Weak Interaction (Electron-proton collision)
β- (neutron) Decay
A
Z
X
Y   
A
Z 1
0
1
0
0 e
The quark structure of the neutron is udd
In β- decay a down quark changes to an up quark.
uud = +2/3 +2/3 -1/3 = 1
The neutron (Q = 0) has changed into a proton (Q = 1).
neutron (udd) → proton (uud)
β+ (proton) Decay
A
Z
X Y    
A
Z 1
0
1
0
0 e
In β+ decay an up quark in a proton changes to a
down quark.
This only happens in proton-rich nuclei.
proton (uud) → neutron (udd)
Particle Interactions
The 4 quantities (Q, B, S and L) have to
be the same after a reaction as they
were before it occurred.
Important:
Strangeness is only conserved in
the strong and electromagnetic
interactions.
19
1eV  1.6x10
J
The electronvolt is an amount of energy
equal to the above value.
It is arrived at by applying the equation
E= QV to an electron accelerated by a p.d.
of 1Volt.
Photoelectric Effect
hf = φ + Ek (SI Units)
Energy Levels and electron
excitation
E = hf
Fluorescent Tube
Wave-particle Duality
The Photoelectric Effect suggests the
particle nature of light.
Electron diffraction suggests the wave
nature of particles.
deBroglie
Wavelength,
h
h
λ  or λ 
p
mv
Q  It
E  QV
W
P
t
E  ItV
R
V  IR
l
A
P  IV
Series circuits:


Current same at all points
– it is a continuous flow.
Voltage shared between
components.
24
Parallel Circuits


Voltage same across
branches as that of power
source.
Current splits between
branches (splits and rejoins
at junctions).
25
Cells in Series and Parallel
Using Ammeters



Ammeters measure the current flowing
through themselves.
Ammeters are placed in series.
The ideal ammeter ought to have zero
resistance.
Using Voltmeters



Voltmeters measure the voltage
between two places.
This is also called potential difference.
(The difference in the “push” between
two places)
Voltmeters are placed in parallel.
I-V Characteristics
Thermistors – Resistance decreases as temperature increases
LDR – Resistance decreases as light intensity increases
Resistors in Series
Easy!
R  R1  R2  R3
Resistors in Parallel
1
RParallel
1
1
1



R1 R2 R3
Resistor Combinations
1
1
1
1
2




RParallel 20 20 30 15
1
1
1
R

20




30
15
Total
RParallel  20
 7.5Ω
20 30
2
RTotal  7.5  20  30  57.5Ω
Potential Dividers
V=
R
R Total
×VTotal
What is the p.d. across each of the two resistors?
12V across each as they are equal resistance
Potential Dividers
V=
R
R Total
×VTotal
What is the p.d. across each branch?
3.0V
Potential Dividers
V=
R
R Total
×VTotal
What is the p.d. across the
whole of the upper branch?
6.0V
What is the p.d. across the
lower branch?
6.0V
What is the p.d. across each of the
resistors in the upper branch?
3.0V
Potential Dividers
What is the potential at X when the thermistor has a resistance of
1000Ω?
V=
R
R Total
×VTotal
V
1000
 12  11.7V
1030
This is the p.d. across the thermistor, the potential at X is 12-11.7=0.3V
Potential Dividers
What is the potential at X when the LDR has a resistance of 5000Ω?
V=
R
R Total
×VTotal
V
5000
 12  11.9V
5050
This is the p.d. across the LDR, in this case it is also the potential at X due
to where the LDR is in the circuit.
Superconductivity
Certain materials have zero resistivity at and below a
critical temperature which depends on the material.
There is a persistent current in the superconductor that causes a
magnetic field to be set up that repels the magnetic field of the
permanent magnet.
EMF and internal resistance
• The quantity of energy
transferred to unit charge as it
passes through the cell
• The p.d. across the cell when
no current flows
ε  I(R  r)
• Energy is transferred in the
cell due to the internal
resistance
RMS Values
I0
Irms 
 0.707I0
2
V0
Vrms 
 0.707V0
2
Oscilloscope


x-axis is called the timebase
y-axis is the y-gain or input sensitivity (which represents p.d.)
Calculate the frequency
and the amplitude of the
signal shown if the
timebase is set to 10ms /
division and the y-gain is
set at 100mV / division
T=40x10-3s
f=1/T=25Hz
Peak Voltage
= 1.5x100mV
= 150mV