Electronic – Double-Subscript Notation for Voltages


I have read from some book that: "The voltage quantity symbol V sometimes has subscripts to designate the two points to which the voltage corresponds. If the letter a designates one point and b the other, and if W joules of work are required to move Q coulombs from point b to a then, \$V_{ab}=\frac{W}{Q}\$. Note that the first subscript is the point to which the charge is moved"

While Wikipedia (http://en.wikipedia.org/wiki/Double_subscript_notation) says: "\$V_{CB}\$ means the "\$V\$" from \$C\$ to \$B\$."

Can you help me with the true meaning of the first subscript?

Best Answer

I've taught it this way before to give a mental picture of double subscript notation.

\$V_{ab}\$ is the voltage measured by a voltmeter when the red (positive) lead is connected to node a and the black (negative) lead is connected to node b.

A single subscript, \$V_a \$, is measured with red to node a and black to node 0 ("ground").

It then follows that: \$V_{ab} = V_a - V_b \$

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Link to reference: Voltage notation conventions

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