Book Four Flashcards
Electricity - DC circuits - Particle and nuclear physics
what is electric current? +formula
the rate of flow of electric charge past a point in a circuit
Q = It
Current = A
Charge = C
what are charge carriers?
charged particles which contribute to the flow of electric current. (electrons, protons or ions)
elementary charge
1.6 x 10^-19C
what is number density?
the number of conduction electrons per unit volume
what is potential difference?
energy transferred per unit charge from electrical to other forms of energy in a circuit
pd = energy / Q or pd = W / Q
V
what is a volt?
the pd across a conductor whose resistance is one ohm when a current of 1 amp. flows through it
what is power? (electrical power)
the rate if energy transfer
P = E/t or P=W/t
watt
what is ohms law?
current in a metallic conductor is directly proportional to potential difference across its ends provided its temperature remains constant
R = V/I
what is a thermistor?
a resistor whose resistance varies with temperature
cold - high resistance
hot - low resistance
graph - y=tanx shape
what is a light dependent resistor? (LDR)
a resistor whose resistance varies with intensity of light
darkness - high resistance
light - low resistance
graph - constant gradient passing through zero
what is a diode? (rectifier)
an electronic one way switch
reverse bias - high resistance
forward bias - low resistance
graph - right part of a beaker
what is a filament lamp?
an electric lamp with a filament that can withstand temp. high enough to make it produce white light
low temp. - obeys ohms law
high temp. - doesn’t obey ohms law
graph - deceleration (stretched out s)
(summary page)
pg. 15
what is electromotive force?
any form of energy converted into electrical energy per unit charge
E = E / Q or E = W / Q
what is internal resistance?
resistance of materials within a source of power
what is terminal pd?
the pd between the terminals of a cell or a power supply when a current is being delivered
what is maximum power?
the load resistance of the circuit is equal to the internal resistance of the battery
what is kirchoffs 1st law?
the sum of currents entering a junction in a circuit is always equal to sum of current leaving the junction
(conservation of charge)
what is kirchoffs 2nd law?
the sum of emf around any loop in a circuit is equal to sum of pd around the loop
what is a potential divider?
2 fixed resistors connected in series with a cell
equation for resistors in series
V = V1 + V2 + V3
IR = IR1 + IR2 + IR3
R = R1 + R2 + ….. +Rn-1 + Rn
n is the number of resistors
equation for resistors in parallel
I = I1 + I2 + I3
V/R = V/R1 + V/R2 + V/R3
1/R = 1/R1 + 1/R2 + 1/R3
n is the number of resistors
equation for
- 2 resistors in parallel
- 2 resistors are identical
1/R = 1/R1 + 1/R2
1/R = R2+R1/R1R2
R(R2+R1) = R1R2
R1R2 / R1+R2
resistance = product / sum
R = R1/n
n is the number of identical resistors
what is a potentiometer?
a continuously variable potential divider
e.g. a variable resistor (rheostat) may be used as a potentiometer
nb:
page 32, 33 & 34
rutherfords alpha-particle scattering experiment observations and conclusion
- vast majority of α-particles passed straight through the gold foil with virtually no deflection
- atom is mostly empty space - few of the α-particles were deflected through angles greater than 90 degrees
- centre of atom, tiny pos. charged nucleus which contains most of its mass and charge
subatomic particles (proton, neutron, electron)
proton
1u - +e - in nucleus
neutron
1u - 0 - in nucleus
electron
u/1820 - -e - orbiting nucleus
- proton number?
- nucleon number?
- nucleon?
no. of protons in the nucleus of atom
protons+neutrons in nucleus of atom
name given to either proton or neutron
what is an isotope?
atoms of the same element with the same number of protons but different number of neutrons
what is a nuclide?
a single type of nucleus with a specific nucleon number and specific proton
what is radioactivity?
the emission of particles and electromagnetic radiation by unstable nuclei in order to be stable
what is radioactive decay?
spontaneous disintegration of unstable nuclei in order to become stable. emits em radiation
3 different ionising radioactive emission visible to the human eye
alpha-particles, beta-particles, gamma rays
properties of an alpha-particle
- nucleus of a helium atom
- carries a charge +2e
- travels up to 3.0X10^7 ms^-1
- least penetrating of the 3; stopped by thin card
- range in air is just a few cm
- deflected by electric and magnetic fields because of its charge
- most ionising because of its relatively large mass & charge
properties of a beta-particle
- fast moving electron
- has a charge of -1e
- travels at 2.97x10^8 ms^-1
- more penetrating than α, stopped by a few mm of Al
- range in air is about 1m
- deflected by both electric and magnetic fields in opp. way to α-because of its charge
- not as ionising as α because of its relatively small mass and charge
properties of gamma rays
- part of the em spectrum with the greatest energy
- travel at a speed of light 3x10^8 ms^-1
- most penetrating, intensity reduced by several m of concrete or cm of lead
- range in air is unlimited
- have no charge, not deflected by electric or magnetic fields
- have no mass and charge, least ionising of the 3
deflection by a magnetic field of α,γ,β
α - slightly deflected
γ - not deflected
β - heavily deflected
deflection by an electric field
α - deflected slightly towards -ve plate
γ - not deflected
β - deflected heavily towards +ve plate
how to detect radioactivity
- the Geiger-Muller tube (GM tube)
- photographic plates/film
what is background radiation?
sum of all natural and man-made radiation
- granite rocks
- certain foods
- our bodies
- cosmic radiation
uses of radioactivity
- tracers
- radiotherapy
- testing for cracks in metals
- monitoring thickness of sheets of materials
- sterilisation of hospital equipment
- preservation of fruits
- carbon dating
dangers of radiation
- can damage or destroy living cells and stop organs in the body from working properly
- can upset chemical instructions in cells so that they grow abnormally and cause cancer
safety with radioactive source
- stored in lead containers in a locked cabinet
- picked up with tongs, not by hand
- kept well away from the body and pointed away from others
- left out of its container for as short a time as possible
what are fundamental particles?
subatomic particles that are not composed of other particles
families of particles
leptons (light) are not affected by strong nuclear force such as electrons and neutrinos
hadrons (heavy) are affected by the strong nuclear force such as protons and neutrons
leptons
electrons, positrons, neutrinos, antineutrinos, fundamental particles with no further structure
hadrons
protons, neutrons and their antiparticles known as hadrons.
there are different types of hadrons and each type is made up of different combinations of 2 or 3 smaller particles known as quarks
quark flavours
up, down, charm, strange, top and bottom
upness, downness, strangeness
nb:
table on page 47
types of hadrons
baryons - made up of 3 quarks
mesons - made up of 2 quarks
baryons
- they are protons and neutrons
proton, p = uud
neutron, n = udd
mesons
made up of 1 quark and 1 antiquark
what is antimatter?
matter that is made up of antiparticles
what are positrons?
a form of antimatter, anti-electrons
what are neutrinos?
particles with very little mass and no electric charge
nb:
a fundamental particle has no internal structure
