Electricity and Magnetism Notes and study guide

 

 

 

Electricity and Magnetism Notes and study guide

 

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Electricity and Magnetism Notes and study guide

Electricity and Magnetism Notes
Electric Charge

  1. Protons and electrons both have the property of charge.  Recall that protons are positive and electrons are negative.
  2. A force of attraction exists between things that have opposite charges.
  3. A force of repulsion exists between things that have same charges.

Electric Field

  1. An electric field extends outward through space from every charged particle.  As things move toward each other the charge may move from one object to another.
  2. The electric field is strongest near the charged particle. 

Static Electricity

  1. Because electrons can move freely things can become either positively or negatively charged.  Charge is only being transferred from one object to another.  This is called the Law of Conservation of Charge.
  2. Static electricity – is the buildup of electric charges on an object.

Methods of Charging

  1. Friction – when two objects are rubbed together.  Example:  balloon on your hair.
  2. Conduction – the direct contact of objects.  Example:  plugging something in.
  3. Conductors – allow electricity to go through easily
  4. Insulators – do not allow it to move through.
  5. Induction – the jumping of electricity from one object to another.  Example:  a negatively charged rubber rod can pick up tiny pieces of paper.

 

Electric discharge – the loss of static electricity as electric charges move off
an object.  Sometimes slow and quiet, or rapid with a spark of light, shock,
or crackle of noise. Example:  lightning or a simple static shock

Circuits

  1. A circuit – is formed when a wire is connected to the terminals of a source forming a complete path.
  2. Electric current – the amount of charge that passes a given point per unit of time.
  3. The symbol for current is I

Things to know…

  1. Georg Simon Ohm established the relationship between electric current and potential difference.  Ex. 8 v battery vs 4 v battery.
  2. Resistance – R opposition to the flow of electric charge (example: copper low: iron high)  The unit to measure resistance is the ohm
  3. Ohm’s law – the current in a wire is equal to the voltage divided by resistance

                                I = V/R
Superconductor

  1. Superconductor – low temperatures, resistance is zero.  Must be kept extremely cold.
  2. A phenomenon observed in several metals. When these materials are cooled to temperatures near absolute zero, using liquid nitrogen, they have no electrical resistance.  This means they can carry large amounts of electrical current for long periods of time without losing energy as heat.
  3. Superconducting loops of wire have been shown to carry electrical currents for several years with no measurable loss

Another property of a superconductor is that magnetic fields can't penetrate it.  It has implications for making high speed, magnetically-levitated trains… kinda neat huh…

Current direction

  1. DC (direct current) – electrons always flow in the same direction. Example: batteries
  2. AC (alternating current) electrons move back and forth, reversing direction regularly.  (example: current in home changes direction every second 120x)

Types of Circuits

  1. Electric circuit – consists of a source of energy; a load; wires, and a switch.
  2. Sources:  battery, thermocouple, photocell, or electric generator
  3. Load – uses the electricity

Series vs Parallel

  1. Series circuit – only one path to take; if any part goes out the whole thing goes out. Example: old Christmas lights
  2. Parallel circuit – separate paths.  Example: circuits in homes.
  3. Fuses – protect against too much current flow
  4. Circuit breakers – like fuses but do not burn out.

Power

  1. Electric Power – a measure of the rate at which electricity does work or provides energy.  Measured in watts.
  2. Power = voltage x current
  3. Energy = power x time

Electric Safety

  1. Never handle when wet or near water
  2. Never run wires under carpet
  3. Never overload circuits
  4. Repair worn out wires
  5. Put nothing in electric sockets that does not belong
  6. Never go by fallen wires or power lines
  7. In lightning storms get down to the ground by crouching down low and stay away from trees.
  8. Safest spot in a lightning storm is inside a car.

 

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