Transcript NewAS Revision Unit 1

AS REVISION UNIT 1
TOPIC : PARTICLES, QUANTUM
PHENOMENA AND ELECTRICITY
Explain what is meant by an
electric current.
An electric current consists of a
flow of electrons.
What is the difference
between “conventional
current” and the an “electron
flow current”?
Conventional current flow from
positive to negative, electron flow
current flows from negative to
positive.
Define the Volt
This is the p.d. when the work
done of 1J when 1 coulomb of
charge flows.
Define the Ohm
The Ohm is the resistance when 1
volt is applied when a current of 1
ampere flows.
Explain the meaning of
resistance.
Resistance is the opposition to
flow of an electric current.
Explain the origin of resistance
in a conductor.
The atoms in the conductor form
the basis of opposition to the flow
of current.
State the three formulas for
power
P = I.V ,
P = V2 /R ,
P = I2 R.
Define the term resistivity
Resistivity is the resistance in a
unit cross-sectional area per unit
length.
State two factors that affect
the resistance of a material
Length, cross-sectional area,
material and temperature of the
material.
State Ohm’s Law
The p.d. across a conductor is
proportional to the current flowing
through it, provided the
temperature remains constant.
Describe what happens to the resistance
of a thermistor when it is heated.
As the temperature of the
thermistor increases its
resistance decreases.
What is a kilowatt-hour?
A kilowatt-hour is the energy an
appliance of 1kW used in one
hour.
IkWh = 3.6 x 106 J
What happens to the
resistance of a material if the
length doubles?
The resistance doubles .
What happens to the
resistance of a material if the
cross-sectional area doubles?
The resistance halves.
What happens to the
resistance if the diameter of a
wire doubles?
The resistance decreases by a
factor of 4.
Since doubling the diameter
increases the area by a factor of
four.
Define Resistance
Ratio of the p.d. across a
conductor to the current through
it.
Can resistivity change with
temperature?
Yes, the resistivity increases with
temperature.
Does a filament bulb obey
Ohm’s Law?
No, the resistance changes due to
a change in temperature.
Does a diode obey Ohm’s
Law?
No, the resistance changes due to
a change in charge carriers.
State a formula for the work
done in a circuit.
W = VxIxt
V = P.D.,
I = Current in
amp
t = time in
seconds
How is power related to work?
Power = Work Done / Time Taken
What is the meaning of
electric charge?
Electric charge is a quantity of
electricity on charged particles.
Why does an electric current
move slowly?
An electric current consists of free
electrons moving superimposed
on random motion of electrons
Define the term potential
difference.
Potential difference is defined as
the work done per unit charge in
converting electrical energy into
other forms
Define the term resistivity.
Resistivity is defined as the
resistance of a conductor in a unit
cross-sectional area per unit
length.
Define Electromotive Force
Work done per unit charge in
converting the source energy into
electrical energy in a circuit.
How is emf different from
p.d.?
Emf is the energy per unit charge
in converting energy in a circuit.
P.d in energy/charge converted
across a component.
How is charge conserved in a
circuit?
In any closed circuit the amount
of charge flowing is constant, the
rate of flow of charge is constant.
Explain how energy is
conserved in a circuit.
In any circuit the energy supplied
by the source is dissipated in the
components.
State the formulas for the sum
of three resistors in parallel.
1/RT = 1/R1 + 1/R2 + 1/R3
For 2 resistors RT = Product/Sum
State the formulas for the sum
of three resistors in series.
. RT = R1 + R2 + R3
What is the purpose of a
potential divider?
A potential divider gives a
proportion of the source potential
to another circuit.
What is meant by an ‘open
circuit’?
It is a circuit where a current does
not flow.
Sketch the Current-Voltage
curve for a Resistor.
Sketch the Current-Voltage
curve for a Lamp.
Sketch the Current-Voltage curve
for a diode.
What is meant by a closed circuit?
• It is a circuit where a current flow
What is meant by the terminal
pd? State a formula in terms
of the emf and the internal
resistance.
Terminal p.d. is the pd across the
terminals of a cell.
IR = E - Ir
Explain why the pd across a
cell drops when a resistor is
connected to a cell.
P.d. is dropped across the internal
resistance which reduces the
terminal pd. from the formula,
IR = E -Ir
How is a voltmeter connected
in a circuit? Why is the
resistance of a voltmeter
high?
In parallel.
The resistance is high so no
current flows through it.
How is an ammeter connected
in a circuit?
Why is the resistance of a
ammeter low?
In series.
So that it take all the current and
it does not change the current in
a circuit.
What is the purpose of a
potential divider?
A potential divider gives a
proportion of the source potential
to another circuit.
State the purpose of a wave
To carry and transfer energy.
