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Electromagnetism

9th grade physics

Electrostatics

What is the electric field?

Electric current: The water flow analogy

Currents and DC circuits (with many Word documents)

  1. What is an Electric Circuit? (PhysicsClassroom.com)
  2. Requirements of a Circuit (PhysicsClassroom.com)
  3. Electric Current (PhysicsClassroom.com)
  4. Power: Putting Charges to Work (PhysicsClassroom.com)
  5. Common Misconceptions (PhysicsClassroom.com)
  6. Fuses and ground fault circuit interrupters (GFCI)
  1. Circuit Symbols and Circuit Diagrams (PhysicsClassroom.com)
  2. Series and Parallel circuits
  3. Series Circuits – finding equivalent resistance
  4. Parallel Circuits – finding equivalent resistance
  5. Series & Parallel together – finding equivalent resistance

PhET Circuit construction kit lab

Power (electrical)

What is magnetism

The electromagnetic spectrum

Magnetism and electricity: the connection between them

 

12th grade physics

Light is an EM field

Rods and cones: perception of color

Sunsets & the green flash (refraction of light)

Equipotential Lines and topographical maps

Types of magnetism

Related articles

Radar

What kinds of radiation cause cancer

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I. Magnetism is the phenomenon behind:

  • MRIs – magnetic resonance imagers, useful in medicine.

  • Computer disk drives, audio cassettes, and floppy disks

  • automobile alternators  (charge the battery, and power the electrical system when the engine is running)

  • electric motors

  • generating electricity

  • Speakers

    Maglev (magnetically levitating trains)

II. Electricity is the key phenomenon behind:

  • Refrigerators, dishwashers, dryers, washing machines, microwave ovens

  • Cell phones, tablets, computers, videogame consoles, chargers

  • Lamps, light bulbs, streetlights

  • some water heaters

  • Electric cars, electric trains & trolleys

III. Ultimately, magnetism and electricity turn out to be different aspects of the same thing (the electromagnetic field)

IV. Table of contents

What is the electric field?

Electrostatics

Electric current: The water flow analogy

Currents and DC circuits (with many Word documents)

TBD: Magnetism (was: em-waves-and-light)

IV. On Quora, Mark Eichenlaub writes:

…the history of electromagnetism is one of unification. Over and over, different ideas about how things work were subsumed into the same theoretical framework…. Electromagnetism is an example of a field theory, the central object of study in theoretical physics.

A “field” means that at any point in space and time, there’s an electric and magnetic vector there. These fields pervade all of space – they are in the room around you right now, and in outer space, even within you…

We don’t have a mechanical picture of what the field is, or why it is a certain way. It’s not like waves in the water or anything like that. It just exists, but we do have mathematical rules that describe how it works….

Michael Faraday investigated things like the way a wire carrying electric current deflects a compass needle. His crowning achievement was to discover that changing magnetic fields create electric fields, a phenomenon called induction.

James Clerk Maxwell looked at all that, sat down with pen and papers, and mathematically described Faraday’s results in a complicated set of differential equations, importantly including the idea that changing electric fields would create magnetic fields, completing the symmetry between the two.

James Clerk Maxwell animated GIF

When Maxwell finished his theory, he discovered that it allowed waves of electromagnetism to fly off at high speed – when he calculated the speed, it turned out to be the speed of light.

Experiments with radio waves soon verified that light was nothing more than a special form of electricity and magnetism.

You can think of it as if we had been studying the way hot air balloons and airplanes and things work, and so were thinking about the dynamics of air. In the process, we develop equations for air, and figure out that sound is just waves moving through the air. The theory of sound and the theory of airplanes are actually the same theory, even though they don’t seem very similar. That’s roughly what happened for light, except that unlike for sound, no one expected it. (Or at least it wasn’t obvious beforehand.)

Maxwell’s equations describe how electric and magnetic fields work, but those fields need to interact with matter – that happens via electric charge.  Charge is an innate property of matter…

What exactly is the relationship between electricity, magnetism, and light?

We keep talking about the electromagnetic field. What exactly is a “field” anyways? How do understand what one is? See here: What are fields?

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The electromagnetic force is the force of nature behind electric fields, magnetic fields, and light.

