# Electronic – Double-Subscript Notation for Voltages

basicmathvoltage

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?

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 \$$ Link to reference: Voltage notation conventions