What is the photoelectric
effect?
Emission of electrons off the
surface of a metal using light.
How can the the photoelectric
effect be demonstrated?
Using a gold leaf electroscope
which is negatively charged, a
clean piece of zinc and a uv lamp.
The leaf slowly collapses as uv
light is shown onto the zinc plate.
What is meant by the
threshold frequency?
Smallest frequency of light
required for electron emission.
What is the work function?
Smallest energy of light photons
required for electron emission.
What is Einstein’s
Photoelectric equation.
hf =  + ½ mv2
max
hf = incident photon energy  =
work function
½ mv2 max = Max ke of
photoelectrons
Explain why the photoelectric
current is proportional to the
intensity of the
electromagnetic radiation.
The greater intensity of the
incident radiation (i.e more
photon hitting the metal surface)
the number of electrons emitted
per second.
Explain what is meant by a
photon of electromagnetic
radiation .
This is a packet or quantum of
energy.
State the formula that relates
the energy of a photon to the
frequency of electromagnetic
radiation. Identify each
symbol.
E = h.f
h = Planck’s Constant
f = frequency of photon
Why is the energy of each
electron different?
Each electron could originate from
different depths within the metal
surface.
What does the photoelectric
effect show?
It shows that light has a
particle nature.
State two effects that show
light has a wave nature?
Diffraction and interference.
Define the electron-volt.
Energy acquired by an electron
when accelerated by a pd of 1V.
State the order of the
Electromagnetic Spectrum
starting from the smallest
wavelength.
Gamma Rays, X-Rays, Ultraviolet,
Visible Light, Infra Red
Microwaves, Radio Waves
State three common features
of the e-m spectrum.
All transfer energy.
All travel by transverse wave
motion.
All move at the speed of light in a
vacuum.
State two difference of the em spectrum
Different frequencies/wavelengths
Different methods of production
State the evidence that electrons
can behave as waves.
Electrons can show a diffraction
pattern when accelerates through
a fine hole in an evacuated tube.
What is meant by the terms
Excitation and Ionisation?
Excitation occurs when an
electron or atom gains energy and
moves to a higher excited state.
Ionisation occurs when an
electron gains sufficient energy to
escape the atom.
State what a line spectrum in an
atom shows.
A line spectra is evidence for the discrete
energy levels in atoms. The energy emitted
when an electron moves between levels is
given by:
E1 – E2 = h.f
What is meant by proton
number, nucleon number and
specific charge?
Proton Number Z is the number of
protons in the nucleus.
The Nucleon or Mass Number A is
the total number of protons and
neutron in the nucleus.
The Specific Charge is the ratio of
charge to mass for an particle or
ion in C/kg
Explain the reason for the
Nuclear strong Force and given
some properties
The nuclear strong force is the
force which is greater than the
electrostatic repulsion force in the
nucleus.
It is an attractive force of short
range 3fm.
It is repulsive below 0.5fm.
It is independent of charge.
State the general equation for
alpha decay
State the equation for beta
decay
What is meant by an
antiparticle?
An antiparticle is a particle which
has the same mass as its particle
but with opposite properties e.g.
spin
What is an annihilation
reaction?
This a reaction where a particle
and its antiparticle combine with
the emission of energy.E.g.
Electron and positron.
+
-
What is the meaning of pair
production?
Pair production occurs when a
photon interacts with matter to
produce a particle and
antiparticle.
What is the exchange particle
between elementary particles
e.g. electrons?
Photons.
What are the exchange particles
in beta decay and in electron
capture reactions?
W+ , W- bosons.
What are Hadrons?
Hadrons are particles which are
subjected to the strong nuclear
force.
There are two types, Baryons e.g.
protons and neutrons and
Mesons.
What are Leptons?
Leptons are particles which are
subjected to weak interactions.
Examples of leptons are electrons
and neutrinos.
What is the baryon number for
protons, antiprotons, neutrons,
antineutrons and mesons?
Protons and neutrons 1
Antiprotons and antineutrons -1
Mesons e.g. pions
0
Draw the Feynman diagram
for electron-proton collision.
Draw the Feynman diagram
for electron-proton collision.
Draw the Feynman diagram
for beta-minus decay.
Draw the Feynman diagram
for beta plus decay.
State three types of quarks
Up, down, and strange.
(Top, bottom, and charm)
State quarks are in a proton.
Up, up and down quarks
State the quarks in a neutron
Down, down and up quarks
What is the change in quark in
beta minus decay?
In β- decay a down quark
changes to an up quark.
What is the change in quark in
beta plus decay?
In β+ decay an up quark in a
proton changes to a down quark.
In any collision or decay what
laws should be obeyed?
Lepton number
Baryon number
Charge
Strangeness.