# need help in electric

Discussion in 'Homework Help' started by haider_alkaisy, Jan 24, 2011.

1. ### haider_alkaisy Thread Starter New Member

Jan 14, 2011
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0
hi guys

i need help i have a question in electric the question said :

why we have get a diffrence in the value that sourced by power supply when we measure it by multimeter in the practical experience of the value that we get it theoretically ?

thank you very much and i hope all help me in this question

2. ### thatoneguy AAC Fanatic!

Feb 19, 2009
6,357
718
When a load is placed on a battery or not-fully regulated supply, the voltage goes down due to the internal resistance of the source.

I'm not sure if that is what you are asking or not.

The other answer would be tolerances and parasitic resistance/inductance/capacitance.

3. ### haider_alkaisy Thread Starter New Member

Jan 14, 2011
4
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thank you for response and i am sorry for not clarifying whether the resistance or /inductance/capacitance but i replay my question :why we have get a diffrence in the value that sourced by power supply that provide a voltage when we measured it in a rsesistor by multimeter in the practical experience of the value that we get it theoretically for example we have a source provided 10 volt and we have three resistors when measure this three resistors by multimeter and collect the voltage in the three resistors the resultant for the three resistors does not equal 10 volt we get 9.96 volt ?

4. ### Kermit2 AAC Fanatic!

Feb 5, 2010
3,847
963
The supply measures 10.00 volts, or 9.96 volts?

use the meter to measure the supply from top of 1st resistor to bottom of 3rd resistor....it should equal the total of the readings, or be much closer, say 9.97 volts.

measure the supply without any resistors connected and again with the resistors connected....is there any difference in the two readings?

5. ### haider_alkaisy Thread Starter New Member

Jan 14, 2011
4
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thank you for response the supply read 10 volt but when we calculate the resultant for the three resistors we get 9.96 in practical experience but when we calculate the resultant in the three resistors theoretically we get 10 volts so we get a percent error that equal 0.56 %

6. ### thatoneguy AAC Fanatic!

Feb 19, 2009
6,357
718
What brand meter are you using? Is it a Digital Multimeter or VOM (Analog/needle)?

Are you measuring the source with the load connected, e.g. measuring 10V, then plugging in resistors and measuring them? The voltage drop across all 3 resistors would be the supply voltage, and if you add the drops, you shouldn't have any error.

7. ### haider_alkaisy Thread Starter New Member

Jan 14, 2011
4
0
Are you measuring the source with the load connected ? the 10 volts before the source connected and the 9.96 volts after the source connected

Is it a Digital Multimeter or VOM (Analog/needle)? yes it is Digital Multimeter

8. ### thatoneguy AAC Fanatic!

Feb 19, 2009
6,357
718
Your source voltage is going down when the resistors are connected.

If you measure the source with the load (resistors), the drops across the resistors will add up fine.