Question

A circuit consists of two resistors with resistances R, = 6.0O 2 and R, = 1.5 2., a variable resistor, the resistance R of which can be adjusted, a resistor of unknown value R. and 9.0 volt battery connected as shown in the figure. When R is adjusted to current through the ammeter. What is the unknown resistance

Answer 1

What we have here is a Wheatstone bridge. The unknown resistance is

$$R_x=\frac{R_V}{R_1}R_2=\frac{R_V}{6}·1.5=\frac{R_V}{4},$$

where $R_V$ is the variable resistance.