Methods of Producing EMF

Methods of Producing EMF

1. Chemicals

   • Battery contents
     • two dissimilar metals and an electrolyte
   • Electrode
     • Part of the device in which electrons either enter or leave
   • lead-acid battery example
     • has two plates. one lead and one lead dioxide
       • after being immersed in a sulphuric acid electrolyte. Lead combines with the acid to create S04
         • This is chemical process that a voltmeter picks up on
   • Fuel cells are another example of chemical batteries
     • chemical reaction is harnessed to generate a current
       • Chemical oxidation is capable of creating electron flow as well as the lead acid example
   • DC Voltage is produced

2. Heat

   • Dc Voltage is produced
   • Current that flow in a thermocouple
     • Thermocouple called the junction
       • Current is still present as long as two Junctions still have different temperatures
         • Seebeck Effect
           • name of scientist to discover that emf could be generated this way
     • Reverse hot and cold junction, current flow will reverse direction
     • Selection of metals also affects the magnitude of the emf
   • Change in temp. produces a change of voltage
     • Can be found in heating controls or power source for relays

3. Pressure

   • DC Voltage
   • piezoelectricity
     • Phenomenon found when certain materials with pressure applied to them, generate electricity
       • Electric Lighter
         • Press button makes spring loaded hammer to hit crystal. High voltage is caused creating a spark to ignite gas
     • is the interaction between Coulomb forces and elastic forces in a cell when suubjected to a mechanical force
     • Opposite effect called converse piezoelectric effect
       • found in analog watch movements
   • 1cm cube of quartz + 500lb of force can produce 12 500V

4. Light

   • DC voltage
   • solar cells typically used for light
     • Have very long life
     • very expensive
     • Size of a solar cell hasn't changed in 30 years
   • photoelectric effect
     • Electrons are dislodged from atoms under the influence of light
   • no moving parts, no noise, no waste or pollution
   • solar cell 1*2cm2 has a max output of 50mA at 0.5V

5. Magnetism

   • created when a conductor moves through a magnetic flux
     • called electromagnetic induction
       • produces almost all electricity used in homes, business and industry
   • Faraday's Law of Induction
     • States the magnitude of voltage induced is proportional to the rate the conductor cuts the lines of force
       • if number of lines of force is increased, magnitude of induced voltage is increased
     • 3 factors to affect induced voltage
       • flux density or strength of the field
       • length of conductor within the magnetic field
       • rate at which lines of force are cut by the conductor
   • generator uses magnetic induction to induce emf
     • Components; magnetic field and wire loops or coils

6. Electrostatics

   • Daily experience is often generated through tribocharging
     • the separation of electrical charges that occur when two matieals are brought into contact, then separated
       • called friction
   • generated by the molecular, unbalanced construction of non-conductive insulators such as plastics and paper
   • Van de Graaff
     • generator that has the ability to produce extremely high voltages
       • ex: X-rays

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