MIDTERM I Flashcards
which way does conventional current flow through a circuit?
from the higher potential to the lower potential (because conventional current involves the flow of positive charges)
what are equipotential SURFACES supposed to depict?
all points perpendicular to the electric field where the electric potentials are equal and particles can move along them without any work being done…???? IN 3D
voltage is…
electric potential PER CHARGE
electric potential is…
the potential energy IN JOULES that a charged particle has/contains d/t its location within an electric field
why/how does friction generate electrical charge?
electrons actually move from one object to another (via conduction), causing imbalances in the objects’ protons and electrons
what are electric field lines supposed to show you?
the direction of a charge’s electric field
what is current?
flowing charge. not the same as static charge
what is capacitance?
the amount of charge a material can hold (which can be calculated, and is r/t physical properties)
wires with currents flowing in the same direction: attracted or repelled?
attract
what is a dielectric?
the non-conducting material (like plastic, paper, or air) that exists between the plates of a capacitor to help keep the charges from traveling across the gap
what are the 2 terms in the electric field eqn?
- force (of particle) WHICH IS A VECTOR
2. charge (of particle)
why/how does friction generate electrical charge?
electrons actually move from one object to another (via conduction or induction), causing imbalances in the objects’ protons and electrons
electric charge of an PROTON is…
1.6E19 coulombs
who can you tell which part of a magnet is its north pole?
the north pole is the part that points toward geographic north when placed
what are root mean square (rms) values for quantities involved in alternating current calculations?
the square roots of the average values for a given quantity (i.e. the square root of the average current for a given system)
which of these terms does NOT have an rms value: current, resistance, or voltage?
resistance
what does the energy density of a capacitor describe?
the volume of energy a capacitor can store
energy per unit volume
what is the dielectric constant (k) for air?
1
what are the 4 terms in the eqn for the MAGNITUDE of magnetic force exerted ON a wire, BY a nearby current?
- the radius
- 2(pi)
- the current (I)
- ‘permeability’ of free space constant (mu naught)
electric potential DIFFERENCE (aka voltage DIFFERENCE) can be describe as…
the amount of energy/work required to move a ONE COULOMB OF CHARGE from one location within in electric field to another (given) location within the electric field
what is a battery?
a device whose voltage/electric potential facilitates current in a circuit
the battery contains positive and negative charges that can’t get to one another until/unless you provide the pathway/circuit for them to travel through
what is a magnet?
a material that attracts ‘ferromagnetic’ materials and creates a magnetic field
what are the 3 terms in the wire resistance eqn (the one that includes resistivity constant)?
- L for length of wire
- A for area (of the cross section of) wire
- resistivity or the material
electric potential is a type of…
potential energy
what do electric dipoles have to do with equipotential lines/surfaces?
equal and opposite equipotential lines/surfaces of separate particles give rise to electric dipoles
how many different ways are there to write the power eqn (involving voltage and current)?
3
what does the resistivity of a material tell you?
the amount of resistance the material has; this is a property of the material that you get from a table
what are the 3 ways an object can become charged?
- friction (touching)
- conduction (touching)
- induction (NO touching)
which way do electric field/lines travel for NEGATIVE charges?
radially TOWARDS/into the particle
what is a watt?
power per time
how many joules is 1 eVolt?
1.6E-19 joules
how does resistance related to current and voltage in the Ohm’s Law eqn?
R = V/I because R follows from physical properties of a material, regardless of the voltage being introduced
what are the 4 terms in the eqn for the MAGNITUDE of two wires’ currents exerting magnetic fields on one another?
- the radius
- 2(pi)
- the current (I)
- ‘permeability’ of free space constant (mu naught)
what are equipotential lines supposed to depict?
all points perpendicular to the electric field where the electric potentials are equal and particles can move along them without any work being done…???? IN 2D
electric charge of an electron is…
-1.6E19 coulombs
what is voltage difference?
what you call it when the voltage (energy/charge) in one location of an electric field is different from the voltage in another location of the electric field
what is the mass of an electron?
9.11E-31 kg
is voltage (in a circuit) considered constant?
yes (until/unless the battery dies)
electric INSULATORS are…
materials that ONLY A FEW free electrons can flow freely through
how is current related to resistance in Ohm’s Law eqn?
current goes down as resistance goes up
resistance impedes the flow of current
what are the units for electric potential?
Joules
activity starting with the letter f that causes/generates charge
friction
what are the units for voltage?
joules/coulombs
what is a kWh?
1000 * number of what’s * elapsed time IN HOURS!!!
what is a Tesla the unit for?
the MAGNITUDE of the force exerted by a magnetic field
what is peak current (as it r/t alternating current)?
The amplitude/(highest positive) CURRENT value (as shown on a sinusoidal waveform graph) for a system
Called I naught
how many joules does 1 kWh convert to?
