Circuits, Electricity and Magnetism

Introduction

Electricity and Magnetism

Electricity and magnetism are
closely connected because
charged particles create both.
Electricity is moving electrons,
and moving electrons create a
magnetic field. We don't know
exactly why moving charges
create magnetic fields, but they
do.

As humans, we have learned
how to harness moving
electrons' energy to make our
lives easier with electricity and
magnetism.

Multiple Choice

Atoms have protons, neutrons, and ....

• photons

• electrons

• energy

Multiple Choice

Positive and Positive charges ________

• Attract

• Repel

Multiple Choice

Negative and Positive charges ________

• Attract

• Negative

Multiple Choice

The force between charged particles is called ________

• Kinetic Force

• Thermal Force

• Electric Force

The Electric Field

Electricity and Magnetism

The electrical force pulls opposite charges together and pushes apart like charges.

The electrical force created by a charged particle forms an electric field around the particle.

Scientists draw field lines to model the electrical force.

All of the protons and electrons in an atom have an electric field around them.

Electrons are attracted to protons, but other electrons repel them. Changes in the electric fields around them cause electrons to jump on and off of atoms.

Remember, electrons can move, but protons can't because they are trapped in the atom's nucleus.

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Static Electricity

Electricity and Magnetism

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The negative charges on one side of the balloon repel the electrons in the wall and are attracted to the positive charges in the wall.

Sometimes static electricity will give you a shock.
When your hand has extra electrons, they are
repelling each other because of the electrical force.

If you bring your hand close to a conductor, such as a metal doorknob, the electrons will jump from your
hand to the atoms on the doorknob. When electrons
jump onto an atom, they release light and heat, so
you feel a shock.

Lightning is created by static electricity building up in clouds. When the extra electrons jump to new atoms, they make lightning.

Static electricity happens when charges build up in one place. Static electricity is what causes a balloon to stick to a wall.

Multiple Choice

Static Electricity is .....

• the release of electrons

• a build up of electrons

Induction

Electricity and Magnetism

When two objects rub together, their atoms get
incredibly close, and electrons can jump from an atom
on one object to an atom on the other object.


For example, when you rub a balloon with a wool cloth, the balloon collects electrons and becomes negatively
charged.

Changing the charge on an object using a charged object is called induction.

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Multiple Choice

Changing the charge of an object using another charged object is called ....

• Energy

• Electricity

• Induction

Insulators and Conductors

Electricity and Magnetism

How electrons move through a material determines if it will be an insulator or a conductor. Insulators are made up of atoms in covalent bonds that hold their electrons tightly and don’t let them move through the material.


Plastics, paper, rubber, glass, wood, and dry air are all examples of insulators. Pure water is another insulator, but all of the water found naturally on Earth has impurities, such as salt, that make it a
conductor.

Unlike insulators, conductors let electrons move freely through them. Conductors have more metallic and ionic bonds where the electrons aren’t stuck to one atom, but they move from atom to atom within the material. Metals, graphite, water with impurities, and the human body are all conductors.

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Multiple Choice

An insulator .....

• slows/stops electrons

• speeds electrons

Multiple Choice

A conductor ....

• slows/stops electrons

• speeds electrons

Labelling

Conductor or Insulator

Drag labels to their correct position on the image

Conductor

Insulator

Labelling

Conductor or Insulator

Drag labels to their correct position on the image

Conductor

Insulator

Labelling

Conductor or Insulator

Drag labels to their correct position on the image

Insulator

Conductor

Labelling

Conductor or Insulator

Drag labels to their correct position on the image

Conductor

Insulator

Electrical Circuits

Electricity and Magnetism

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An electrical circuit usually has a load, an object that is converting the electrons'
electrical energy into another form of energy, such as light energy.

The circuit can also have a switch. When the switch is on, electrons flow through it to complete the circuit. When the switch is off, electrons can't complete the circuit and stop moving.

There are three types of circuits. A simple circuit has one power source and one load. The next circuits are Series and parallel circuits that have either multiple power sources or multiple loads.

An electrical circuit provides a path for electrons to follow. An electrical circuit must have a conductor, usually a wire, for the electrons to travel through, and a power source, such as a battery.

Multiple Select

A circuit has...

• load

• power source

• a flux capacitor

• conductor

In a series circuit, everything is lined up so that electrons have to pass through everything along the circuit.

In a series circuit, the voltage is split between the loads, but the current remains the same.

​In a parallel circuit, power sources or loads are put on different paths, so electrons do not pass through all of them.

In a parallel circuit, the current is split between the loads, but the voltage is the same.

Multiple Choice

What kind of circuit is this?

• Simple

• Series

• Parallel

Multiple Choice

What kind of circuit is this?

• Simple

• Series

• Parallel

Multiple Choice

What kind of circuit is this?

• Simple

• Series

• Parallel

Multiple Choice

What kind of circuit is this?

• Simple

• Series

• Parallel

Multiple Choice

What kind of circuit is this?

• Simple

• Series

• Parallel

Resistance

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When electrons get close to each other, they slow down.
Electrons are more likely to run into each other in a thin wire than a thick wire. This is similar to you trying to get to class. You will be more likely to bump into other students in narrow hallways than wide hallways.

