Electricity And Magnetism Flashcards
We define Electric current (I) as the rate of flow of net charges through a selected area in a unit of time
I = Q / t
Electric current (I) is: a scalar or vector
scalar
SI unit (measurement) of Electric current (I) :
ampere
One ampere =
one coulomb per second
Electrons rapidly collide with ions, even with the absence of the Electric Field (E).
In metals and other conductors
In a conductor, an electron with a charge (q) acquiring extra kinetic energy due to work of the external force (F) of the electric field (E).
F = qE
Voltage (V) between two points is defined as electric field (E) times the displacement ( lower case L ) between these two points.
V = E l
Voltage is a: scalar or vector
Scalar
SI unit (measurement) of voltage:
Volt
Volt =
Walt over ampere (W/A)
Batteries are common sources of:
fixed voltage &
relatively constant voltage.
Power outlets are sources of:
oscillating voltage
The proportionality of the electric current inside a conductor to the electric field is expressed in Ohm’s Law:
V = I R
V = I R
(V) voltage applied to the piece of conductor (such as wire)
(I) electric current through the conductor
(R) electric resistance of the piece of material
Electric resistance (R) - being a ratio of two scalars- is :
scalar
The SI unit (measurement) of Electric resistance (R)
Ohm
Ohm =
Volt over ampere (V/A)
Kirchoff’s laws for electric circuits:
Loop rule: Voltage drop across a closed circuit loop is zero. ( V - IR = 0 )
Branch rule: Net current into a single circuit branch is zero. ( I = I1 + I2 )
Using Kirchoff’s law and Ohm’s law it is easy to derive total resistance of a circuit for resistors in series and resistors in parallel.
( R = R1 + R2 + R3 ) resistors in series
1/R = 1/R1 + 1/R2 + 1/R3
In many conductors, the current is proportional to:
The applied electric field (E) (and voltage)
A simple example of an electric current is:
an incandescent lamp
Measures resistance to the flow of electricity:
Ohm
Voltage source that converts chemical energy to electrical energy:
Battery
The unit and symbol for current
Ampere, I
Something that allows electricity to pass through it:
Electrical conductor
Magnets exert magnet force on:
Iron objects
Magnetic forces originate from:
moving electric charges
Elementary particles like electrons:
behave like little magnets
Prime examples of usefulness of magnetic force:
Electric power generators
Electric motors
Strong magnetic fields are used in:
MRI’s
microwave ovens
Earths magnetic field enabled:
The compass. (the needle always aligns itself with the magnetic field lines)
Magnetic field lines:
don’t originate in a single point.
The connection between electric and magnetic forces was first discovered by:
Oersted in 1819.
Found that moving a magnet near a conducting loop induces electric current and likewise, changing current inside a conducting loop will induce electric current in a nearby conducting electic loop.
Faraday
Magnetic field strength (B) is a: scalar or vector
vector
SI unit (measurement) of magnetic field strength (B):
(N/Am) Newton per ampere meter
(N/Am) =
(T) Tesla
The magnetic force points in the direction perpendicular to the plane that is defined by:
the velocity vector and the magnetic field vector.
The magnitude of the Lorentz force on a single particle where (q) is the charge of the particle, (v perpendicular) is the component of the particles velocity perpendicular to B, and (B) is the magnetic field strength.
F = q v perpendicular B
Lorentz force on a wire:
(I) current through the wire
(L) length of wire
(B) magnetic field
F = I L B
Paramagnetic materials that increase the magnetic field less than .1%
Uranium and platinum
- Diamagnetic materials
- decrease the magnetic field less than .1%
Bismuth, mercury, silver
will align their electron loops with each other, even when no external magnetic field is present
ferromagnetic
ex: iron cobalt and nickel
Amperes law for a long straight wire says the magnitude of the magnetic field strength produced by an infinitely long wire with current (I) inside is:
B = h I / r
(r) distance from the wire
(h) = 2x10^-7Tm/A
(I) current in wire.
AC electric motors create:
a rotating magnetic field
If a person winds a coil of wire around a steel rod, and then passes an electric current through the wire, then:
the steel rod becomes an electromagnet
magnetic fields are generated by:
electrons at rest, permanent magnets, moving charges
two wires with electric currents running parallel to each other experience:
a mutual attraction
two wires running antiparallel to each other experience:
a mutual repulsion
the force on a moving charge in the presence of a magnetic field is always
perpendicular to both the charges velocity and the magnetic field
the force on a moving charge in the presence of a magnetic field is always proportional to:
the velocity of the charge
the force on a moving charge parallel to a magnetic field is always
0
the force on a charge (q) moving with velocity (v) perpendicular to a magnetic field (B) is given by:
F = q v = B
two kinds of the same magnetic pole
repel each other
two kinds of the opposite magnetic pole
attract each other
