Electrical Power, Work, and the Electron Volt

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  • Ohm’s Law postulates that current is directly proportional to applied voltage, and inversely proportional to resistance. This is expressed as:

Current = Voltage/Resistance, or I=V/R, which can be transposed to get;

V=IR

R=V/I

NB: Volts push Amps through Ohms.

  • Electrical power is measured using the unit of measurement called the Watt (W). 1 W(att) is equal to work done by 1V to move 1C of electrons for 1 second (s), i.e 1W = 1VC/s. Also, 1C/s = 1A, therefore 1W=1VA. This means that power can be calculated as:

Power (P) = Voltage (V) × Current (I)

If V=IR is substituted for Voltage, then P = IR × I = I2R.

If I=V/R is substituted for Current, then P = V × V/R = V2/R.

  • 1 horsepower (HP) is equal to 746 Watts.
  • Work can be described as power used for a specific time period, and thus work can be calculated as:

Work = Power × Time (in seconds), which means that,

Power = Work/Time.

  • The above formula shows that if 1W of power is used for 1 second, then the work done is: Work = 1W × 1s = 1W.s (or 1 Joule). The Joule (J) is the unit of measurement of work.
  • In the circuit, work is done by the ordered flow of electrons, and the work done by these electrons is measured using the electron volt (eV), which can be calculated as follows:

1 Joule = 1W used for 1 second = 1VC/s × 1s = 1VC (Volt-Coulomb).

Because 1C is 6.25 × 1018 electrons, then 1 Joule = 6.25 × 1018 electron-volt (eV).

  • Electricity providers charge for work done using their electricity, and this is charged as Kilowatt-hours (kWh), which makes it a key unit of energy rating. 1 kilowatt-hour is equal to:

1 kWh = 1000 watt × 3600 seconds (or 1hour) = 3.6 × 106 Joules = 3.6 megaJoules = 3.6MJ.

  • In terms of electron-volts, 1kWh = 3.6 × 106 × 6.25 × 1018 = 2.25 × 1025 eV.
  • Electric shock is the sudden involuntary contraction of skeletal muscles caused by current flow through the body after a person touches a live wire hence completing a circuit. It can cause pain and severe burns if one touches a high-voltage wire. The human body has a resistance value range of 10-50 kΩ. At 9 milliAmpere (mA) for an adult male and 6mA for an adult female, the electric shock causes significant discomfort to cause one to release the live wire.
  • Planet earth can be used as a conductor. The circuit path where the earth is used to connect the load to the power source is called the earth return.
Using a bare hand to touch an uninsulated conductor that is transmitting high voltage can result in catastrophic electric shock

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