The frequency meter in the quantum mechanics lab is likely detecting the mains frequency, which is typically around 50 Hz, even when the device is off. This phenomenon is common in frequency detection devices, as they often include narrowband band-stop filters for 50 Hz and 100 Hz to mitigate interference. Such readings are not indicative of a problem but rather a normal effect of electrical noise. Understanding this can help clarify the source of the readings. Proper calibration and awareness of environmental factors are essential in experimental setups.
