Electric Flux and Faraday Tubes

Electric Flux and Faraday Tubes

Consider a small closed curve in an electric field (Figure given below)

If we draw lines of force through each point of this closed curve, then we get a tube as shown in the figure. It is called the tube of the electric flux. It may be defined as the region of space enclosed within the tubular surface formed by drawing lines of force through every point of a small closed curve in the electric field.

Since lines of force end on conductors, the two ends of a flux tube will consist of small area ds1 and ds2 on the conductor surfaces. If surface charge densities over these areas are σ₁ and − σ₂, then charges at the two ends of the flux tube will be σ1 ds₁ and − σ₂ ds₂. These charges are assumed to be always equal but opposite to each other. The strength of a flux tube is represented by the charge at its ends.

A unit tube of flux is one in end charge is one unit of charge.
In the S.I. system of units, one such tube of flux is supposed to start from a positive charge of one coulomb and terminate on a negative charge of the same amount.

A unit tube of flux is known as Faraday tube. If the charge on a conductor is ± Q coulombs, then the number of Faraday tubes starting or terminating on it also Q.

The number of Faraday tubes of flux passing through a surface in an electric field is called the electric flux (or dielectric flux) through that surface. Electric flux is represented by the symbol ψ. Since electric flux is numerically equal to the charge, it is measured in coulombs.

Hence,

ψ = Q coulombs

tubes of flux = Q and lines of force = Q/ε

What is electric flux?

Electric flux, property of an electric field that may be thought of as the number of electric lines of force (or electric field lines) that intersect a given area. Electric field lines are considered to originate on positive electric charges and to terminate on negative charges.

What is the difference between electric field and electric flux?

Electric field is the electric strength at the point due to charge (q). Electric flux is the imaginary field lines produced from +q and terminated at -q charges.

The electric field is defined as the electric force per unit charge. The electric flux is defined as the electric field times the normal area vector.

What is the formula of electric flux density?

The electric flux density, D, is then equal to the electric flux emanating from the charge, q, divided by the area of the sphere. coulombs per square meter; where the area is perpendicular to the lines of flux. (One coulomb is equal to the magnitude of charge of 6.25 X 10¹⁸ electrons.)

What is the symbol of electric flux called?

We represent the electric flux through an open surface like S1 by the symbol Φ. Electric flux is a scalar quantity and has an SI unit of newton-meters squared per coulomb (N⋅m2/C).

Read article – Units of Resistivity

Visit NCERTplanet.com for NCERT solutions and Textbook downloads