Finding the Null Point with a Galvanometer: Advice Needed

[labview1958]

I have set up an apparatus to find the Null point with a galvanometer. I am unable to find one as the galvanometer always points to the right, no matter what. Help anyone?

 

[Studiot]

If the meter points in the same direction at both ends of the adjustment range you will not find a null so check your wiring. That is the usual reason.

 

[labview1958]

The wirings are correct. Here is the circuit.

http://i1233.photobucket.com/albums/ff387/labview1958/th_Clip2.jpg?t=1299755747

 

[Studiot]

It's very hard to make out your circuit since you only posted the thumbnail.

In the interests of progress I have made some sketches because I think you are connecting the potentiometer or slide wire incorrectly.

There are two ways to connect a pot. As a variable resistor and as a potentiometer.

I have shown the variable resistor connection in Fig5 and I think this is what you are doing incorrectly.

You need the potentiometer connection as in Fig1. Note the slide wire or outer (end) terminals of the pot are connected directly across the battery.
The (variable) output voltage is taken from the third terminal or slider.

You can now compare this voltage with another one as in Fig2. The second voltage can be derived from the same battery or a different one. That is why I have shown the connection dotted.
When the voltages are the same, a centre zero meter connected between them will read zero.
Figs3 and 4 show the conditions for the meter to swing left and right.

go well

 

[labview1958]

Here is my circuit. Still cannot find null point.

http://i1233.photobucket.com/albums/ff387/labview1958/Clip2.jpg

 

[Studiot]

Is L₀ a slide wire and does the arrow mean the slider?

 

[labview1958]

Yes. I manage to get the null point for about 10 minutes. I switch off for about 5 minutes. After that I never ever got back the null point. Can help?

 

[Studiot]

I guess one of your cells is exhausted after 10 minutes.
You are not meant to let the system run for that long.

 

[labview1958]

I checked their voltage. The reading was 1.5V for the dry cell and 6V for the driver cell. I am really lost.