Physics Class 4 Flashcards
Electric Charge
Unit: C
Symbol: Q or q
Can be positive or negative
Elementary Charge
The smallest possible unit of charge
1.6 x 10^-19 C
Coloumbs Law
Fe = K (|Q||q| /r^2) K = 9 x 10^9 Nxm^2 / C^2
If you know the electric field, you can find the electric force by:
Fe = qE
Because q is scalar, if it is a + direction, Fe is the same direction as E
If it is a - direction, fe is opposite direction as E
Electric Field from a point charge
Electric field moves away if +, towards if -
Unit: N/C
Equation: E = k x |Q|/r^2
Strength of electric field corresponds to ….
Density of the electric field
Electric potential vs electric field
Electric potential is the scalar field created by source charges that permeates space around them
Electric field is vector field created by source charges that permeates space around them
Electric potential
Changes in potential energy (similar to changes in height) are needed to calculate changes in electric PE
Unit: V (= J/C = PE/q)
Can be +, -, 0
Electric potential from a point charge
V = K x (q/r)
Electric Potential Energy
ΔPE = qΔφ = qV
Work done by electric field
W = -ΔPE
Positive charge wants to accelerate to regions of _____ electric potential
lower
Negative charge wants to accelerate to regions of _____ electric potential
higher
Batteries
Maintain potential difference
- Is NOT source of charge/enery
+ terminal = higher electric potential
- terminal = lower electric potential
Which direction does current flow from?
+ to -
Which direction do electron flow from?
- to +
Capacitors
Store energy & charge Formula: C= kEo(A/d) k = 1 if vaccum or air k>1 if another insulator Unit: Farads (F)
Q=CV
Charge on capacitor
- if capacitor is attached to battery in a closed circut
Energy stores by capacitor
PEcap = 1/2QV
= 1/2CV^2
= Q^2 /2C
Calculating electric field with capacitor
E = V/d
- electric field goes from + to -
Dielectrics
Opposite direction of electric field
- makes it more difficult for charges to attract, thus increasing resistance so you can store more charge by increasing capacitance
Conductor
Charges move freely
Applying a potential difference (voltage) across a conductor induces a net movement of charge
Dielectric breakdown
Insulator is ionized by too large of an external electric field, allowing charges to move through it
Ohm’s Law
V=IR
Flow rate of charge
Formula = I = ΔQ/Δt
Units: Amps = c/s
What does the slop of a V(voltage) x I (current) graph give you?
J/s = Watts = Power
Resistance
How much an OBJECT opposes the charge through it
R = ρ(L/A)
Units: Ω
Resistivity (ρ)
How much a MATERIAL opposes the flow of charge through it
Units: ρ = Ω x m
One battery + One resistor
Voltage of the battery determines voltage across resistor
Voltage of battery = Voltage of resistor
Resistors in series vs parallel
Series = same CURRENT Req = R1 + R2+ R3 ... Req = V1/i + V2/i + V3/i+...
Parallel = same Voltage 1/Req = 1/R1 + 1/R2 + 1/R3 ... Req = I1/V + I2/V + I3/V+...
