Define Electric Flux and Electromotive Force (EMF)

In Class 12 Physics, two very important quantities you will study in electromagnetism are Electric Flux and Electromotive Force (EMF). Despite their names, flux is not a liquid flow, and EMF is not a mechanical force.

Question (Click to Flip)

Define electric flux.

Answer

Electric flux is defined as the total number of electric field lines passing perpendicularly through a given surface area in an electric field.

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Key Facts

Electric Flux: Number of electric field lines crossing an area.

Flux Unit: N·m²/C.

EMF: Maximum voltage of a battery when no current is drawn.

EMF Unit: Volt (V).

Both Flux and EMF are Scalar quantities.

1. Electric Flux (ΦE) Definition

Electric Flux is defined as the total number of electric field lines passing normally (perpendicularly) through a given surface area.

It gives a measure of the strength of the electric field crossing a specific area.
Formula: ΦE = E · A = EA cos(θ) (Where E is Electric Field, A is Area vector, and θ is the angle between them).
SI Unit: Newton metre squared per Coulomb (N·m²/C) or Volts-metre (V·m).
Type: It is a Scalar quantity.

2. Electromotive Force (EMF) Definition

Electromotive Force (EMF) is defined as the maximum potential difference between the two terminals of a battery or cell when no current is flowing through the circuit (an open circuit).

Alternatively, it is the work done by a battery to move a unit positive charge once entirely around a complete circuit.
Formula: ε = W / q (Work done / Charge)
SI Unit: Volt (V) or Joules/Coulomb (J/C).
Misnomer: It is called a 'force' due to historical reasons, but it is actually a measure of potential energy per unit charge, not a force.

Questions and Answers

Define electric flux.+

Electric flux is defined as the total number of electric field lines passing perpendicularly through a given surface area in an electric field.

What is electromotive force (EMF)?+

Electromotive force is the maximum potential difference between the two electrodes of a cell when the circuit is open (no current is drawn from the cell).

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