Circuit Theory

Basics

VOLTAGE

Voltage:

Voltage is

  • how much work is done in moving a unit charge from infinity to a point against the influence of electric field.
  • Voltage = Work-done per unit charge$$V (t)=\frac {dW}{dq}$$

Unit:

    • volt (V)
    • Joules/Coulomb (since work-done per unit charge)
    • Also, Work done = Force × distance, hence unit of voltage can be Nm/C (Newton – metre / Coulomb)

The definition of voltage can vary based on the type of device across which the voltage is measured. (e.g) In a voltage source, voltage means how much electrons it can attract but in a resistor, voltage means how much electrons it can resist.

Practice Question

The unit of voltage is
a) volt
b) J/C
c) Nm/C
d) All the above 

Correct Answer: Option D

Types of Voltage:

Voltage
Voltage
DC
DC
AC
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DC Voltage:

  • Magnitude and polarity will be constant over time.
  • DC voltage has constant polarity.
  • DC has zero frequency.
time     
time     
V
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AC Voltage:

  • Magnitude and polarity will vary with respect to time.
  • AC voltage changes its polarity continuously on its own.
  • AC has frequency ranges from $1$ Hz to infinity.
time     
time     
V
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Voltage Measurement:

Voltage can be measured by using a voltmeter.