Electricity and Magnetism

 

Resources: ThinkQuest.org; University of Chile (Hong Kong Polytechnic University); University of Colorado at Boulder, Electrical Safety.com; The Physics Classroom

 

 

10.1 Electricity and Magnetism

a. Describe and provide examples of electrostatic and magnetostatic phenomena
b. Predict charges or poles based on attraction/repulsion observations
c. Build a simple compass See instructions below blue print.-Use the compass to determine the direction of magnetic fields- Instructions: Use only the one compass that you construct. Just move it around the central metal wire. Reverse the flow of electric current by reversing the leads of the battery.

Our objective will be to make a very simple magnet which will allow us to find the north and south poles of the earth.

What you will need:

  A sewing needle or straight pen roughly an inch in length.

  A small bar magnet or a refrigerator magnet.

  A small fishing cork (or a piece of a larger one)

  A small cup or saucer of water to float the cork and needle.

How to make the compass:

The first step is to magnetize the needle or pin. You can do that by "stroking" it with the magnet. Holding the magnet the same way each time, place it in contact with the pin and run it down the length of the pin.  Lift the magnet up, return to the starting point, and stroke it again. Always stroke the pin (needle) in the same direction with the same part of the magnet. CLICK HERE TO SEE ANIMATION ON HOW TO DO THIS. This stroking process causes some of the iron molecules in the pin to become magnetized and we will use that feature for our compass.

Next, test float the cork to see how it sits in the water.  Then force the needle all the way through the cork so that it sticks out both sides above the water. Because the magnet you used was probably not all that strong, the smaller the piece of cork, the better it will be. But if you cut the cork be careful not to cut yourself instead.  A small circular piece of cork cut off a fishing cork or wine bottle will work well.

Now float the cork and pin in the water again. The needle should be out of the water and approximately parallel to the surface. Watch what happens as the disturbances in the water settle down. The pin will slowly begin to turn until it is pointing along the north/south axis of the earth. The manner you held the bar magnet will determine whether the pin's head or tip points to the north pole, but once you know you then have a magnet that can be used anywhere you can find a puddle of water deep enough to float the cork.

The earth's magnetic field is not all that strong, but so long as you keep the weight of the pin/cork combination low, and let it move freely on the surface of the water, it will be able to align itself with the earth's magnetic field.

How compasses work

Questions/answers about the earth's magnetic field

d. Relate electric currents to magnetic fields and describe the application of these relationships, such as electromagnets, electric current generators, motors and transformers
e. Design and interpret simple series and parallel circuits
f. Define and calculate power, voltage differences, current, and resistance in simple circuits

g. Recognize conservation of charge and energy and apply these to simple circuits

 

Describe and provide examples of electrostatic and magnetostatic phenomena

Lessons on Electrostatics

Summary (pdf)

More details (pdf)

Electrostatic phenomena-gif animations plus explanations- Induction of charges

Inducing a positive charge on a sphere

Charging a two-sphere system by induction

Charging an Electrophorus by induction using a negatively-charged object

Charging an Electroscope by induction using a negatively-charged balloon

Grounding a positively-charged Electroscope

Grounding a negatively-charged Electroscope

 

 

Lessons on Electricity

Current

Electrical Potential Difference

Ohms' Law

Electrical Circuits and Kirchoff's Laws

Series and Parallel Circuits

Electrical Power and Energy

 

