Transcript Electricity and Magnetism

Integrated Science
Unit 3, Chapter 7
Unit Three: Electricity and Magnetism
Chapter 7 Measuring Electricity
7.1
Voltage
7.2
Current
7.3
Resistance
Chapter 7 Learning Goals

Measure volts with an electrical meter.

Describe the role of a battery in a circuit.

Describe the transfer of energy in a circuit.

Explain the relationship between voltage and energy in a circuit.

Describe current as a flow of electric charge.

Measure amperes with an electrical meter.

Classify materials as conductors, semiconductors, or insulators.

Differentiate between electrical conductivity and resistance.

Explain why metals are good electrical conductors.

Measure ohms with an electrical meter.
Chapter 7 Vocabulary Terms

alternating current

ohm

ampere

resistance

battery

semiconductor

current

volt

direct current

voltage

electrical conductivity

electrical insulator

electrical conductor
7.1 Voltage
Key Question:
Why do charges move through a circuit?
7.1 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.
7.1 What does a battery do?

We measure the energy
level of any place in a
circuit in volts.

A fully charged battery
adds energy proportional
to its voltage.

The positive end of a 1.5
volt battery is 1.5 volts
higher in energy than the
negative end.
7.1 Voltage and Potential
 Voltage
is related to potential energy, just like
height is related to pressure in water flow.

A greater difference in height means that the
water has more potential energy.
 Differences
in electrical energy are measured
in volts.
 If
there is a difference in volts, current will flow
from the higher voltage to the lower voltage.
7.1 Voltage and Potential
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.
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).
7.1 Measuring Voltage
 Every
point in a circuit connected to the same
wire is at the same voltage
7.1 Voltage Drops
 If
we connect anything
that uses energy, like a
light bulb, we reduce
the voltage.
 Anything
that uses
energy (motors, bulbs,
resistors) lowers the
voltage since it takes
energy away.
7.1 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?
7.1 Mini Quiz
1.
Describe voltage?
2.
How are electrical differences measured ?
3.
What can you say about every point in a circuit
connected by the same wire?
4.
What is the voltage of the negative terminal of a
battery?
5.
What happens to the voltage when you connect
a battery to a circuit?
7.2 Current
Key Question:
How do charges move
through a circuit?
7.2 Current
 Current
is the flow of
electric charges.
 One
ampere is a flow
of one coulomb per
second.
7.2 Current is a flow of charge
7.2 Which way does
current flow?
 Either
positive or
negative charges can
flow.
 It
depends on the
materials making up the
circuit. We label circuits
from high to low current.
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.
7.2 Electricity in your house
These devices protect
you from short circuits
and fires.
7.2 AC or DC
 The
electricity in your house uses alternating
current, also called AC current. This means
the direction of the current goes back and
forth.
 The
current reverses direction 60 times per
second.
 The
A
hot wire carries 120 volts AC.
battery only makes current that flows in one
direction. This is called direct current, or DC.
7.2 Mini Quiz
1.
What is current?
2.
What are the units of current?
3.
What is the sign of the charges that move in a
wire?
4.
What supplies the energy to make the charges
flow?
5.
What type of current is used in homes? What
type is used in batteries?
7.3 Resistance
Key Question:
How well does current travel through
different materials and objects?
Measuring Resistance
 Set
the meter to
measure resistance (W).
 Set
the black and red
leads on opposite ends
of the objects.
7.3 Resistance

Resistance measures how difficult it is for
current to flow.
7.3 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.
7.3 Why does a bulb light?

A tungsten filament has a high
resistance and glows white
when it reaches 2,500 oC.

Argon gas inside the bulb is
"inert", it doesn't chemically
react with the tungsten so it
protects it from air for use over
and over again.
7.3 Mini Quiz
1.
What is a conductor?
2.
What is a semi-conductor?
3.
What is an insulator?
4.
What makes a material a conductor or an
insulator?
5.
What is resistance ?