PHYSICS: ELECTRICITY

PHYSICS: ELECTRICITY

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Overview

• Electricity is an extraordinarily versatile source of energy
  
• Electricity is the backbone of modern industrial society
  
• The phenomenon of electricity includes concepts such as 
  
  • Electric charge: a property of subatomic particles that determines their electromagnetic interactions
    
  • Electric current: a movement or flow of charged particles
    
  • Electric field: influence of charged particles on other charged particles in the vicinity
    
  • Electric potential: capacity of an electric field to do work
    
  • Electromagnetism: interaction between electric and magnetic fields
    

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TIMELINE OF EARLY DISCOVERIES/INVENTIONS

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BASIC ELECTRICAL COMPONENTS

1. Resistors
   1. Resistors are materials that resist the flow of current through them
   2. They dissipate energy in the form of heat
   3. Ohmic materials are those materials whose resistance remains constant over a range of temperatures and currents. Non-ohmic materials have resistances that change
      
   4. The unit of resistance is Ohm
2. Capacitors
   1. Capacitors are devices that store electric energy in the form of electric charge
   2. They usually consist of two conducting plates separated by a thin insulating layer
   3. Capacitors block steady state current i.e. DC current
   4. The unit of capacitance is Farad
3. Inductors
   1. Inductors are conductors that store energy in a magnetic field, which is produced in response to an electrical current
   2. Inductors allow steady current, but oppose rapidly changing currents
   3. The unit of inductance is Henry
4. Transformers
   1. A transformer is a device that transfers electrical energy from one circuit into another
   2. This transfer occurs through inductively coupled conductors, where varying current in one circuit creates a varying magnetic field (and hence voltage) in the other circuit
   3. Transformers can be used to step-up or step-down voltages from high voltage transmission lines to appliances in homes

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ELECTRICITY IN NATURE

1. Electric shock
   1. A voltage applied to the human body causes an electric current through the tissues
   2. In general, greater the voltage applied, greater the current passed through the tissues
   3. Voltages 100-250 V can be lethal in humans, although as low 32V has been lethal sometimes. Lethality increases dramatically beyond 250V
      
   4. If the current is sufficiently high, it can cause muscle contractions, fibrillation of the heart and tissue burns
   5. DC tends to cause continuous muscle contractions making the victim hold on to a live conductor, thereby increasing risk of tissue burn
   6. AC tends to interfere with heart function, increasing risk of cardiac arrest
   7. AC at high frequencies, causes current to travel on the surface due to skin effect. This results in severe burn but is usually not fatal
2. Electrical phenomena
   1. Touch, friction and chemical bonding are all due to interactions between electrical fields on the atomic scale
   2. The Earth’s magnetic arises from a natural dynamo of circulating currents in the planet’s core
   3. Piezoelectric crystals like quartz and sugar generate electric current when subject to mechanical pressure
   4. Electric eels detect and stun their prey via high voltages (500 V) generated from muscle cells called electrocytes
   5. Electrical currents, called Action Potential, are used for nervous system communication in all animals, including humans

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JOHAR