It is one of the four fundamental forces in nature.

“Electromagnetism” is a compound form of two Greek terms:

ἤλεκτρον, ēlektron, “amber”, and μαγνῆτις λίθος magnētis lithos, which means “magnesian stone”, a type of iron ore.

The electromagnetic force plays a major role in determining the internal properties of most objects encountered in daily life. Ordinary matter takes its form as a result of intermolecular forces between individual molecules in matter. Electrons are bound by electromagnetic wave mechanics into orbitals around atomic nuclei to form atoms, which are the building blocks of molecules.

This in turn governs chemistry, which arise from interactions between the electrons of neighboring atoms. This in turn is determined by the interaction between electromagnetic force and the momentum of the electrons.

The theoretical implications of electromagnetism, in particular the establishment of the speed of light based on properties of the “medium” of propagation, led to the development of special relativity by Albert Einstein in 1905.

Learning Standards

Massachusetts 2016 Science and Technology/Engineering (STE) Standards

HS-PS2-4. Use mathematical representations of Newton’s law of gravitation and Coulomb’s law to both qualitatively and quantitatively describe and predict the effects of gravitational and electrostatic forces between objects.
HS-PS2-5. Provide evidence that an electric current can produce a magnetic field and that a changing magnetic field can produce an electric current.
HS-PS2-9(MA). Evaluate simple series and parallel circuits to predict changes to voltage, current, or resistance when simple changes are made to a circuit
HS-PS3-1. Use algebraic expressions and the principle of energy conservation to calculate the change in energy of one component of a system… Identify any transformations from one form of energy to another, including thermal, kinetic, gravitational, magnetic, or electrical energy. {voltage drops shown as an analogy to water pressure drops.}
HS-PS3-2. Develop and use a model to illustrate that energy at the macroscopic scale can be accounted for as either motions of particles and objects or energy stored in fields [e.g. electric fields.]
HS-PS3-3. Design and evaluate a device that works within given constraints to convert one form of energy into another form of energy.{e.g. chemical energy in battery used to create KE of electrons flowing in a circuit, used to create light and heat from a bulb, or charging a capacitor.}
HS-PS3-5. Develop and use a model of magnetic or electric fields to illustrate the forces and changes in energy between two magnetically or electrically charged objects changing relative position in a magnetic or electric field, respectively.

SAT Subject Area Test: Physics

Electric fields, forces, and potentials, such as Coulomb’s law, induced charge, field and potential of groups of point charges, and charged particles in electric fields
Capacitance, such as parallel-plate capacitors and time-varying behavior in charging/ discharging
Circuit elements and DC circuits, such as resistors, light bulbs, series and parallel networks, Ohm’s law, and Joule’s law
Magnetism, such as permanent magnets, fields caused by currents, particles in magnetic fields, Faraday’s law, and Lenz’s law

Learning Standards: Common Core Math

  • CCSS.MATH.CONTENT.7.EE.B.4  Use variables to represent quantities in a real-world or mathematical problem, and construct simple equations and inequalities to solve problems by reasoning about the quantities.
  • CCSS.MATH.CONTENT.8.EE.C.7  Solve linear equations in one variable
  • CCSS.MATH.CONTENT.HSA.SSE.B.3  Choose and produce an equivalent form of an expression to reveal and explain properties of the quantity represented by the expression. (including isolating a variable)
  • CCSS.MATH.CONTENT.HSA.CED.A.4  Rearrange formulas to highlight a quantity of interest, using the same reasoning as in solving equations. For example, rearrange Ohm’s law V = IR to highlight resistance R.
  • http://www.corestandards.org/Math/

Common Core State Standards (Inverse-square law)

CCSS.Math.Content.7.RP.A.2a ( Grade 7 ): Decide whether two quantities are in a proportional relationship, e.g., by testing for equivalent ratios in a table or graphing on a coordinate plane and observing whether the graph is a straight line through the origin.
CCSS.Math.Content.7.RP.A.2c ( Grade 7 ): Represent proportional relationships by equations.
CCSS.Math.Content.7.RP.A.3 ( Grade 7 ): Use proportional relationships to solve multistep ratio and percent problems.

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