» Current: rate at which electric charges move
though a given area (flow rate)
˃ Benjamin Franklin and Conventional Charge: the use of Franklins
original proposal that electricity is the flow of positive current through
a material, charge flows from positive to negative
˃ Electron flow: more recent system used for electricity that recognizes
that protons cannot leave the nucleus of an atom, but electrons can
hop from atom to atom.
˃ CHARGE (Q): measured in Coulombs
 Coulomb = 6.24 x 10 18 electrons
 Elementary Charge (q) = 1.6 x 10 -19 C
CALCULATIONS
Equation: 𝑰 =
𝑸
; Q=charge, I = current, t=time
∆𝒕
» Unit: Ampere (A) in Coulombs per second
Example: If the current in the wire of a Blu-ray player is 5.0 mA, how
long would it take for 2.0 C of charge to pass a point in the wire?
𝑰=
∆𝑸
∆𝒕
, ∆𝒕 =
∆𝑸
𝑰
; ∆𝒕 =
𝟐.𝟎 𝑪
=
.𝟎𝟎𝟎𝟓 𝑨
400 seconds
Active Components
» Batteries: convert chemical energy into
electrical potential energy
» Power Station/Generators: convert chemical
energy into mechanical energy and finally into
electrical energy
» Direct Current (DC) – charges move in only one
direction (batteries)
» Alternating Current (AC)- terminal of source is
constantly changing sign, causing charge to
move one way and then the other (generators,
home electric supply)
As current I flows through a given element in a circuit
it loses voltage V in the process
» This power dissipation is found using equations:
P=I×V
or
P = I 2× R
˃ Unit : Watts
∆𝑷𝑬
𝑽=
𝑸
↕rearrange
∆𝑷𝑬 = ∆𝑽𝑸
𝒂𝒏𝒅
W = ∆ E so:
𝑷=
∆𝑷𝑬
∆𝒕
=
𝑽𝑸
∆𝒕
𝑸
∆𝒕
= ∆𝑽𝑰
=I
∆𝑾
𝑷=
∆𝒕
Calculating the Electrical Energy Delivered in a
Time Interval
» Equation
E = IV Δt
E= electrical energy
I= current
V= voltage
t = time
Electricity and Heat: Calorimeter Lab
Specific Heat Capacity: amount of heat energy needed to raise
the temperature of 1g substance by 1°C
˃ Variable: C
˃ Unit: Joules per gram-degree Celsius (J / g °C)
˃ every substance will have a certain specific heat capacity,
Quantity of heat: amount of thermal energy transferred from
one object to another.
˃ Variable: Q (same as for charge, confusing I know)
˃ Unit: joules or calories (1 calorie is = to 4.18 Joules)
Equation:
Q= mC∆T or Q=mC (T2-T1)
m= mass
T= temperature
C= specific heat capacity of substance
Specific Heat Capacity of Common
Substances
Resistance: the opposition to the flow of current
in an electrical wire or element
˃ Think “friction”
˃ Symbol: R
˃ Unit : Ω (Omega) Ohm, equivalent to 1V/1A
˃ Equation: 𝑹 =
𝑽
𝑰
Equivalent Resistance: total resistance of a circuit based
on number of components and their configuration (series
or parallel)
» Series Rule: 𝑹𝑻𝒐𝒕𝒂𝒍 = 𝑹𝟏 + 𝑹𝟐 + 𝑹𝑵
» Parallel Rule:
𝟏
𝑹𝑻𝒐𝒕𝒂𝒍
=
𝟏
𝑹𝟏
+
𝟏
𝑹𝟐
+
𝟏
𝑹𝑵
NOTE: Rules only work when circuit, or portion of a circuit are only series or only
parallel
» Resistance is Dependent Upon:
˃ Length of wire/element: longer = ↑ resistance
˃ Cross-sectional area of wire/element: larger= ↓
resistance
˃ Material type: copper vs aluminum, etc.
˃ Temperature: decrease in temperature= ↓ resistance
» Named for Georg Simon Ohm (1789-1854)
𝑽 = 𝑰𝑹, where V is voltage, R is resistance and I is current
*only holds when Resistance is independent of Voltage
Not a fundamental Law, meaning it only holds
under certain conditions
» Ohmic: follows Ohm’s Law, using the equation the
resistance of a circuit can be calculated using
voltage and current
» Non- Ohmic: does not follow Ohm’s Law, equation
does not work due to variable resistance that is
dependent upon voltage
» Gustav Robert Kirchhoff, German Physicist (1824 –
1887)
» Credited with two laws essential to understanding
circuits.
1. Kirchhoff's Junction Rule
2. Kirchhoff’s Voltage Rule
Rule: At any node (junction or
branch point) in an electrical circuit,
the sum of currents flowing into that
node is equal to the sum of currents
flowing out of that node
» The algebraic sum of voltages around each
loop is zero
˃ Beginning with one node, add voltages
across each branch in the loop (if you
encounter a + sign first) and subtract
voltages (if you encounter a – sign first)
» Σ voltage drops - Σ voltage rises = 0
» Or Σ voltage drops = Σ voltage rises
Loop #3
6V
10 V
Loop #1
4V
4V
Loop #3
Loop #2
» Notes Circuit Resolution