1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: How do I calculate di/dt?

  1. Aug 13, 2011 #1
    1. The problem statement, all variables and given/known data

    A circuit has a 10v battery, an 1 henry inductor, and a switch connected in series. The circuit's total resistance is 10k ohms. If the inductors maximum current is 1mA and the switch is suddenly opened how do I calculate di/dt?

    Wouldn't the open switch be an infinite impedance and produce infinite voltage across the inductor?

    2. Relevant equations

    V=L x di/dt

    3. The attempt at a solution

    Not sure where to even start?
  2. jcsd
  3. Aug 13, 2011 #2
    first consider the switch is closed and current is flowing at steady rate(think about it, why it should flow at a steady rate? if u don't know it already), the value is given as 1mA. u can also calculate it from given data (how?), had it not given.
    now consider the switch is suddenly open. the physical consideration should be, the applied voltage is zero (and not the resistance is infinity. why?).
    now set up the ckt eqn. considering potential drops across the inductor and the resistor and applied voltage zero. solve the differential eqn (u will need the value i initial = 1 mA here). and find i as a function of t. put the given values for inductor and resistor and find di/dt by differentiation.
  4. Aug 13, 2011 #3


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Education Advisor

    Can you provide a drawing of the circuit? The problem seems a bit strange for an intro physics class.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook