On non linear resistor and how to calculate a fixed resistor.

[physikamateur]

Homework Statement

The current in amperes through a certain type of non-linear resistor is given by I=0.05V^3, where V is the potential difference in volts across the resistor. This resistor is connected in series to a fixed resistor and a constant voltage source of 9V is connected across the series combination. What value of resistance should the fixed resistor have so that a current of 0.40A flows ?

Homework Equations

V=IR and P=VI ?

The Attempt at a Solution

I first tried to calculate the total resistance which gives 22.5 ohms. But I do not know how to calculate the non-linear resistor as it does not obey ohm's law hence no proper formula can be used ? Please help.

Thank you.

 

[gneill]

Suppose that, as stated, a current of 0.40A is flowing through the nonlinear resistor. What will be the voltage drop across it according to the given formula for it (you may have to rearrange the formula)?

 

[physikamateur]

By I=0.05V^3, when I=0.40A, V=2V. Hence voltage drop across the fixed resistor is 9-2=7V.
Therefore by V=IR, 7=0.4R,
Therefore R=17.5 ohms

Am I right ?

 

[gneill]

Looks good!

 

[physikamateur]

Thanks a lot !