Current, Voltage, and Resistance Basics

Voltage

• Voltage is the "pusher" of electric charge (electrons) that causes current to flow.
• Voltage sources include batteries, generators, and outlets.
• Symbol for voltage is V, and its unit is Volts (V).
• Alessandro Volta, an Italian physicist, invented the electrochemical cell (battery) in 1800.

Current

• Current is the flow of electric charge (electrons) within a conductor.
• Charge will only flow if there is a voltage source (potential difference).
• Symbol for current is I, and its unit is Amps (A).
• André Ampère, a French physicist, is one of the main discoverers of electromagnetism.
• The SI unit of measurement for electric current, the ampere, is named after him.
• Effects of current on a person:
  • 0.001 A: Can be felt
  • 0.005 A: Painful
  • 0.010 A: Involuntary muscle spasms
  • 0.015 A: Loss of muscle control
  • 0.070 A: If through the heart, serious injury, likely fatal if it lasts more than 1 second

Resistance

• Resistance opposes the "push" from the voltage source.
• Resistance affects the speed of the current.
• Symbol for resistance is R, and its unit is Ohms (Ω).
• Georg Ohm, a German physicist, determined that there is a direct proportionality between the voltage applied across a conductor and the electric current.
• Ohm's Law states that Voltage (V) is equal to Current (I) multiplied by Resistance (R).

Ohm's Law and Relationships

• If voltage in a circuit increases, the current will increase (direct proportional relationship).
• If voltage in a circuit decreases, the current will decrease (direct proportional relationship).
• If resistance in a circuit increases, the current will decrease (inversely proportional relationship).
• If resistance in a circuit decreases, the current will increase (inversely proportional relationship).

Temperature Variation of Resistance

• The resistance of a material can change with temperature changes.
• The equation 𝛒=𝛒o(1+ 𝛂𝝙T) can be used to calculate the resistance at different temperatures.

Devices Measuring Currents and Voltages

• Measuring currents and voltages can alter the circuit.
• Devices used to measure currents and voltages must be carefully designed to minimize their impact on the circuit.