Transcript Resistance and Ohm`s Law

BrainPop Movie:
Current Electricity
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Electric Circuits
Current and Voltage
Resistance and Ohm's Law
*
*Electric current is
similar in some ways to
a current of water.
*Like electric current,
water current can carry
energy and do work.
*A waterwheel turns
when a current of
water exerts a force on
it.
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*An electric circuit is a complete
path through which electric current
travels.
*A good example of a circuit is the
one found in an electric toaster.
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*Wires in electric circuits are similar in
some ways to pipes and hoses that carry
water.
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These are some examples of
natural electrical circuits:
1. The nerves in your body form an electrical
circuit that carries messages from your brain
to your muscles and other parts of the body.
2. The tail of an electric eel makes a circuit
when it stuns its prey with a jolt of
electricity.
3. An electric circuit with a large amount of
energy is formed when lightning carries
electric current between clouds and the
ground.
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*When drawing a circuit diagram,
symbols are used to represent each
part of the circuit.
*
*Electrical
symbols are
quicker and
easier to draw
than realistic
pictures of the
components.
*
*Electric current is caused by moving
electric charge.
*Electric current comes from the
motion of electrons.
*
*A resistor is an electrical device that
uses the energy carried by electric
current in a specific way.
*Any electrical device that uses
energy can be shown with a resistor
symbol.
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*Current only flows
when there is a
complete and
unbroken path, or
a closed circuit.
*Flipping a switch
to the “off”
position creates an
open circuit by
making a break in
the wire.
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Electric Circuits
Current and Voltage
Resistance and Ohm's Law
*
*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.
*
*Voltage is a measure of
electric potential energy, just
like height is a measure of
gravitational potential energy.
*Voltage is measured in volts
(V).
*A voltage difference of 1 volt
means 1 amp of current does
1 joule of work in 1 second.
*
*A difference in voltage provides the
energy that causes current to flow.
*
*A useful meter is a
multimeter, which
can measure voltage
or current, and
sometimes resistance.
*To measure voltage,
the meter’s probes are
touched to two places
in a circuit or across a
battery.
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*A battery uses stored
chemical energy to
create the voltage
difference.
*Three 1.5-volt batteries
can be stacked to make
a total voltage of 4.5
volts in a flashlight.
*
*A pump is like a battery because it
brings water from a position of low
energy to high energy.
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*Circuit breakers and fuses are two
kinds of devices that protect circuits
from too much current by making a
break that stops the current.
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Electric Circuits
Current and Voltage
Resistance and Ohm's Law
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*Resistance is the
measure of how
strongly an object
resists current flowing
through it.
*The relationship
between electric
current and resistance
can be compared with
water flowing from the
open end of a bottle.
*
*The total amount of resistance in a
circuit determines the amount of
current in the circuit for a given
voltage.
*
* Electrical resistance is measured in
units called ohms.
* This unit is abbreviated with the
Greek letter omega (Ω).
*
*The current in a circuit depends on
voltage and resistance.
*Ohm’s law relates current, voltage, and
resistance with one formula.
*If you know two of the three quantities,
you can use Ohm’s law to find the third.
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A toaster has a resistance of 12
ohms and is plugged into a 120volt outlet. How much current
in amps does it use?
1. Looking for: the current in amps
2. Given: resistance (12 Ω ) and voltage
(120 V)
3. Relationships: Use: I = V ÷ R
4. Solution: I = 120 V ÷ 12  = 10 A
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*Every electrical
device is designed
with a resistor
that causes the
right amount of
current to flow
when the device is
connected to
voltage.
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*The resistance of many
electrical devices varies
with temperature and
current.
*A light bulb’s resistance
increases when there is
more current because
the bulb gets hotter
when more current
passes through it.
*You are Wired!
*Your nervous system uses specialized cells
called neurons to transfer electrical signals
from one part of your body to another.
*A neuron has three basic parts: the cell
body; a long, thin portion called the axon;
and fingerlike projections called dendrites.
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* 2 page version:
Key Question: How do you measure voltage and current in electric circuits?
GUIDED NOTES FOR “ELECTRICITY AND ELECTRIC CIRCUITS”
 __________________________ __________________________ is similar in some ways to a current of water.
Electric current
 ______________ ______________ is similar in some ways to a current of water.
 Like electric current, water current can carry __________________________ and do __________________________ .
 Like electric current, water current can carry ______________ and do ______________ .
 A waterwheel turns when a current of water exerts a __________________________ on it.
 A waterwheel turns when a current of water exerts a ______________ on it.
 An __________________________ __________________________ is a complete path through which electric current travels.
 Wires in electric circuits are similar in some ways to __________________________ and __________________________ that carry water.
Electric Circuits
Natural circuits
 An ______________ ______________ is a complete path through which electric current travels.
 These are some examples of natural electrical circuits:
 A good example of a circuit is the one found in an electric ______________ .
1. The __________________________ in your body form an electrical circuit that carries messages from your
__________________________ to your __________________________ and other parts of the body.
Electric Circuits
2. The tail of an electric __________________________ makes a circuit when it stuns its prey with a jolt of electricity.
 Wires in electric circuits are similar in some ways to ______________ and ______________ that carry water.
3. An electric circuit with a large amount of energy is formed when __________________________ carries electric current between
Natural circuits
__________________________ and the __________________________ .
 These are some examples of natural electrical circuits:
Electric Circuits
 When drawing a __________________________ __________________________ , symbols are used to represent each part of the circuit.
1. The ______________ in your body form an electrical circuit that carries messages from your
______________ to your ______________ and other parts of the body.
 __________________________ __________________________ are quicker and easier to draw than realistic pictures of the components.
2. The tail of an electric ______________ makes a circuit when it stuns its prey with a jolt of electricity.
3. An electric circuit with a large amount of energy is formed when ______________ carries electric
current between ______________ and the ______________ .
 __________________________ __________________________ is caused by moving electric charge.
 Electric current comes from the motion of ____________________________________________________ .
Resistors
Electric Circuits
 When drawing a ______________ ______________ , symbols are used to represent each part of the circuit.

