Transcript Chapter 8 Slide Show

UNIT 3: Electricity
CHAPTER 8: Ohm’s law
describes the Relationship of
current, voltage, and
resistance .
RECALL:
ENERGY (E) – the ability to do work
 There are many
forms of Energy
kinetic,
mechanical,
chemical,
solar...
Types of Energy
KINETIC ENERGY
 Energy of motion
POTENTIAL ENERGY
 stored Energy
ex: spring, elastic band
Electric Potential Energy and Voltage
Section 8.1
 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!
page 250
Electric Potential Energy
Stored electrical energy such
as that stored in a battery
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)
Electric Potential
Difference (Voltage)
Change in potential
energy per coulomb of
charge
Measured in
by a
volts (V)
voltmeter
Analogy!
 Stairs = the voltage
 Backpack = amount
of charge separated
 More work has
been done in B,
therefore it has a
greater Potential
Energy!
Section 8.2
Electric Current
page 260
Electric Circuit
 A complete pathway
that allows electrons
to flow
 Transforms
electrical energy
into other forms of
Energy
 Interactive website
Electric
Circuit
Analogy
Parts of an Electric Circuit
Source – source of
electrical E
Switch – turn
circuit on or off
Interactive Website on Switches
Conductor – wire
through which
current flows
Load – converts
electrical E into
other forms of E
Circuit Diagram Symbols
Interactive Website on Circuit Diagrams
Sample
Circuit
Diagram
Current Electricity
THE CONTINUOUS FLOW OF
CHARGE (ELECTRONS) IN A
COMPLETE CIRCUIT
Electric Current
•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
Resistance & Ohm’s Law
Section 8.3
page 270
Electrical Resistance:
 Slows down the flow
of electrons and
transforms electrical E
into other forms of E
 Light
 Heat
 Sound
Electrical E
 Motion
 etc
RESISTANCE
•Measured in ohms ( Ω)
•Equal to the ratio of the voltage to
the current
R = V/I
Resistance and Current Analogy:
Current Dependent
on Potential (voltage)
Current Dependent
on Resistance
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
Ohm’s Law
The Mathematical Relationship
comparing
voltage (V), current (I) and resistance (R)
V = I●R
Interactive website
Simulation
Ohm’s Law – The
VIR Tree
V
I
R
Various Forms of Ohm’s Law
Where:
V=I●R
I=V
R
R=V
I
 V = voltage measured in
volts (V)
 I = current measured in
amperes (A)
 R = resistance measured
in ohms (Ω)
Sample Problem: What voltage is used
to run a flashlight with a 2 Ω resistor
at a current of 0.5 A?
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)
STEP 2: Determine the form of ohm’s law
needed to solve for the unknown in the
question.
V = I●R
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 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.
V =I●R
V = (0.5A)(2.0 Ω)
V= 1.0 V
The flashlight would require a
voltage of 1.0 V.
Resistor
Used to
control
C U R R E N T or
potential
difference
( V O L T A G E ) in a
circuit
Core lab Activity:
RESISTANCE AND OHM’S LAW
PAGE 278-9