MATS_16302: Functional Properties Flashcards
‘piezo’ is the Greek word for what?
Stress
The production of electric current in a material which undergoes mechanical stress is known as?
Piezoelectricity
What is polarisation?
The formula! (in words :-)
Polarisation is the number of dipole moments per volume of a material
True or False:
Polarisation depends on the movement of charges
True
The dielectric constant (κ) is also known as?
Relative permittivity (εr)
Use an equation to express the dielectric constant as a ratio
κ = εr = ε/ε0
where ε is the permittivity of a given material
Give the equation relating polarisation to electric field
P = ε0 x χe x E
Where χe is the
How are dipoles generated?
When there is a displacement of charges in a non-conducting material from their equilibrium positions when an electric field is applied across it
What is the formula for dipole moment (p)?
p = q x a
Where q is the quantity of charge and a is ??
True or False:
A turning moment is generated when an electric field is applied at an angle to a dipole
True
Give the formula for torque when an electric field is applied at an angle to a dipole
T = qEa sinθ
where a is the distance between the positive and negative charge in a dipole
qE = F
What is capacitance?
The amount of charge stored per unit potential difference on the parallel conducting plates of a capacitor
Give three forms of the formula for capacitance
Q/V = (ε A)/d = (1+χe) ε0A /d
How does increasing frequency affect orientation polarisation?
It has no effect up to a point after which higher frequencies reduces it
This lowers the permittivity of the material
What is electric potential?
The work done in moving a positive point charge from infinity to a region within an electric field at a distance r
What is the value for the permittivity of free space (ε0)?
8.85 x 10-12 C2N-1m-2
Give the formula for electric field (E)
E = (1/4πε0) x q/r2
In what direction do the electric field lines point for a negative point charge? Inwards or outwards?
Inwards
In what direction do the electric field lines point for a positive point charge? Inwards or outwards?
Outwards
Write the formula for Coulombic force
F = (1/4πε0) x q1q2/r2
Write the formula for Coulombic force in vector form
F = (1/4πε0) x q1q2r12/r3
where r12 is the vector connecting the point charges and r is the absolute displacement
Where is the centre of mass in a tetrahedron?
0.25 of the height
Measured for the centre of the base face to the apex
Write the formula for an infinitesimal change in work done when a point charge is moved through an electric field
dW = F * dS = qE * ds = q(|E||ds|cos θ)
E and ds are vector quantities and dW (and W in general) is a scalar, hence can be expressed as the dot product of the two vectors
The Drude model is based on what pre-existing theory?
The Kinetic Theory of Gases
What does n stand for in this course?
Number density
The amount of dipoles (N) in a given volume (V)
1 angstrom (1 Å) is how many meters?
1 x 10-10 m
ALWAYS remember to convert to meters!!
State the equation for microscopic Ohm’s law
J = σE
Where J = Current density
σ = Conductivity
E = Electric field
What are the two units of conductivity?
Ω-1m-1
or
Sm-1
where the latter is Siemens per meter
True or False:
Conductivity is the inverse of resistivity
True
What is the Boltzmann constant?
1.38 x 10-23 J/K
What is the value of ℏ?
h/2π
