Two resistances, r1 and r2, are connected in series across a 12-v battery. the current increases by 0.20 a when r2 is removed, leaving r1 connected across the battery. however, the current increases by just 0.13 a when r1 is removed, leaving r2 connected across the battery. find (a) r1 and (b) r2.

Respuesta :

The values of resistance r_1=33.3 ohm and r_2 = 41.7 ohm

The total resistance in series is the sum of the value of the resistances. Applying Ohm's law,

[tex] V=I(r_{1} +r_{2} [/tex] .....(1)

When the resistor r_1 is connected, the current increases by 0.2 A

Apply Ohm's law for the resistance r_1.

[tex] V=(I+0.2)r_{1} [/tex] ......(2)

When the resistor r_2 is connected, the current increases by 0.13 A.

Apply Ohm's law for the resistance r_2.

[tex] V=(I+0.13)r_{2} [/tex] ......(3)

From equations (1) and (2)

[tex] I(r_{1} +r_{2} )=(I+0.2)r_{1}
[/tex]

[tex] \frac{r_1+r_2}{r_1} =\frac{I+0.2}{I} \\ 1+\frac{0.2}{I} =1+\frac{r_2}{r_1} \\ \frac{r_2}{r_1} =\frac{0.2}{I} ......(4) [/tex]

Similarly from equations (1) and (3), it can be seen that

[tex] \frac{r_1+r_2}{r_2} =\frac{I+0.13}{I} \\ \frac{r_1}{r_2} =\frac{0.13}{I} ..... (5) [/tex]

From equations (4) and (5),

I=0.16 A

Substituting in equations (2) and (3)

[tex] r_1 =33.3 Ohm\\ r_2 =41.7 Ohm [/tex]