What Causes the Amplitude Increase on an Oscilloscope When Touching the Lead?

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SUMMARY

The amplitude increase observed on an oscilloscope when touching the lead is primarily due to the human body acting as an antenna for electromagnetic signals, typically at frequencies of 50 Hz or 60 Hz from nearby electrical outlets. When the input lead is touched, these ambient signals are coupled into the oscilloscope, resulting in a larger displayed wave. Understanding this phenomenon requires a grasp of how oscilloscopes detect voltage and represent it as a function of time, as well as the principles of electromagnetic interference.

PREREQUISITES
  • Basic understanding of oscilloscopes and their function in voltage detection
  • Familiarity with electromagnetic signals and their sources
  • Knowledge of signal coupling and interference concepts
  • Awareness of frequency standards (50 Hz and 60 Hz) in electrical systems
NEXT STEPS
  • Research the principles of electromagnetic interference and its effects on electronic measurements
  • Learn about oscilloscope operation, including voltage detection and signal representation
  • Explore the concept of signal coupling and how it affects measurements in oscilloscopes
  • Investigate the role of the human body as an antenna in electronic environments
USEFUL FOR

Electronics students, hobbyists working with oscilloscopes, and professionals in fields requiring signal analysis will benefit from this discussion.

nietzsche
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Hi PF, it's been a long time since I've posted on here. I have a lab due soon and it was regarding oscilloscopes. This isn't really a homework problem so I'm not using the template...

Anyways, when I held the input lead in my hand, the amplitude of the wave displayed on the screen got much larger. I can't think of a reason why that would be. TBH, I still don't fully understand the concept of the oscilloscope. I understand that it detects voltage and graphs it as a function of time. But where is this mysterious voltage coming from when I touch the lead? And why is it even a wave?

Thanks in advance for your help.
 
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You are surrounded by electromagnetic signals (at either 50 Hz or 60 Hz), due to the electricity powering the outlets in the room you are in.

Your body acts like an antenna for these signals. By touching the oscilloscope lead, this signal is displayed on the oscilloscope.
 
Thanks Redbelly. I suspected it had to do with some antenna affect. It's still confusing though... it's so hard for me to understand things when they're invisible.
 

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