University:
The University Of Western Ontario
Course:
2223B | Organic Chemistry of Biological Molecules
Academic year:

2023
Views:

271

Pages:

1
Author:

Cole M.

Current & Resistance Current & Resistance: Electrons actually move pretty slowly through direct current circuits Electrons don't really move in alternating current circuits - Introduction to Circuits & Ohm’s Law: Ohm’s Law connects the ideas of voltage (V), current (I), and resistance (R) → V = IR Current is simply the amount of charge per unit time (Q/tr C/s) and is measured in units of amps Conventional current is the flow of positive charge (positive terminal to negative terminal) Resistance is how much charge flow is impeded in its path and is measured in units of ohms Resistors in Series: The higher the voltage, the more that the electrons want to get to the positive terminal of the battery Assume all wires (without any resistors present) have no resistance Current is the same throughout a loop in series When in series, RT = R1 + R2 + R3 Resistors in Parallel: In parallel, IT = I1 + I2 For resistors, (RT)-1 = (R1 + R2)-1 Once you find total resistance in parallel, you can just combine them as one and make the resistance equal to the total resistance across that area that is in parallel - Resistivity & Conductivity: Resistance is a constant if it is an ohmic resistor (since if you increase voltage, current increases proportionally) Increasing distance (L) of the resistor will increase resistance Increasing the cross sectional area (A) of the resistor will decrease resistance The material that the resistor is made of can also change the resistance of the resistor (symbol for resistivity is 𝜌 in units of ohms*m) Therefore, R = 𝜌L/A Remember resistivity is difference from resistance Conductivity refers to how much something allows current to flow (shown by the symbol σ) Resistivity and conductivity are related by 𝜌 = 1/σ Therefore if something is a good conductor, its a bad resistor, and if it's a good resistor, then its a bad conductor Electrolytic Conductivity: You want to use plates in order to find the conductivity because they have a defined cross sectional area Voltmeters & Ammeters: Place the voltmeter ends on either side of a resistor in order to find the resistance drop across that resistor (in parallel) → have very high resistances For an ammeter you do NOT hook it up in parallel, you need to hook it up in series (must disconnected/break circuit in order to measure the current) → have very little resistance Extra Notes: For power, P = VI = V2/R = I2R