CHAPTER 8: Ohm’s law describes the Relationship of current, voltage, and resistance. UNIT 3: Electricity

ENERGY (E) – the ability to do work There are many forms of Energy kinetic, mechanical, chemical, solar... RECALL:

KINETIC ENERGY POTENTIAL ENERGY Energy of motion stored Energy ex: spring, elastic band Types of Energy

When + and – charges are pulled apart there are attractive forces wanting to put them back together, this is a form of potential energy as it has the ability to do work! Electric Potential Energy and Voltage Section 8.1 page 250

Stored electrical energy such as that stored in a battery Electric Potential Energy

Electrochemical Cell (Battery) Converts: Chemical Energy Electrical Energy + and – charges are separated into terminals located at either end of the cell, when connected – charges (electrons) travel towards the + (positive) terminal as the – charges repel one another

Batteries have electric potential Energy because the stored e-’s have the ability to do work, i.e. run your CD player!

An Electrochemical Cell Requires: different electrodes (usually metals also Carbon) And an electrolyte (electrolytic solution)

Change in potential energy per coulomb of charge Measured in volts (V) by a voltmeter Electric Potential Difference (Voltage)

Analogy! Stairs = the voltage Backpack = amount of charge separated More work has been done in B, therefore it has a greater Potential Energy!

Electric Circuit A complete pathway that allows electrons to flow Transforms electrical energy into other forms of Energy Interactive website Section 8.2 Electric Current page 260

Electric Circuit Analogy

Parts of an Electric Circuit Conductor – wire through which current flows Load – converts electrical E into other forms of E Switch – turn circuit on or off Source – source of electrical E Interactive Website on Switches

Circuit Diagram Symbols Interactive Website on Circuit Diagrams

Sample Circuit Diagram

THE CONTINUOUS FLOW OF CHARGE (ELECTRONS) IN A COMPLETE CIRCUIT Current Electricity

the amount of charge passing a given point in a conductor per second measured in amperes (A) by an ammeter or (mA) by a galvanometer Electric Current

Electrical Resistance: Slows down the flow of electrons and transforms electrical E into other forms of E Electrical E Light Heat Sound Motion etc Resistance & Ohm’s Law Section 8.3 page 270

Measured in ohms (Ω) Equal to the ratio of the voltage to the current R = V/I RESISTANCE

Current Dependent on Potential (voltage) Current Dependent on Resistance Resistance and Current Analogy:

Factors Affecting the Amount of Resistance in a wire include : 1. Length 2. Diameter (thickness) 3. Type of wire 4. Temperature

Resistance in a Light Bulb Long, Thin Tungsten wire Short, Thick copper wire

The Mathematical Relationship comparing voltage (V), current (I) and resistance (R) V = I ● R Interactive websiteInteractive website SimulationSimulation Ohm’s Law

Ohm’s Law – The VIR Tree V I R

Various Forms of Ohm’s Law V=I●R I = V R R = V I Where: V = voltage measured in volts (V) I = current measured in amperes (A) R = resistance measured in ohms (Ω)

STEP 1: Read and reread the question. Step up variables with known information. V = ? I= 0.5A R= 2Ω Use a question mark for the unknown value you are trying to find. Be sure to include units (V,A,Ω) Sample Problem: What voltage is used to run a flashlight with a 2 Ω resistor at a current of 0.5 A?

STEP 3: Convert units if necessary, measurements must be in V for voltage, A for current and Ω for resistance. Fill in the information given in the question (including units). STEP 2: Determine the form of ohm’s law needed to solve for the unknown in the question. V = I●R

V =I●R V = (0.5A)(2.0Ω) V= 1.0 V The flashlight would require a voltage of 1.0 V. STEP 4: Multiple or divide to calculate the unknown as per the formula chosen in step 3. Be sure to include units in your answer, round digits if necessary.

Used to control CURRENT or potential difference ( VOLTAGE ) in a circuit Resistor

RESISTANCE AND OHM’S LAW PAGE Core lab Activity: