chapter 8: ohm’s law describes the relationship of current, voltage, and resistance. unit 3:...
TRANSCRIPT
CHAPTER 8: Ohm’s law describes the Relationship of
current, voltage, and resistance.
UNIT 3: Electricity
ENERGY (E) – the ability to do workENERGY (E) – the ability to do work
There are many forms of Energy
kinetic, mechanical,
chemical, solar...
RECALL:
KINETIC ENERGYKINETIC ENERGY POTENTIAL ENERGYPOTENTIAL ENERGY
Energy of motion stored Energyex: 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 CircuitElectric 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
SampleCircuit Diagra
m
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: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 Potential (voltage)
Current Dependent on ResistanceCurrent 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 BulbLong, Thin Tungsten
wire
Short, Thick copper wire
The Mathematical Relationship comparing
voltage (V), current (I) and resistance (R)
V = IR
Interactive website Simulation
Ohm’s Law
Ohm’s Law – The VIR Tree
V
I R
Various Forms of Ohm’s Law
V=IR
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= 0.5AR= 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 = IR
V =IRV = (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 LAWPAGE 278-9
Core lab Activity: