Term 1 Revision Flashcards
Newton’s Laws of Motion
Law 1: An object remains at rest or in uniform motion until an external force acts upon it
Law 2: Force is equal to change in momentum per change in time. For constant mass F=ma
Law 3: For every action there is an equal and opposite reaction
Work done formula
Work done= Force x Distance moved in direction of force
Equation involving Power, work done and time
Power=Work done/time
Working out accelerationm velocity and distance using calculus
a=dv/dt
v=dx/dt
Coulombs law equation (two point charges) involving force, charges and distance
F=(1/4πε0) * (q1q2/r)
ε0=permitivity of free space
q=charges of points
r=DISTANCE (not radius)
Electric field (force exerted due to a point charge) equation involving electric field, charge and distance
E=(1/4π*ε0) *(q/r^2)
E=electric field
q=charge
r=DISTANCE (not radius)
Electric potential (work done in moving unit positive charge from infintiy (zero potential) to a point) equation involving work done, force and distance
Work done=F*X
X=distance moved in direction of force
Integral and differential equations for electric potential
E=-dV/dx
V=-∫ E dx (integrating between position ‘a’ and position ‘b’)
V=electric potential
E=electric field
Potential energy in an electric field
Equation involving PE, charge and
Electric potential
P.E=qV
Principle of Superposition
For a general system of charges, total electric field and electric potential can be found by adding up individual electric fields and potentials from each individual charge.
Basically just add up each particle individually
Adding fields and potentials from point charges
Revise this
How do multiple charges generate a uniform electric field between two plates?
Each charge produces a field, these fields add together (superpose). Provided the cross sectional area of the plates is way bigger than the distance between them, the horizontal components of the charges will cancel out (except at the edges. Remember the weird boy girl seat metaphor?)
Calculating force and acceleration of an electron in an electric field
Use F=qE and then F=ma
Definition of current
Rate of flow of charge
I=dQ/dt
If current is uniform take out the d’s to get the formula
Definition of current density
Rate of flow of charge per unit area
J=I/A
A=cross sectional area
Two equations involving current, current density electron charge, number density, area and velocity
I=enAv
J=env
Calculating average drift velocity of electrons in an electric field involving electron charge, electric field, mass of electron and mean time between collisions
V=(eE/m)*τ e=electron charge E=electric field m=mass of electron τ=mean time between collisions
Drift mobility definition and equation (two ways of writing it) involving drift velocity, electric field, electron charge, mean time and mass of electron
Avergae drift velocity acquired per unit electric field. μ=V/E=eτ/m V=drift velocity E=electric field e=electron charge τ=mean time between collisions m=mass of electron
How does drift mobility actually mean and what does it say about conductivity?
Reflects how fast carriers will drift in an applied electric field.
If mean time between collisions is large, mobility and velocity will be large and vice versa.
Mobility reflects sample quality but dosn’t necessarily mean a high conductivity, since that depends on number of carriers
Conductivity definition and equation-both how you calculate it and its relation to current density. Involves number density, electron charge, mobility
The degree to which a material conducts electricity. σ=neμ n=number density e=electron charge μ=mobility
J=σE
J=currenty density
E=electric field
Deriving Ohm’s law from J=σE
J=σE J=I/A E=V/L Therefore I/A=σV/L Rearrange to get V=(L/Aσ)*I As R=L/Aσ, V=IR
Definition of diffusion current and symbol
Symbol for diffusion current density
Current caused by diffusion of charge carriers (carriers moving from high concentration to low concentration)
Symbol is Γ
Symbol is Jdif (dif in subscript)
Covalent bonding definition and properties
When two non-metal atoms share electrons from their outer shells.
High melting point, very hard but brittle
Insoluable and poor conductivity
Metallic bonding definition and properties
As metals have few electrons in their outer shells, bonding involves multiple ions sharing electrons in a ‘cloud’.
High ductility (easy to manipulate)
High electrical conductivity
High thermal conductivity
Ionic bonding definition and properties
Happens between metal and non-metal. The metal loses an electron to the non-metal. This makes the metal positive which attracts it to the newly negativly charged non-metal.
