21.5 Null measurements  (Page 3/8)

Identify other factors that might limit the accuracy of null measurements. Would the use of a digital device that is more sensitive than a galvanometer improve the accuracy of null measurements?

Why can a null measurement be more accurate than one using standard voltmeters and ammeters? What factors limit the accuracy of null measurements?

If a potentiometer is used to measure cell emfs on the order of a few volts, why is it most accurate for the standard ${\text{emf}}_{\text{s}}$ to be the same order of magnitude and the resistances to be in the range of a few ohms?

What is the ${\text{emf}}_{\text{x}}$ of a cell being measured in a potentiometer, if the standard cell’s emf is 12.0 V and the potentiometer balances for $R_{\text{x}}=5\text{.}\text{000}\Omega$ and $R_{\text{s}}=2\text{.}\text{500}\Omega$ ?

Calculate the ${\text{emf}}_{\text{x}}$ of a dry cell for which a potentiometer is balanced when $R_{\text{x}}=1\text{.}\text{200}\Omega$ , while an alkaline standard cell with an emf of 1.600 V requires $R_{\text{s}}=1\text{.}\text{247}\Omega$ to balance the potentiometer.

When an unknown resistance $R_{\text{x}}$ is placed in a Wheatstone bridge, it is possible to balance the bridge by adjusting $R_3$ to be $\text{2500}\Omega$ . What is $R_{\text{x}}$ if $\frac{R_2}{R_1}=0\text{.}\text{625}$ ?

To what value must you adjust $R_3$ to balance a Wheatstone bridge, if the unknown resistance $R_{\text{x}}$ is $\text{100}\Omega$ , $R_1$ is $\text{50}\text{.}0\Omega$ , and $R_2$ is $\text{175}\Omega$ ?

(a) What is the unknown ${\text{emf}}_{\text{x}}$ in a potentiometer that balances when $R_{\text{x}}$ is $\text{10}\text{.}0\Omega$ , and balances when $R_{\text{s}}$ is $\text{15}\text{.}0\Omega$ for a standard 3.000-V emf? (b) The same ${\text{emf}}_{\text{x}}$ is placed in the same potentiometer, which now balances when $R_{\text{s}}$ is $\text{15}\text{.}0\Omega$ for a standard emf of 3.100 V. At what resistance $R_{\text{x}}$ will the potentiometer balance?

Suppose you want to measure resistances in the range from $\text{10}\text{.}0\Omega$ to $\text{10}\text{.}\mathrm{0\; k\Omega }$ using a Wheatstone bridge that has $\frac{R_2}{R_1}=2\text{.}\text{000}$ . Over what range should $R_3$ be adjustable?