EMFs and PDs

2-minute read
Table of Contents

Electromotive force and potential difference are mentioned when speaking about voltages in a circuit.

Hold a focus!

1) Electromotive force is associated with devices that add power to the circuit (a.k.a. active devices).

  1. False
  2. True

Electromotive force

Electromotive forces cause the potential difference in the circuit. The electric potential at one terminal is made to be greater compared to the other terminal.

EMF is responsible for taking the charge up the proverbial hill.

Potential difference

This is the drop in electric potential between two points. When two points are connected via a conductor and there is a potential difference between the two points, a current flows between the two points in order to balance the potentials between the two points. If there is no PD, there is no current.

PD is when the charge rolls down the hill.

Differences between EMF and PD

Table 1 Table showing the differences between electromotive forces and potential differences
Aspect EMF PD
Definition Max voltage available from a power source Voltage drop across a device
Associated devices Active devices Passive devices
Examples of devices Batteries, generators Resistors, motors, heating elements
Effect of resistance Not affected by resistance Changes with resistance
Energy in circuit Energy is gained Energy is lost
Change in electric potential Increases potential Decreases potential
Current Present regardless of current No current, no PD

electricity
Resistivity
← Drift Velocity
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