59.60_Electromagnets-1
Оценка 4.8

# 59.60_Electromagnets-1

Оценка 4.8
pptx
08.05.2020
59.60_Electromagnets-1.pptx

Electromagnets

## Objectives Describe Hans Christian Ørsted’s discovery about current-carrying wires

Objectives

Describe Hans Christian Ørsted’s discovery about current-carrying wires.
Investigate and describe the relationship between electric current and magnetic fields in wires and solenoids.
Describe how electromagnets are used in many applications.

## Assessment 1. Which of the scientists listed below discovered that current-carrying wires create magnetic fields?

Assessment

1. Which of the scientists listed below discovered that current-carrying wires create magnetic fields?

Hans Christian Ørsted
James Clerk Maxwell
Alessandro Volta

## Assessment Describe one way that electromagnets are used in the present day

Assessment

Describe one way that electromagnets are used in the present day.

Name two ways to increase the strength of the magnetic field of a solenoid.

Physics terms

magnetic field
solenoid
electromagnet
polarity

## Before 1820, scientists suspected that electricity and magnetism were related, but they had no proof

Before 1820, scientists suspected that electricity and magnetism were related, but they had no proof.

Can you think of any similarities between electricity and magnetism that made scientists suspect a link?

## During a lecture in 1820, Danish physicist

Ørsted’s discovery

During a lecture in 1820, Danish physicist Hans Christian Ørsted finally discovered the connection.

A magnetic compass was lying near a wire. When he turned on the electric current in the wire, he saw the compass needle deflect.

A current-carrying wire creates a magnetic field!

I

## Currents create magnetism Current-carrying wires create magnetic fields

Currents create magnetism

Current-carrying wires create magnetic fields.

But what do these fields look like?

## Current-carrying wires create magnetic fields

Current-carrying wires create magnetic fields.

But what do these fields look like?

They circle around the wires!

Currents create magnetism

## The magnetic field circles around the current-carrying wire, and points tangent to the circle

The magnetic field circles around the current-carrying wire, and points tangent to the circle.

Currents create magnetism

## But which way does it circle?

But which way does it circle? Here are two possibilities:

direction of electric current

direction of magnetic field??

The magnetic field circles around the current-carrying wire, and points tangent to the circle.

Currents create magnetism

## Use the right-hand rule to find the direction of the magnetic field

Use the right-hand rule to find the direction of the magnetic field.

Direction of magnetic fields

Point the thumb of your right hand in the direction of the current.

Fingers curling around the wire point in the direction of the magnetic field.

## Think, pair, share: Strength of magnetic fields

Think, pair, share:

Strength of magnetic fields

What factors might affect the strength of the magnetic field around the wire?

direction of electric current

direction of magnetic field

## Strength of magnetic fields The field gets stronger as the current increases

Strength of magnetic fields

The field gets stronger as the current increases.

The field is stronger closer to the wire.

direction of electric current

direction of magnetic field

Think, pair, share:

What factors might affect the strength of the magnetic field around the wire?

## The solenoid The magnetic field around a single wire may not be very strong

The solenoid

The magnetic field around a single wire may not be very strong.

A solenoid uses many loops of current-carrying wire to create a stronger magnetic field.

## Electromagnets are made by wrapping a coil of wire around a iron core

Electromagnets are made by wrapping a coil of wire around a iron core.

The iron core makes the magnet even stronger.

Electromagnets

## Which end is north? To determine the magnetic

Which end is north?

To determine the magnetic North and South poles of an electromagnet, use another right hand rule:

Electromagnet polarity

Wrap fingers around the coil in the direction of the current.

Your thumb points in the direction of the North pole.

## In Investigation 19A you will build an electromagnet and test its strength and polarity (page 554)

In Investigation 19A you will build an electromagnet and test its strength and polarity (page 554).

Investigation

## Cut a 1-meter-long piece of wire

Cut a 1-meter-long piece of wire. Strip insulation from both ends.