3.6E6 joules
what is the difference between CONduction and INDuction
in CONduction, objects are touching, and electrons are actually transferred.
in INduction, objects are NOT touching, so electrons aren’t transferred, but they reorient themselves (in place) towards or away from the charge of the other object
what is drift speed?
average speed of electrons in a system using ALTERNATING CURRENT
what is peak voltage (as it r/t alternating current)?
The amplitude/(highest positive) voltage value (as shown on a sinusoidal waveform graph) for a system
Called V naught
voltage gives rise to…
current/flow of CHARGE
what are the 2 terms in the MAGNITUDE of the electric field eqn?
- charge
2. radius squared
Can an electric field occur with both static charges AND flowing charges/current?
yes
what are the units for an electric field?
force per charge;
newtons/coulombs (N/C)
why bother with root mean square (rms) values for quantities involved in alternating current calculations?
they can more easily be plugged into the 3 versions of the power eqn
electric conductors are…
materials that free electrons can flow freely through
what version of power can you solve for (using peak values) in alternating current problems?
average power
electric potential: scalar or vector?
scalar
if you need to add/subtract them, don’t bother decomposing anything
what are the units for capacitance?
Farads C^2/N*m
aka charge per voltage (C/V)
why are ‘voltage’ and ‘electric potential’ used interchangeably?
fuck if I know…
voltage difference is also called…
electric potential DIFFERENCE
if you have to add a bunch of forces to find the VECTOR of an electric field, what 4 things do you have to do?
- plug the given numbers into the E field eqn to calculate a RESULTANT/magnitude of the field
- Decompose the vectors
- Add the vectors, paying attention to SIGNS!!!
- Use pythagorean theorem to determine the DIRECTION of the E field
what are the 4 terms in the eqn for the MAGNITUDE of magnetic force exerted on a current IN A WIRE
- current (I)
- length of wire (l)
- magnitude of magnetic field (B)
- sine of the angle between the magnetic field and the current (sin theta)
what is a capacitor?
a material/device that stores CHARGE (and electric/potential energy)
what units do kWh convert to?
joules!
what happens to electric potential (d/t electric dipoles) as the distance between the 2 particles involved increases?
the electric potential decreases by 1/r2 where r is the radius between particles
what are the 2 types of electric charge
postive and negative
what is the MAGNITUDE version of the electric field eqn used for?
giving you the magnitude of the electric field at any point in space, not just the specific location of a given test point
which way do electric field/lines travel for positive charges?
radially AWAY FROM/out of the particle
what does 1 Telsa convert to?
N/A*m
units for electric charge are…
Coulombs (C)
what is the capacitance constant (bka permittivity of free space)?
8.85E-12 C^2/N*m^2
what do eVolts convert to?
Joules! not volts!
what are the unites for electric potential DIFFERENCE
JOULES
electric charge is primarily carried by…
electrons
what are the 4 terms in the eqn for the MAGNITUDE of magnetic force exerted on a SINGLE CHARGE within a current?
- charge of test point (q)
- velocity of test point (v)
- magnitude of magnetic field (B)
- sine of the angle between the magnetic field and the test point’s velocity (sin theta)
what does the ‘permeability of free space’ constant equal (in the current/wire caused magnetic field eqn) equal?
4 pi E-7 T*m/A
how/when is it possible for a charge’s electric field to be going in a different direction from its force?
If the charge is positive (e field pointing out) but the other charge has the same sign
If the charge is negative (e field pointing in) but the other charge has an OPPOSITE sign
word starting with the letter q that describes electrical charges
quantized
Per Coulomb’s Law: what are the 4 terms in the equation for magnitude of force that one charge/test point exerts on another?
- k constant
- charge of first particle
- charge of other particle
- radius between particles
Per Coulomb’s Law: what are the 4 terms in the equation for magnitude of force that one charge/test point exerts on another?
- k constant
- charge of first particle
- charge of other particle
- radius squared between particles
what is power?
the amount of energy that gets transformed from one form (like potential energy) to another form (like kinetic energy) within a system (like a transformer)
electric charge
property that gives rise to a particle’s ability to attract or repel other particles without actually touching them
what is the mass of a proton?
1.67E-27 kg
what are capacitors usually composed of?
2 NON TOUCHING conducting materials (like metal plates) that hold equal & opposite charges (Q), and have a voltage difference/electric potential difference (V) between them
wires with currents flowing in OPPOSITE directionS: attracted or repelled?
REPEL
what is a magnetic field?
a region around a magnet or current that exerts a force on other magnets or other currents
what are the 2 terms in the VECTOR version of the electric field eqn?
- force (of particle) WHICH IS A VECTOR
2. charge (of particle)
