# IMPORTANT DOUBT

Discussion in 'General Electronics Chat' started by whale, Jan 29, 2009.

1. ### whale Thread Starter Active Member

Dec 21, 2008
111
0
I CONNECTED +VE OF DC SOURCE(15V) TO A RESISTOR(100KΩ),WHEN I MEASURED POTENTIAL ACROSS -VE OF SOURCE AND ANOTHER END OF RESISTOR I COULD MEASURE ABOUT 13V,EVEN WHEN I MADE MY BODY AS RESISTOR I COULD GET 12V.
HOW CAN THIS HAPPEN?
WHEN WE CONSIDER -VE TERMINAL AT GROUND POTENTIAL,THEN +VE TERMINAL IS +15V(IT ACCEPTS ELECTRON AT A POTENTIAL 15V).

BUT WHEN THIS +VE TERMINAL IS CONNECTED TO HIGH RESISTANCE ,THE POTENTIAL BETWEEN RESISTOR ANOTHER END AND -VE OF SOURCE SHOULD REDUCE A LOT .BECAUSE IT ALLOWS ONLY FEW ELECTRONS TO PASS THROUGH.THUS THE DIFFERENCE IN ELECTRON LEVEL DECREASES THUS POTENTIAL SHOULD REDUCE.

WHY IT DONT HAPPEN?

2. ### Wendy Moderator

Mar 24, 2008
20,772
2,540
100KΩ isn't that large. Try 10MΩ instead.

3. ### ifixit Distinguished Member

Nov 20, 2008
639
110
The input impedance of the voltmeter will effect your reading. Ohms law: E=I x R.

4. ### whale Thread Starter Active Member

Dec 21, 2008
111
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ofcourse i too tryed with my body(2 mega ohm ),the same thing happen

5. ### whale Thread Starter Active Member

Dec 21, 2008
111
0
iam waiting for answers, do it fast...............

6. ### SgtWookie Expert

Jul 17, 2007
22,183
1,728
It appears that your 15v source has a rather high internal impedance.
When you connect an external resistance across it's +V and -V terminals, you wind up with a voltage divider; some of the voltage is dropped across the internal resistance, and the rest is dropped across the external resistance.

7. ### whale Thread Starter Active Member

Dec 21, 2008
111
0
the source give 0.5A at short circuit.my question is how the electrons are accumulated the terminal of 10k ohm resistor,whose another terminal is connected to -ve of source.
with respect to +ve of source.
i can clearly identify that no current flow takes place. but how a 15v(between +ve and -ve)potential diff remains with less distrotation about 12v(between +ve and terminal of resistor,whose another terminal is connected to -ve of source)

8. ### SgtWookie Expert

Jul 17, 2007
22,183
1,728
You are not making sense.

If you connect a resistance across a voltage source, there will be a flow of current.
I = E/R, or Current(Amperes) = Voltage/Resistance(Ohms).
Therefore, if you place a 10k Ohm resistor across a 15v source (an ideal voltage source that has an impedance of zero Ohms), you will have 1.5mA (0.0015 Amperes) current flow through the resistor.