Voltage drop

[alok1982]

Hi,
I had connected a 10 Mega ohm resistor across the 5Vdc. Another end of resistor is kept open (floating).
When I measured voltage at another point it shows 4.5V.

Why this drop happens?

 

[Triode]

It shouldn't. Did you verify that it's actually 5V before the resistor? Sometimes power adapters can be a bit off, and it's normal for old batteries to be low.

 

[atferrari]

Simple as it seems, show the circuit and the points where you measured that voltage.

 

[ericgibbs]

hi 1982,
From your description it suggests you had connected the meter in series with 10meg resistor.?
The meter has internal resistance, so current will flow through the 10meg and the meters resistance, this current will cause a voltage drop across the 10meg.

eg: assume your meter had a 10meg internal resistance, when connected in series with another 10meg connected to 5V, the meter would read 2.5V.
E