Electricity and Magnetism
Chapter 16 Voltage, Energy, and Capacitance
Chapter 17 Current and Resistance
 16.1 Electrical Potential Energy
 16.2 Equipotentials and Electric Fields
 16.3-16.5 Capacitance and dielectrics
 17.1 Batteries and Direct Current
 17.2-.3: Current, Drift Velocity, Resistance
 17.4 Electrical Power
Chapter 19 Objectives
1. Describe the difference between current and voltage.
2. Describe the connection between voltage, current,
energy, and power.
3. Describe the function of a battery in a circuit.
4. Calculate the current in a circuit using Ohm’s law.
5. Draw and interpret a circuit diagram with wires,
battery, bulb, and switch.
6. Measure current, voltage, and resistance with a
multimeter.
7. Give examples and applications of conductors,
insulators, and semiconductors.
Chapter 19 Vocabulary Terms
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electricity
electric current
voltage
resistance
Ohm’s law
battery
open circuit
closed circuit
short circuit
 switch
 circuit diagram
 electrical
conductivity
 potentiometer
 wire
 volt
 electrical symbols
 amperes (amps)
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multimeter
ohm
resistor
ammeter
electrical
insulator
 semiconductor
 conductor
 electric circuit
19.2 Voltage
 Voltage, volts (V),is a measure of
electric potential energy per
charge)
 It is just like height is a measure
of gravitational potential energy.
 Work is the potential energy:
 W=qEr
 Q’s cancel.
V=Er
19.2 Voltage
 Voltage measures the
available electrical power
that flows.
 P=IV current*voltage
 1 joule per second is a
watt (power)
 1000 W happening for 1
hr is a kwh.
19.2 Voltage
 The positive end of a 1.5 volt
battery is 1.5 volts higher than
the negative end.
 Batteries positive-to-negative,
adds volts to the total.
 Each unit of current from the +
end of a three-battery stack
has 4.5 joules of energy.
19.2 What does a battery do?
 A battery uses chemical energy to move charges.
 If you connect a circuit with a battery the charges
flow out of the battery carrying energy.
19.1 Electric Circuits
Key Question:
What is an electric circuit?
19.1 Electric Circuits
 Electricity refers to the
presence of electric current
 Electric current is similar to
a current of water
 Electric current can carry a
lot of power.
19.1 Electric Circuits
 An electric circuit must have a complete path through
which electricity travels.
 Wires and electric circuits are similar to pipes carrying
water.
19.1 Electric Circuits
 A circuit diagram uses symbols to represent each part
 These electrical symbols are quicker and easy to draw
Current flows from + to -
19.2 Current and Voltage
Key Question:
How does current move
through a circuit?
19.2 Current and voltage
 Conventional current describes
the + as what is moving.
 Scientists later found that the
particles that carry electricity
actually travel from negative
 Today, we still use Franklin’s
definition.
19.2 Current and voltage
 Electric current is measured in
units called amperes, or amps
(A) for short.
 One amp is a flow of a certain
quantity of electricity in one
second.
 The amount of electric current
entering a circuit always equals
the amount exiting the circuit.
19.2 Current is a flow of charge
19.2 Current and voltage
 A battery uses chemical energy
to create a voltage (add
potential energy) between its
two terminals.
 Chemical reactions provide the
energy to pump the current
from low to high V.
 A fully charged battery adds
energy proportional to its
voltage.
19.2 How do these batteries differ?
 Some are smaller and don't store as much energy.
 Other batteries made with Ni and Cd can be recharged.
 Which battery above has the greatest voltage capacity?
19.2 Measuring Current
 In practical electricity,
we still label current
flowing from plus to
minus or HIGH voltage
to LOW voltage.
 Current can't be
measured unless the
charges flow through
the meter.
19.3 Electrical Resistance and Ohm’s
Law
Key Question:
How are voltage, current, and resistance related?
19.3 Electrical resistance
 Resistance measures how difficult it is for
current to flow.
19.3 Electrical Resistance
 The total amount of electrical resistance in a circuit
determines the amount of current that in the circuit for
a given voltage.
 The more resistance the circuit has, the less current
that flows.
19.3 Measuring resistance
 Set the meter to
measure resistance (W).
 Set the black and red
leads on opposite ends
of the objects.
19.3 The ohm
 Resistance is
measured in ohms
(W).
 One ohm is the
resistance when a
voltage of 1 volt is
applied with a
current of 1 amp.
19.3 Calculate current
 A light bulb with a resistance of 2 ohms is connected
in a circuit that has a single 1.5-volt battery.
 Calculate the current that flows in the circuit.
 Assume the wires have zero resistance.
Ohm’s Law
https://phet.colorado.edu/sims/ohmslaw/ohms-law_en.html
19.3 The resistance of electrical devices
19.3 The resistance of electrical devices
 Everything is designed with
a resistance made for the
voltage it was designed for.
19.3 Changing resistance
 The resistance of many
materials increases as
temperature increases.
 Resistors are devices
with constant resistance
V=IR so R=V/I
 would show a straight
line on this graph.
19.3 Electrical Conductivity
 The electrical conductivity describes a material’s
ability to pass electric current.
Resistance in a Wire
Conductors still have resistance.
https://phet.colorado.edu/sims/resistanc
e-in-a-wire/resistance-in-a-wire_en.html
19.3 Conductors and insulators
 Copper is a conductor
because it can conduct, or
carry, electric current.
 Materials that insulate (or
block) current flow are
electrical insulators.
 Semiconductors are neither
conductors nor insulators
19.3 Resistors
 Resisters resist current flow
 Resistors have striped color
codes to record their "values"
(writing on them is difficult).
19.3 Potentiometers
 Potentiometers are a type of "variable" resistor
 They are wired so that as you turn the knob, it
changes the distance the current has to flow.
Application: Hybrid Gas/Electric Cars
19.2 Measuring voltage of a cell
 Set the meter to DC volts.
 Touch the red (+) lead of
the meter to the (+) battery
terminal.
 Touch the black (-) lead of
the meter to the (-) battery
terminal.
 Adjust the meter dial as
necessary.
19.2 Measuring voltage in a circuit
 Measure the voltage
across the battery
exactly as before.
 DO NOT DISCONNECT
THE CIRCUIT.
NOTE: Since voltage is measured from
one point to another, we usually assign the
negative terminal of a battery to be zero
volts (0 V).