Niha afzal Posted March 27, 2016 Share Posted March 27, 2016 Hey guys im back with straight pictures this time .... so happpy :D .... anyways this question I tried the same old Q=IT... but this seems like a trick question. The question at the bottom of the page Link to comment Share on other sites More sharing options...
studiot Posted March 27, 2016 Share Posted March 27, 2016 Since I'm sure you haven't covered differential equations here is another way. Have you done motion under constant acceleration yet? Link to comment Share on other sites More sharing options...
Niha afzal Posted March 27, 2016 Author Share Posted March 27, 2016 Yes the kinematics equation stuff Link to comment Share on other sites More sharing options...
studiot Posted March 27, 2016 Share Posted March 27, 2016 (edited) Look at the following correspondences. When all the rates of change are uniform. velocity is rate of change of distance : current is rate of change of charge So distance ( symbol s) corresponds to charge (symbol q) acceleration is rate of change of velocity : I will call rate of change of current p The kinematics equation s = ut + 0.5 (f t2) Where s is distance, u is initial velocity, t is time and f i acceleration. This equation also applies to your uniform change of current. i = initial current = 100mA the current changes from 100mA to 20 mA in 8 seconds ie (20 - 100) /8 = -10 mA per second. So p = 10 mA/s2 Changing our formula from s = ut + 0.5 (f t2) to q = it + 0.5 (pt2) = 8 q = 100 * 8 + (-10 *64) millicoulombs which I think you will find is answer A Edit q = 100 * 8 + 0.5(-10 *64) millicoulombs which I think you will find is answer C Edited March 27, 2016 by studiot Link to comment Share on other sites More sharing options...
Niha afzal Posted March 27, 2016 Author Share Posted March 27, 2016 Beautiful beautiful beautiful. ... I see what you are saying ... I calculated it its 480 I.e C Thanks Link to comment Share on other sites More sharing options...
studiot Posted March 27, 2016 Share Posted March 27, 2016 (edited) Good to see you checked my arithmetic, and found the missing 0.5. Students should always do this. Incidentally what are you studying Physics or Engineering Science? I chose this method because I don't know if you have any calculus, which would be the standard method. Edited March 27, 2016 by studiot Link to comment Share on other sites More sharing options...
Niha afzal Posted March 27, 2016 Author Share Posted March 27, 2016 I did basic calculus .... im still doing my alevels ...therefore I have both physics and maths .. but basic math This kinematics working was amazing.. who knew we could relate kinematics and elctricity like this.... this was amazing seriously yet im scared how will I figure out stuff like this. My best bet is practising a loooot! I find no words to thank you :') Link to comment Share on other sites More sharing options...
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