Humans use resistors to convert electrical energy into
other forms of energy. For example, the lightbulb has a thin piece of wire. As electrons move through it, they slow down and release energy.

The energy released is transformed into light and thermal
energy. Toasters transform electrical energy into thermal
energy, and moving toys can transform electrical energy
into mechanical energy.

Resistance measures how difficult it is for electrons to flow through a material. It is measured in ohms.

Conductors have low resistance, and insulators have high resistance. We can also change resistance by changing the thickness of a wire.

Ohm’s Law

George Ohm was a German physicist who lived from
1789 to 1854. Working with electrical current, Ohm
realized that the speed of the current, voltage, and
resistance were all related. He put his theory into an
equation that we now call Ohm’s Law.

Current = Voltage/resistance

C=V/R

Remember, current is the stream of electrons in a circuit

and voltage is the difference in potential electric energy between two points (pressure that pushes electricity).

At first, Ohm’s law was not well received by the scientific
community. Ohm was so frustrated he quit his teaching
job. Later, scientists came to appreciate Ohm’s law, and
the unit for resistance, the ohm, was named after him.

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Current (i)= V/R

​Voltage= 30 V
Resistance= 5 A
i = ?

​Example:

Current (i)= V/R

​Voltage= 30 V
Resistance= 5 A
i = ?

​Example:

​i = 30/5
i =

Current (i)= V/R

​Voltage= 30 V
Resistance= 5 A
i = ?

​Example:

​i = 30/5
i =

​Example:

​Resistance= 6 A
Current= 20 V
Voltage = ?

Current (i)= V/R

​Voltage= 30 V
Resistance= 5 A
i = ?

​Example:

​i = 30/5
i =

​Example:

​Resistance= 6 A
Current= 20 V
Voltage = ?

​20 = V/6
x6 x6
20 x 6 = V
= V

Review

Electricity and Magnetism

Multiply or divide to solve for the missing quantity using Ohm’s Law.

voltage: 56 V
current: 8 A

resistance: ___Ω

voltage: ___ V
current: 4 A

resistance: 7Ω

voltage: 27 V
current: 9 A

resistance: ___Ω

voltage: 81 V
current: ___ A
resistance: 9Ω

voltage: ___ V
current: 3 A

resistance: 6Ω

voltage: 45 V
current: ___ A
resistance: 5Ω

Fill in the Blank

Voltage: 56 V

Current: 8 A

Resistance: ?

Fill in the Blank

Voltage: ? V

Current: 4 A

Resistance: 7

Fill in the Blank

Voltage: 27 V

Current: 9 A

Resistance: ?

Fill in the Blank

Voltage: 81 V

Current: ? A

Resistance: 9

Fill in the Blank

Voltage: ? V

Current: 4 A

Resistance: 6

Conservation of Energy

Electricity and Magnetism

The law of conservation of energy says that energy cannot be created or destroyed, but it can be transformed into different types of energy. For example, a light bulb can convert electrical energy into light energy.

Sometimes it appears as if energy
disappears. This happens when energy is
transformed into thermal energy. Thermal
energy releases into the environment, so it is difficult to see.

Light bulbs convert electrical energy into light energy, but, in incandescent light bulbs, about 90% of the electrical energy is lost to thermal energy instead of light energy.

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LIGHT ENERGY
THERMAL ENERGY

ELECTRICAL ENERGY

Multiple Choice

Energy can be created and destroyed

• True

• False

Magnetic Fields

Electricity and Magnetism

Every magnet has a north pole and a south pole.
Magnetic force pushes away from the north pole and
pulls into the south pole.

A magnetic field is the area around the magnet affected
by the magnetic force. Scientists draw field lines to show
a magnetic field. The closer together the field lines are
drawn, the stronger the magnetic force.

Swirling iron in the Earth’s outer core creates a giant
magnetic field around the Earth. Our planet’s magnetic field deflects dangerous charged particles in the solar wind from the Sun.

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Electromagnetism

Electricity and Magnetism

Hans Christian Oersted, a Danish physicist, accidentally
discovered electromagnetism in 1820 when he held a
compass near a wire carrying an electrical current. The
compass needle moved when Oersted placed next to
the wire, so he realized electricity and magnetism must
be connected.

Scientists have found that a coiled wire carrying
electrical charges creates a stronger magnetic field
than a straight wire, and more coils in the wire create a stronger magnetic field.

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Moving electrical charges create a magnetic field. The reason this happens has to do with the laws of relativity.

Stationary electrical charges do not create a magnetic field, but a magnetic force pushes outwards around them when electrons move. The Sun’s magnetic field is created by moving electrons.

Multiple Choice

What is induction?

• Build up of electrons

• changing the charge of an object

• speeding up electrons

Multiple Choice

What is the difference between an insulator and a conductor?

• Insulators slow electrons

  Conductors speed electrons

• Insulators speed electrons

  Conductors slow electrons

• No difference really

Multiple Choice

What two things create magnetic fields?

• Electricity and power

• North Poles

  and

  South Poles

• Will power

  and

  determination