Chapter 8 - Electrostatics and Electromagnetism Flashcards
What are electric field lines? What is their directionality and strength?
They are lines of force representing an electric field. They always originate on a positive charge and end on a negative charge. They represent the way a positive charge would migrate. Field lines close together mean the electric field is strong, whereas field lines farther apart mean the electric field is weak.
What is a test charge (q’)?
an arbitrary positive charge with an electric field
Equation: Faraday’s law of electromotive force
emf = -ΔφB/Δt
φB = magnetic flux
Equation: electric dipole moment
P = qL
q = product of the charge
L = distance separating charges
What is meant by dielectric behavior of a medium?
A strongly polar medium (high K) responds to an external electric field by reorienting its polar molecules so that the net electric field within the medium becomes weaker than the external field. (δ+ charges of the medium align with the negative plate and δ- charges align with the positive plate)
Mass of an electron
9.11 x 10-31 kg
Diagram of electric field
What is the net force on an electric dipole in a uniform electric field?
zero
What are the units of electrical potential energy?
J
Equation: change in electrical potential energy
ΔPEq = kq1q2 (1/rf - 1/ri)
ri = initial separation of charges
rf = final separation of charges
Equation: magnetic field force
Fmagnetic = qvB⊥ = qvBsinθ
v = velocity
B = magnetic field
θ = angle between v and B
Equation: electrical potential difference of a moving charged particle (2 versions)
VAB = ΔPEAB/q
ΔPEq = qV
When a charged particle moves with velocity through a magnetic field, at what position is the magnetic force strongest? Weakest?
velocity perpendicular to magnetic field: greatest force
volecity parallel to magnetic field: smallest force
Equation: electric field
E = F/q = mg/q
What is a conductor?
a material that allows for the movement of a charge
What are equipotential lines? What is their positional relation to field lines?
They are lines that connect all points within an electric field sharing the same potential. They are perpendicular to field lines.
What are the units of electrical potential energy difference?
J/C = volt (V)
What is the unit of an electric field?
N/C
What is an absolute potential?
Voltage measurements at points in space relative to the ground point.
About how much greater is the mass of a proton than the mass of an electron?
~2000
What are the units of magnetic fields?
N•s/C•m or N/A•m = T (tesla)
Diagram of magnetic field
What is Lenz’s law of conducting loops?
As a conducting loop enters a magnetic field, the loop experiences an induced current that creates a magnetic field in the opposite direction. When it is immersed in the field, it experiences no current. When it exits, it again creates a magnetic field, this time opposite the one it made.
Equation: Coulomb’s law of electrical force
F = k (|q1q2|)/r2
k = proportionality constant = 8.99 x 109 N•m2/C2
Equation: torque on a conducting loop within a magnetic field
τ = NIAB sinφ
N = # of turns
I = current
A = area of loop
B = external magnetic field
φ = angle between external field and loop’s field
Charge of an electron
-1.6 x 10-19 C
What is a solenoid?
a helical winding of a conducting wire wound on a cylindrical tube where the length is at least four times its radius
Upon passing current through a solenoid, it can generate a linear magnetic field.
Equation: torque of electric dipole in a uniform electric field (2 versions)
τ = (pE)(sinθ) = (qE)(Lsinθ)
p = dipole
Equation: dielectric constant
K = Fvacuum/Fmedium
Mass of a neutron
1.673 x 10-27 kg
When a test charge moves in the direction of a field line, it moves from higher/lower potential to higher/lower potential?
It moves from higher to lower potential.
How can electrical potential energy between two charges be changed?
If you must do work to move two charges, you have increased their PE (bring two like charges together, pulling opposite charges apart).
If the charges move naturally, they are decreasing their PE (bring two opposite charges together, pulling like charges apart).
When a solenoid generates a mangetic field, what is that field dependent upon?
- current (I) passing through the solenoid
- solenoid dimensions
What is charge conservation?
The total electric charge on two objects in a system does not change. Even though the charge can be transferred from one object to the next, it cannot be created or destroyed.
Charge of a proton
1.6 x 10-19 C
When an electric dipole (p) is introduced into a uniform electric field (E), at which position is its potential energy the greatest? the least?
dipole perpendicular to electric field: zero PE
dipole parallel to electric field: most stable, negative PE
dipole antiparallel to electric field: least stable, positive PE
What are the units of charge?
coulomb (C)
What is an insulator?
a material that impedes the movement of charge
Equation: potential energy of electric dipole in a uniform electric field
PE = - (pEcosθ)
Right-hand rule of magnetic force
thumb = velocity of positively charged particle
fingers = direction of magnetic field
palm = magnetic force
*If particle is negative, the force will be opposite
Right-hand rule for current in magnetic field
Thumb = direction of magnetic field B
Curled fingers = CW/CCW direction of current
Mass of a proton
1.673 x 10-27 kg
How do equipotential lines correlate with work done on a test charge?
If the test charge is placed at any point along an equipotential line, the electric field does no work on that test charge.
Equation: exit speed of a charged particle in a velocity selector
v = E/B
Equation: mass spectrometer radius/mass correlation
r = mv/qB
What is an electrical ground point?
An electrical point of reference with a voltage of 0.
Diagram of symbols for magnetic field into or out of page
When an electric dipole (p) is introduced into a uniform electric field (E), at which position is its torque the greatest? the least?
dipole perpendicular to field = greatest torque
dipole parallel/antiparallel to field = least torque
Equation: electric force in a field
Felectric = qE = mg
Equation: electric work (2 versions)
W = qEΔd = qΔV
Equation: velocity of charged particle in electric field
Vf = √(2qΔV/m)
Equation: force on conducting loop in a magnetic field
F = Il x B
I = current
l = length of loop
B = magnetic field
Do electric fields and magnetic fields have the ability to accelerate a charged particle from rest?
Electric fields can, magnetic fields cannot.
Do electric fields and magnetic fields do work on a charged particle?
Electric fields can, magnetic fields cannot.
