I am learning how to use an oscilloscope and I have just seen this picture in my textbook: enter image description here

I'm not very sure, but I think the arrangement of the probes is incorrect. Isn't the alligator clip connected to the ground already? This will cause a short-circuit and it would damage the oscilloscope, wouldn't it?

Thank you

  • \$\begingroup\$ Depending on the scope, there may not be an earth ground connection on that side of things either. But the ground clips do need to connect to the same node of the circuit (and if there is no ground on the scope side, you need to think about that with some care when choosing where to connect the ground clips.) My main scope has a two-prong plug, or it can take a 24V battery supply. \$\endgroup\$
    – Ecnerwal
    Feb 21, 2016 at 5:29

1 Answer 1


The circuit as drawn has no earth connection so it is isolated from earth. You can, therefore, connect any single point of it to ground without a problem.

Note that the circuit correctly shows both alligator clips connected to the same point in the circuit. If the probe and clip on R2 were swapped then R2 would be shorted out by the earths through the oscilloscope. That could be very bad in a high-powered circuit!

Note also that the probes are measuring voltages away from the common point so the waveforms will be inverted relative to each other. Most 'scopes have an "invert" function on one or both traces to cope with this situation.


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