Strong, brittle, high melting points compared to metals
Mostly soluable
Electric insulator (no free electrons)
Poor thermal conductivity
Crystal, lattice, basis: definition
Three-dimensional periodic arrangement of atoms
Imaginary array of geometric points
Set of atoms which is placed at each lattice point
Maxwell’s right hand rule
Point thumb in direction of current and make a fist. Your fingers are pointing in the direction of the magnetic field
Left rule for force on a conductor
Make a gun with left hand. FBI F=force, thumb B=magnetic field, second finger I=current, third finger
Equation involving force, magnetic field, current, angle of conductor and length of conductor
F=BILsin(α) F=force B=magnetic field I=current L=length of conductor α=angle
Equation involving force, magnetic field, charge of particle and speed of particle
F=Bqv F=force B=magnetic field q=charge of particle v=speed of particle
Explain the Hall Effect
When a current flows through a material in a perpendicular magnetic field, electrons experience a force at right angles to their motion.
Electrons then build up on one side, creating a positive charge on the other.
This creates a force which attracts electrons towards it.
A voltage (Hall voltage) can be measured between the sides
Lenz’s law definition
The induced current flows always in such a direction as to oppose the change causing it
Equation for induced emf and flux involving induced emf, flux, time, area, magnetic field and angle between normal of area and magnetic field direction
v=-dΦ/dt Φ=AB*cos(θ) V=induced emf Φ=flux t=time A=area B=magnetic field θ=angle
Faraday’s law
Any change in the magnetic environment of a coil of wire will cause a voltage (emf) to be “induced” in the coil
v=-dΦ/dt
Dynamo definition and formula for induced voltage in dynamo involving flux, number of loops in wire, area, magnetic field and angle
Used to convert movement into an alternating current
Φ=NABcos(θ)
Φ=flux
N=number of loops in wire
A=area
B=magnetic field
θ=angle between normal of coil and normal of magnetic field
Transformer definition and equations for flux in each coil involving flux, number of turns, area and magnetic field
Coils of wire used to step up or down an AC voltage Consists of primary and secondary coils Φp=NpAB Φs=NsAB Φ=flux(primary/secondary coil) N=number of turns A=area B=magnetic field
Relation between induced emf in transformer coils and number of turns in transformer coils
Vp/Vs=Np/Ns
V=induced emf (primary/secondary)
N=number of turns
Motor definition
A motor is a dynamo with power connected to it. It converts AC current into movement
Back emf definition
As the motor turns there is a changing flux which creates a voltage (Faraday’s law) and the direction opposes the motion. Hence the induced emf counteracts the applied voltage from the battery
Self inductance definition
The inductance of a voltage in a current-carrying wire when the current is changing (inductance is when a magnetic field is created by an electrical current)
Formula for self inductance involving back emf and rate of change of current.
Unit of self inductance
Relating self inductance to flux in one nice formula
Self inductance (L) = Back-emf induced in a coil by a changing current/rate of change of current through the coil Unit is the Henry (H) L=Φ/I Φ=flux linkage I=current
Mutual inductance (like in a transformer)
Occurs if there is a change in flux in one circuit owing to change in current in another
M=Φb/Ia=Φa/Ib
Φ=flux in each circut
I=current in each circuit
Dielectric definition and formula for dielectric constant
Materials placed between capacitor plates to increase both capacitance and insulating behaviour. This is due to the dielectric reducing the electric field between the plates. Q/Q0=C/C0=εr Q=charge between places C=capacitance 0=state before dielectric was inserted
Polarisation definition and formula for electric dipole moment
Occurs in a medium when positive and negative charges are displaced from where they are normally.
An atom is polarised if there’s a seperation between positive and negative charges
Can also be described as total dipole moment per unit volume
P=nPav
P=polarisation
n=number of molecules per unit volume
Pav=average dipole moment of an individual molecule
a=seperation of charges
Electric dipole moment, induced dipole moment definitions and formulas
Measure of the seperation between positive and negative charges. Induced if the atom has been induced to become a dipole. P=αE α=polarisability of atom E=electric field p=Qa p=dipole moment Q=charge of particles
When to use SHM equations?
SHM displacement equations involving displacement, two constants, angular frequency time and triginometric functions.
How do we get velocity and acceleration from these equations?
When force on an object isn't constant x=Acos(wt) x=Bsin(wt) x=displacement A,B=constants w=angular frequency t=time
DIfferentiate once to get velocity, again to get acceleration
Whats the link between SHM and dipole moments?
When an electric field is applied positive and negative charges will seperate. But when the field is removed, the charges will be pulled back towards each other. They will then osscilate under SHM until they stabilise
Diamagnetic and paramagnetic-where are they attracted to in magnetic fields?
Diamagetic materials are repelled by fields due to small and negative susceptibility
Paramagnetic materials are attracted by fields due to small and positive susceptibility
Ferromagnetic materials
Materials like iron which possess large magnetic moments even without an applied magnetic field
Susceptibility is usually positive and very large
What is atomic packing factor?
Volume of atoms/total volume
