Electricity And Magnetism Flashcards
Voltage
Creates current
= change in electrical potential
= current * resistance
Current
= net movement of charge
Charge/time
Direct current= current flowing in one direction
Steady voltage and current over time
Alternating current= current changes direction
Creates a sinusoidally varying voltage and current over time
Rms Voltage= voltage/(sqroot 2)
Rms current = current/(sqroot 2)
Resistance
=Voltage/current
Intrinsic resistance is resistivity which is denoted by p
Resistance= resistivity *(length/area)
Resistors
=a component in an electric current that has a specific resistance
Series
Current is the same throughout the circuit
Resistance is R1+R2+…
Voltage of circuit is V1+V2
Capacitance is (1/C1)+(1/C2)+…
Parallel circuit
Voltage is the same throughout the circuit
Resistance is (1/R1) + (1/R2)
Current is I1 +I2
Capacitance=C1+C2+…
Power dissipated by resistor
=(current^2) * resistance
Or
= current*voltage( of that resistor)
Power of entire circuit
= current* voltage
Energy
= power * time
Internal resistance
Denoted by r
Causes the voltage between the positive and negative terminal to be different from the emf or ideal voltage
Terminal voltage V= emf- Ir
However if circuit is supplying current to the battery ( charging it) then V= emf + Ir
Ideal batteries have no internal resistance
Capacitor
A pair of conductors that hold equal but opposite charges so that net charge is zero
To create a charged capacitor- hook plates to the terminals of a battery( charge will stop when potential difference between plates matches the voltage of battery-plate connected to positive terminal becomes more positive and has a higher potential)
Q= CV
Charge on capacitor= capacitance * voltage
Capacitance depends on size of plates and how far apart they are
Purpose: to create a uniform electric field and store electrical potential energy
Voltage of capacitor=electric field * separation distance
Capacitance
= permittivity of free space* (area of each plate/separation)
Permittivity of free space=1/(4pi Coulomb constant)
Coulomb constant = 9 x 10^-12
Electrical potential energy stored in capacitor
=0.5chargevoltage
Discharging a capacitor
Recapturing stored electrical energy
Rate at which charge leaves isn’t linearly it’s rapid then a slow decrease
Dielectrics
An insulator loaded between the plates of a capacitor and prevent them from touching
Presence always increases capacitance
C( with dielectric)= K(dielectric constant) * C(without dielectric)
K=1 in a vacuum or air
Effects of the insertion of a dielectric
After battery disconnected- C increases by a factor of K, Q stays constant, Voltage and potential energy decreases by a factor of K( energy lost as heat)
With battery connected- PE, C and Q increases by a factor of K, voltage and electric field stay the same
Dielectric breakdowns
Extra electrons on the negative plate jump across the gap to the positive plate instead of traveling down the conduction worse when the electric field strength exceeded the maximum value then the dielectric becomes ionized and acts as a conduction pathway
Magnetic fields
Created by moving electric charges or currents
Magnetic force(Fb) = q( v x B) Cross product of velocity of charge bad magnetic field
B for long straight wire is inversely proportional to distance from wire
Fb= qvBsin(theta)
Direction of force is always perpendicular to velocity and magnetic field
Dots mean out of page
X means into page
Time to complete one revolution
= (2piradius) /velocity
Solenoid
Helical coil of wires in which the magnetic field on the inside is parallel to central axis and is strongest on the central axis and gets weaker as we move away from center
Magnetic fiels is proportional to current *(number of turns/ length)
Magnets
Magnetic field emanates from north to South Pole
Can’t have a pole by itself