Electronics notation - what does R1//R2 mean?

Well, the question is in the title really. Never come across “//” before. Can’t seem to find a google search that will pull it up, probably because of the ubiquity of “//”.

For context, see here

In parallel.

The circuit is fed from a set of voltage sources - so the impedance of the sources is zero. Thus the resistors all appear in parallel for the purposes of calculating the gain etc.

It means r1 in parallel with r2.

It’s shorthand for 1/(1/r1 + 1/r2).

Huh, thanks guys. That’s what I thought it should be, but then everywhere I tried to look it up suggested that parallel was “||” not “//” so I thought it had to be something different.

Both are used, but I think // is common in engineering because || looks too much like 11.