fA
femtoampere
Electric currentexact by definition
The femtoampere is 10⁻¹⁵ of an ampere, about 6240 electrons per second. It is the working floor of electrometers and picoammeters, used for ionisation chamber currents, photomultiplier dark current and gate leakage in low-power semiconductor test. The factor is exact, being an SI prefix.
Watch out: At femtoamperes the measurement is a battle against the fixture rather than the instrument. Surface leakage across a fingerprint on an insulator, triboelectric charge from a flexed cable and piezoelectric current from a stressed dielectric all exceed the signal, which is why guarded triaxial cable and a driven guard ring are standard practice.
| 1 fA | 1.0000000e-15 A |
Solvers that use electric current