# Measure resistance by comparison

Objective

Learn to apply Ohm’s law to find the value of an unknown resistance by comparing it with a known one. Voltage across a resistor is given by V = IR . If same amount of current is flowing through two different resistors, the ratio of voltages will be the same as the ratio of resistances, .

Procedure

- Connect the unknown resistor R from PV1 to A1.

- Connect () from A1 to Ground.

- Set PV1 to 4 volts.

- Measure voltage at A1. Calculate the current . Value of .

- Select Electrical->Plot I-V curve from the menu to get an I-V plot

Discussion

What is the limitation of this method ? How do we choose the reference resistor ? suppose the unknown value is in , what will be the voltage drop across a reference resistor ? Our voltage measurement is having a resolution of .

We will use this method later to measure the resistance of solutions, using AC.