Starting about 10 cm from one end of the wire, wrap the wire tightly around the nail.

Part 1: Build the electromagnet

Investigation

As you wrap the coil, make sure it is tight and that the wire does not cross itself.

## Stop wrapping about 1.0 cm before you get to the tip of the nail

Stop wrapping about 1.0 cm before you get to the tip of the nail. You should have at least 10 cm of free wire on this end.

Attach the wire at tip of the nail to the battery’s (+) terminal, and the other end of the wire to the (-) terminal.

Part 1: Build the electromagnet

Investigation

## Does your electromagnet deflect a compass needle?

Does your electromagnet deflect a compass needle?

How many paperclips can it lift?

Propose additional investigative questions: What variables could you change that might affect the strength of your electromagnet?

Investigation

Test the electromagnet

## Investigation Part 2: Determine its polarity

Investigation

Part 2: Determine its polarity

The polarity of a magnet indicates which end is north or south.

Using the right-hand rule, predict the polarity—which end is north and which is south—of your electromagnet. Justify your answer.

Using the compass, test your prediction. Were you right?

## Electromagnets have many useful applications, such as:

Electromagnets have many useful applications, such as:

Applications of electromagnets

The strength and polarity of electromagnets can be controlled by the adjusting the amount and direction of current and number of loops.

motors
computer hard drives

## This short video shows an electromagnet attached to a crane

This short video shows an electromagnet attached to a crane. It is being used to move scrap metal (page 553).

Applications of electromagnets

## What else? THINK: If electric currents can create magnetic fields, what

What else?

THINK:

If electric currents can create magnetic fields, what ELSE might be true?

Hint: it is something VERY useful!

## English physicist Michael Faraday demonstrated this opposite effect in 1822

English physicist Michael Faraday demonstrated this opposite effect in 1822.
This is how electric generators create the electricity that runs our homes and businesses.

Electric generators

Magnetic fields can create electric currents!

## By 1861 Scottish physicist James

By 1861 Scottish physicist James Clerk Maxwell had a complete theory of electromagnetism.

He summarized in his theory in four equations, now known as Maxwell’s equations.

Who else contributed?

## For further research on the historical development of the concept of the electromagnetic force:

For further research on the historical development of the concept of the electromagnetic force:

Verschuur, G. L. Hidden Attraction: The History and Mystery of Magnetism. (Oxford Univ. Press, 1976)

Meyer, H. W. A History of Electricity and Magnetism. (Burndy Library, 1971)

Hirshfeld, A. W. The Electric Life of Michael Faraday. (New York: Walker & Company, 2006)

For further research

## Assessment 1. Which of the scientists listed below discovered that current-carrying wires create magnetic fields?

Assessment

1. Which of the scientists listed below discovered that current-carrying wires create magnetic fields?

Hans Christian Ørsted
James Clerk Maxwell
Alessandro Volta

## Assessment 1. Which of the scientists listed below discovered that current-carrying wires create magnetic fields?

Assessment

1. Which of the scientists listed below discovered that current-carrying wires create magnetic fields?

Hans Christian Ørsted
James Clerk Maxwell
Alessandro Volta

## Assessment Describe one way that electromagnets are used in the present day

Assessment

Describe one way that electromagnets are used in the present day.

## Assessment Describe one way that electromagnets are used in the present day

Assessment

Describe one way that electromagnets are used in the present day.

Name two ways to increase the strength of the magnetic field of a solenoid.

Electromagnets are used in motors, computer hard drives, and on cranes to lift heavy metal objects, etc.

## Assessment Describe one way that electromagnets are used in the present day

Assessment

Describe one way that electromagnets are used in the present day.

Name two ways to increase the strength of the magnetic field of a solenoid.

Electromagnets are used in motors, computer hard drives, and on cranes to lift heavy metal objects, etc.

increase the current
increase the number of coils

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