Term 1 Revision

Question 1

Newton’s Laws of Motion

Answer 1

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

Question 2

Work done formula

Answer 2

Work done= Force x Distance moved in direction of force

Question 3

Equation involving Power, work done and time

Answer 3

Power=Work done/time

Question 4

Working out accelerationm velocity and distance using calculus

Answer 4

a=dv/dt

v=dx/dt

Question 5

Coulombs law equation (two point charges) involving force, charges and distance

Answer 5

F=(1/4πε0) * (q1q2/r)
ε0=permitivity of free space
q=charges of points
r=DISTANCE (not radius)

Question 6

Electric field (force exerted due to a point charge) equation involving electric field, charge and distance

Answer 6

E=(1/4π*ε0) *(q/r^2)
E=electric field
q=charge
r=DISTANCE (not radius)

Question 7

Electric potential (work done in moving unit positive charge from infintiy (zero potential) to a point) equation involving work done, force and distance

Answer 7

Work done=F*X

X=distance moved in direction of force

Question 8

Integral and differential equations for electric potential

Answer 8

E=-dV/dx
V=-∫ E dx (integrating between position ‘a’ and position ‘b’)
V=electric potential
E=electric field

Question 9

Potential energy in an electric field
Equation involving PE, charge and
Electric potential

Answer 9

P.E=qV

Question 10

Principle of Superposition

Answer 10

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

Question 11

Adding fields and potentials from point charges

Answer 11

Revise this

Question 12

How do multiple charges generate a uniform electric field between two plates?

Answer 12

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?)

Question 13

Calculating force and acceleration of an electron in an electric field

Answer 13

Use F=qE and then F=ma

Question 14

Definition of current

Answer 14

Rate of flow of charge
I=dQ/dt
If current is uniform take out the d’s to get the formula

Question 15

Definition of current density

Answer 15

Rate of flow of charge per unit area
J=I/A
A=cross sectional area

Question 16

Two equations involving current, current density electron charge, number density, area and velocity

Answer 16

I=enAv

J=env

Question 17

Calculating average drift velocity of electrons in an electric field involving electron charge, electric field, mass of electron and mean time between collisions

Answer 17

V=(eE/m)*τ
e=electron charge
E=electric field
m=mass of electron
τ=mean time between collisions

Question 18

Drift mobility definition and equation (two ways of writing it) involving drift velocity, electric field, electron charge, mean time and mass of electron

Answer 18

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

Question 19

How does drift mobility actually mean and what does it say about conductivity?

Answer 19

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

Question 20

Conductivity definition and equation-both how you calculate it and its relation to current density. Involves number density, electron charge, mobility

Answer 20

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

Question 21

Deriving Ohm’s law from J=σE

Answer 21

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

Question 22

Definition of diffusion current and symbol

Symbol for diffusion current density

Answer 22

Current caused by diffusion of charge carriers (carriers moving from high concentration to low concentration)
Symbol is Γ

Symbol is Jdif (dif in subscript)

Question 23

Covalent bonding definition and properties

Answer 23

When two non-metal atoms share electrons from their outer shells.
High melting point, very hard but brittle
Insoluable and poor conductivity

Question 24

Metallic bonding definition and properties

Answer 24

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

Question 25

Ionic bonding definition and properties

Answer 25

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

Question 26

Crystal, lattice, basis: definition

Answer 26

Three-dimensional periodic arrangement of atoms Imaginary array of geometric points Set of atoms which is placed at each lattice point

Question 27

Maxwell's right hand rule

Answer 27

Point thumb in direction of current and make a fist. Your fingers are pointing in the direction of the magnetic field

Question 28

Left rule for force on a conductor

Answer 28

``` Make a gun with left hand. FBI F=force, thumb B=magnetic field, second finger I=current, third finger ```

Question 29

Equation involving force, magnetic field, current, angle of conductor and length of conductor

Answer 29

``` F=BILsin(α) F=force B=magnetic field I=current L=length of conductor α=angle ```

Question 30

Equation involving force, magnetic field, charge of particle and speed of particle

Answer 30

``` F=Bqv F=force B=magnetic field q=charge of particle v=speed of particle ```

Question 31

Explain the Hall Effect

Answer 31

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

Question 32

Lenz's law definition

Answer 32

The induced current flows always in such a direction as to oppose the change causing it

Question 33

Equation for induced emf and flux involving induced emf, flux, time, area, magnetic field and angle between normal of area and magnetic field direction

Answer 33

``` v=-dΦ/dt Φ=AB*cos(θ) V=induced emf Φ=flux t=time A=area B=magnetic field θ=angle ```

Question 34

Faraday's law

Answer 34

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

Question 35

Dynamo definition and formula for induced voltage in dynamo involving flux, number of loops in wire, area, magnetic field and angle

Answer 35

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

Question 36

Transformer definition and equations for flux in each coil involving flux, number of turns, area and magnetic field

Answer 36

``` 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 ```

Question 37

Relation between induced emf in transformer coils and number of turns in transformer coils

Answer 37

Vp/Vs=Np/Ns V=induced emf (primary/secondary) N=number of turns

Question 38

Motor definition

Answer 38

A motor is a dynamo with power connected to it. It converts AC current into movement

Question 39

Back emf definition

Answer 39

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

Question 40

Self inductance definition

Answer 40

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)

Question 41

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

Answer 41

``` 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 ```

Question 42

Mutual inductance (like in a transformer)

Answer 42

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

Question 43

Dielectric definition and formula for dielectric constant

Answer 43

``` 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 ```

Question 44

Polarisation definition and formula for electric dipole moment

Answer 44

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

Question 45

Electric dipole moment, induced dipole moment definitions and formulas

Answer 45

``` 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 ```

Question 46

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?

Answer 46

``` 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

Question 47

Whats the link between SHM and dipole moments?

Answer 47

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

Question 48

Diamagnetic and paramagnetic-where are they attracted to in magnetic fields?

Answer 48

Diamagetic materials are repelled by fields due to small and negative susceptibility Paramagnetic materials are attracted by fields due to small and positive susceptibility

Question 49

Ferromagnetic materials

Answer 49

Materials like iron which possess large magnetic moments even without an applied magnetic field Susceptibility is usually positive and very large

Question 50

What is atomic packing factor?

Answer 50

Volume of atoms/total volume