Magnetostatic phenomena
A brief review of ferromagnetism: Iron, cobalt, nickel (and various alloys of these materials) are termed ferromagnetic materials. Ferromagnetic materials are materials which can be permanently magnetized upon application of an external magnetic field. This external field is typically applied by another permanent magnet, or by an electromagnet.
Paramagnetic materials are attracted toward magnets, but do not become permanently magnetized.
Diamagnetic materials are repelled by magnets, but do not become permanently magnetized. If the temperature of a ferromagnetic material is raised past a certain point (called the Curie temperature) the material abruptly loses its permanent magnetization and becomes simply paramagnetic.
Ferromagnetic materials are the most magnetically active substances in the world, and so they have very high magnetic susceptibilities, ranging from 1000 up to 100,000. These materials are made of atoms with permanent dipole moments (see geomagnetism link below), and when these materials form solids by exchanging electrons to make chemical bonds, something special happens. If the atoms are of the right type and if the bond lengths are right, the electrons discover that they can place the system in a state of lower energy by having neighboring atomic dipole moments aligned with each other. (This sentence probably makes no sense to you, but it is the best we can do. That's just the way quantum mechanics is.) If the entire sample were to be made of aligned dipoles, however, a strong magnetic field would be created, and this would be a state of high energy. So the system compromises. It makes microscopic regions in which billions of dipoles are aligned, satisfying the demands of most of the electron bonds. But the alignment directions of the separate regions are random throughout the sample, making a very weak net magnetic field. These regions are called magnetic domains, and their behavior gives ferromagnetic materials their distinctive properties.
Diamagnetism: A diamagnetic material is one whose atoms have no permanent dipole moment. When they are placed in a strong magnetic field, Lenz's law acts on the orbiting electrons and causes an atomic dipole moment to appear directed opposite to the direction of the magnetic field. The effect is very weak, but its effect, roughly, is to cause repulsion where other forms of magnetism give attraction.
Geomagnetism - Click on Chapter 1 and read introductory page and drawing at the top of the next page (Figure 1.1) describing dipole moments.
Pictures of Magnetic domains: Read intro and scroll down to see three pictures: left picture is nonmagnetic, middle is beginning magnetic domains form, right picture is strong magnetic domains (formation of magnetic domain bubbles). High energy and highly magnetic.
Magnetism and magnetic fields
Earth's Magnetic Field
Nonmagnetic materials
Permanent magnets

 

 

Relate electric currents to magnetic fields and describe the application of these relationships, such as electromagnets, electric current generators, motors and transformers

USE ADDITIONAL URL'S ON STUDY GUIDE

Electricity- Brief Summary

Atomic View of charges

Electric current

Electric potential

Electric energy and electric potential

Electric Field

Electric force field

Charges and fields

 

Behavior of charged particles in an electric field-

Use modified activity on study guide- you may also perform the one below

Activity: When you access the link above you will be adding a single positive charge into the left side of the white square at the top of the page

  • Click add button
  • Move the slider at the bottom of the applet to the far right to select a strong positive charge
  • Click once on the left side of the applet. A RED, positively charged sphere will appear.
  • Move slider to the far left side to select a strong negative charge
  • Click once on the right side of the applet. A BLUE negatively charged sphere will appear
  • Click on the button "potential"... the potential force field appears.
  • With the slider to the far left, click "Movil" once... a blue negatively charged electron will begin moving toward the force field.
  • Move the slider to the far right and click "Movil" once... a red positively charged particle will begin moving into the force field.
  • OBSERVE HOW THE MOVING CHARGES BEHAVE AS THEY GO INTO FIELD
  • ANSWER THE FOLLOWING QUESTION: (5 points- required): How did the positive and negative moving charges behave in the force field on the applet?
  • If you wish to try other things, click refresh on the browser page and perform your exploration.

 

 

Electromagnetism

Magnetic Force on Moving Electric Charge

Magnetism from electricity

Force on a current-carrying wire

Force on two parallel wires- experiment

Electric motor

Speaker/Microphone

Ferromagnets

Electromagnetism, Inductors and Transformers

 

 

Design and interpret simple series and parallel circuits Define and calculate power, voltage differences, current, and resistance in simple circuits

 

Use modified activity on study guide- Level III

Voltage, Resistance and Current

Electric Power

Understanding and Calculating Series Circuits

Understanding and Calculating Parallel Circuits

Resistance in a Parallel Circuit

Identifying simple electric circuits

Identify the two types of simple electric circuits.

Electrical Safety

 

 

Recognize conservation of charge and energy and apply these to simple circuits

Conservation of Energy- definition

Ohms, Voltage and Current laws and conservation of charge and energy

 

Detailed application of concepts above:

1. Nuclear Physics

2. Atomic Physics

 

 

 


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