3.2 Definition of terms 41 9 Short circuit: the connection between nodes 4 and 5 is made with a piece of
wire having virtually no resistance and is called a short circuit. The
connection between nodes 5 and 6 is also a short circuit so that nodes 4, 5,
and 6 are identical nodes and the circuit may be redrawn as shown in Fig. 3.2.Figure 3.2
R1 i o R2 I
1~.~34,5,6
In a circuit diagram it would be neater to draw the circuit of Fig. 3.1.
9 Open circuit: if the resistor R 1 were removed from the circuit then there is
said to be an open circuit between nodes 1 and 2. Note that it is incorrect to
say that there is then no resistance between nodes 1 and 2 because in fact
there is infinite resistance between them.
9 Branch: a single element or group of elements with two terminals which
form the only connections to other single elements or groups of elements is
called a branch. In the diagrams of Figs 3.1 and 3.2 there are three
branches, one between nodes 6 and 2, one between nodes 2 and 4 and the
other between nodes 5 and 2.
9 Branch current: the current flowing in a branch is called a branch current.
Currents/1, 12 and 13 in the diagrams are branch currents.
9 Mesh: a path through two or more branches which forms a closed path is
called a mesh. There are two meshes in the diagram: one passes through
resistors R1, R4 and the battery V (nodes 1, 2, 5, 6, 1); the other passes
through resistors R2, R3, and R 4 (nodes 2, 3, 4, 5, 2). A mesh is also called a
loop but it cannot have any other loops inside it. The loop containing
resistors R1, R2, R3 and the battery V (nodes 1, 2, 3, 4, 5, 6, 1) is therefore
not a mesh. In other words, a mesh is a loop but a loop is not necessarily a
mesh.
9 Mesh current: the currents Ia and Ib are called mesh currents. Note that the
branch current/1 is the same as the mesh current Ia but that the branch
current 13 is the mesh current Ia minus the mesh current lb.