According to Ohm's law, current through a conductor and the potential difference between it's end are proportional. The constant of proportionality is called the resistance. Mathematically *R* = (*V*)/(*I*). When two resistors are connected in series, the current will be same through both. *I* = (*V*_{1})/(*R*_{1}) = (*V*_{2})/(*R*_{2}). if the value of one resistance and the voltage across both are known, the other resistance can be calculated from
*R*_{1} = *R*_{2} × (*V*_{1})/(*V*_{2})

Find the value of an unknown resistance by comparing it with a known resistance, using the equations given above. Assume R1 is the unknown resistance and R2 is 1000Ω

- Fix the two resisters in series on a bread board.
- Connect the junction to A1
- Connect the other end of R2(1
*k*Ω) to Ground. - Connect one end of R1 to PV1
- Set PV1 to 4 volts.
- Enable the Checkbutton on top right, to measure the DC voltage at A1.

Current *I* = (*V*_{A1})/(*R*_{2}) and R1 can be calculated using
*R*_{1} = (*V*_{PV1} − *V*_{A1})/(*I*).

It can be easily shown that this measurement can be done using AC also. We will use both A1 and A2 inputs here.

- Fix the two resisters in series on a bread board.
- Connect the junction to A2
- Connect the other end of R2(1
*k*Ω) to Ground. - Connect one end of R1 to both WG and A1
- Set WG to 1000Hz
- Enable A1 and A2
- Enable the Cursor Check button to diplay the voltages at the cursor

Taking voltage reading from the picture below,
*I* = (1.92)/(1000) and *R*1 = (3.01 − 1.92)/(0.00192) = 576.7

In this measurements we have made the assumption that no current flows in to A1 and A2. This is not true, they both have an input impedance of 1*M*Ω . This will matter when we use resistance values of mega Ohms range. To illustrate this
connect WG to A1 using a wire and the same signal to A2 through a 1*M*Ω resistor. Try to explain the results using Ohm's law.