QUESTIONS 1. Why? Equations (1) and (2) are true? 2. Why should the wires connec

Question

QUESTIONS 1. Why? Equations (1) and (2) are true? 2. Why should the wires connecting the resistances and the Wheatstone bridge be as short as possible? Explain. Why is does one need to turn off the circuit in-between measurement when using the Wheatstone 3. 4. If the power supply was connected in reverse, where the positive terminal is connected to d instead of a, 5. bridge? Explain. will the outcome be different? Explain. Suppose the slide wire on the bridge does not have a uniform cross sectional area. How would this affect your measurement? 6. Why is the Wheatstone Bridge called a "null" instrument? 7. When the galvanometer in a Wheatstone bridge circuit shows no deflection, why are the voltages across opposite branches on each side of the galvanometer necessarily equal?

Explanation / Answer

Answer 1

Potential difference between points d and c that is Vdc and potential difference b and c that is V bc are equal according to equation 1 is correct because when galvanometer shows null deflection means no current in the branch connected between points d and b. that means potential of point d with respect to c as well as potential of point b with respect to c must be equal. Because current flows from high potential to low potential, but if no current flowing through galvanometer means no potential difference between those points.

Similarly with points b and d and points b and a as there is no current through Galvanometer. hence Vbd = Vba. So the eqation (1) and (2) are correct

Answer 2

While measuring low resistances with the help of wheatstone bridge experiment , the resistances of connecting wires become comparable to the unknown low resistance and hence they can not be neglected then. So if the connecting wires are kept short length then their resistance can be neglewcted in calculation of unknown resistance with this experiment.

Answer 3

while measurement if we turn off circuit beteewn few measurements it is good because if we keep the circuit on full time then since due to flow of current heating effect takes place. The resistance of wires and resistances effect due to the change in temperature. As well as if the circuit is kept on long time then battery get discharged soon and it appears that we got the null point but in the case battery is not giving current, so it creates confussion.

Answer 4

If the power supply is connected reverse it will not affect the outcome. Readings in the experiment will be different but once the wheatstone get balance ratio will not change and hence outcome will not change.

Answer 5

If slide wire does not have uniform cross sectional area then resistance of the slide wire is not uniform and hence we will have to calculate the resistance of two sections that length L and 100 - L separately, when we get the null points, We will have to make a function for resistance of the slide wire with respect to lewngth and area.

So it will affect our m,easurement, it will increase the calculation as well and length of null point as well, but the value of unknown resistance will be same, so outcome will be same.

Answer 6

It is called null instrument because we obtain Null point in one diagonal in which galvanometer is connceted, then only bridge is balance and hence ratio of adjecent branch resistances become equal.

Answer 7

Voltage across opposite branches of gal;avanometer is equal because no current flows through a branch when two points are at the same potentials. Otherwise if two opposite end points of the branch are at different potentials then there will be a flow of current from high potential to low potential and then galvanometer connected in that branch can not show null deflection.

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