1. Current, Power Dissipation, Ohm’s Law and Equivalent Resistance

2. Current and Charge
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 = x electrons
Elementary Charge (q) = 1.6 x C

3. 𝑰= ∆𝑸 ∆𝒕 ,∆𝒕= ∆𝑸 𝑰 ; ∆𝒕= 𝟐.𝟎 𝑪 .𝟎𝟎𝟎𝟓 𝑨 = 400 seconds
Current and Charge
CALCULATIONS
Equation: 𝑰= 𝑸 ∆𝒕 ; Q=charge, I = current, t=time
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

4. Sources of Current Active Components
Batteries: convert chemical energy into electrical potential energy
Power Station/Generators: convert chemical energy into mechanical energy and finally into electrical energy

5. 2 Types of Current
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)

6. Power Dissipation P = I × V or P = I 2× R
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

7. Deriving Power Equation
𝑽= ∆𝑷𝑬 𝑸 𝒂𝒏𝒅 𝑷= ∆𝑾 ∆𝒕 ↕rearrange ∆𝑷𝑬=∆𝑽𝑸 W = ∆ E so: 𝑷= ∆𝑷𝑬 ∆𝒕 = 𝑽 𝑸 ∆𝒕 = ∆𝑽𝑰
𝑸 ∆𝒕 = I

8. Calculating the Electrical Energy Delivered in a Time Interval
Equation
E = IV Δt
E= electrical energy
I= current
V= voltage
t = time

9. Electricity and Heat: Calorimeter Lab

10. Thermodynamics and Electricity
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

11. Specific Heat Capacity of Common Substances

12. Resistance
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

13. Rules for Resistance in Circuits
Equivalent Resistance: total resistance of a circuit based on number of components and their configuration (series or parallel)
Series Rule: 𝑹 𝑻𝒐𝒕𝒂𝒍 = 𝑹 𝟏 + 𝑹 𝟐 + 𝑹 𝑵
Parallel Rule: 𝟏 𝑹 𝑻𝒐𝒕𝒂𝒍 = 𝟏 𝑹 𝟏 + 𝟏 𝑹 𝟐 + 𝟏 𝑹 𝑵
NOTE: Rules only work when circuit, or portion of a circuit are only series or only parallel

14. Resistance 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

15. Ohm’s Law 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

16. Ohmic vs Non-Ohmic Devices
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

17. Kirchhoffs 2 Laws
Gustav Robert Kirchhoff, German Physicist (1824 – 1887)
Credited with two laws essential to understanding circuits.
Kirchhoff's Junction Rule
Kirchhoff’s Voltage Rule

18. Kirchhoff’s Junction 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

19. Kirchoff’s Voltage Law (KVL)
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

20. KVL Example
Loop #3
6 V 4V
10 V
Loop #1 4V
Loop #2
Loop #3

21. Notes Circuit Resolution