Voltage Across And Current Through

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To begin with, Voltage is the potential energy across parts of a circuit while Current is the moving charges through parts of a circuit.

  • Voltage
  • Current
  • Wattage (voltage times current)

Therefore, it is very easy to measure voltage. You simply set a multimeter to measure voltage and place the probes across any 2 parts of a circuit you want to know the voltage of.

Current however has to also flow through the meter to be measured. Therefore, the circuit must be open. Make sure to set the correctly set the meter to measure more than the largest possible amount of current. Finally, bridge the gap with the meter probes.

Primary dangers of…

  • High voltage – Results in unwanted current. For instance, if you touch a household electrical socket and get a voltage running across your chest, the resulting current may stop your heart. However, you can touch the terminals of a nine volt battery however you want and your body’s electrical resistance will limit current well below what is needed to affect your heart activity. Some components will be instantly fried if enough voltage forces current through them.
  • High Current – High amounts of current will result in heat. Too much heat will quickly destroy components not able to dissipate the wattage (voltage in volts times current in amps – P = VI) demanded of them. Worse case scenario is that a hot item, such as a metal tool with a 12V car battery (capable of providing very high currents) across it, can cause nasty burns to you and even weld metal together. Some components can create gas and explode due too much current.  Fuses are selected so that they are the most current damage sensitive component of a circuit.

Common component voltage vs current relationship

  • Resistor
  • Diode/LED
  • Capacitor

First component we will analyse is the resistor. Resistors and other resistance based components have a linear relationship between voltage and current. In electronic circuits, the higher resistance components are absorbing the most voltage from the power supply. In doing so, they create a lot of heat (a form of electrical power). Thus, their Wattage rating (ability to dissipate power/heat) should be at least twice what is expected of them. Always remember. Power in Watts is the voltage, in volts, across a component times the current in Amps, going through the component.  Power equals voltage times current. P = VI.

Second component we are analyzing is the semiconducting diode. Primarily the rectifier and LED (light emitting diode) versions. Diode components conduct better when they are forward biased than reverse biased. Rectifier diodes in particular, are made to block a lot of voltage when wired reverse biased. Whereas they only block a small amount of voltage when it applied to them forward biased.

Third component we are analyzing is the capacitor.


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