A __________________________ is an electrical device that uses the energy carried by electric current in a specific way.

__________________________ electrical device that uses energy can be shown with a resistor symbol.
Current in a circuit
Electric Circuits
 ______________ ______________ are quicker and easier to draw than realistic pictures of the components.
Electric current


Current only flows when there is a complete and unbroken path, or a __________________________ __________________________ .
Flipping a _________________________ to the “off” position creates an ______________________ ________________________ by
making a break in the wire.
Resistance and Ohm's Law
Current and voltage
 ______________ ______________ is caused by moving electric charge.
 _______________________ _______________________ is measured in units called _________________________ , or amps (A) for short.
 Electric current comes from the motion of ____________________________ .
 One amp is a flow of a certain quantity of electricity in one __________________________ .
Resistors
 A ______________ is an electrical device that uses the energy carried by electric current in a specific way.
 ______________ electrical device that uses energy can be shown with a resistor symbol.
Current in a circuit
 Current only flows when there is a complete and unbroken path, or a ______________ ______________ .
 Flipping a ______________ to the “off” position creates an ______________ ______________ by making a
break in the wire.
 The amount of electric current entering a circuit __________________________ equals the amount exiting the circuit.
Voltage
 Voltage is a measure of electric __________________________ __________________________ , just like height is a measure of
gravitational potential energy.
 Voltage is measured in __________________________ (V).
 A voltage difference of 1 volt means 1 amp of current does 1 joule of work in 1 second.
 A __________________________ in voltage provides the energy that causes current to flow.
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Key Question:
How do you measure voltage and
current in electric circuits?
Objectives:
Build simple circuits and draw circuit diagrams.
 Measure current and voltage in a battery.
 Identify electrical conductors and insulators.
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Key Questions:
What is the relationship between
current, voltage and resistance?
Objectives:
Measure resistance in a circuit.
 Use Ohm’s law to identify the mystery resistor in a circuit.
 Investigate the relationship between voltage drop across
the potentiometer and voltage drop across the bulb in a
circuit.
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Key Questions:
How can you use electricity to test
your manual dexterity?
Objectives:

Apply their knowledge of electric circuits to build a game.
Analyze the construction of the game in terms of electrical
conductivity.
 Consider the effects of varying the construction of the electric
circuits game.
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