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##### Top Physics 102 Electricity and Magnetism Educators ##### Andy C.

University of Michigan - Ann Arbor

LB  ##### Jared E.

University of Winnipeg

### Video Transcript

in order to Seoul step, eh? In our city charging circuit, we need to basically get the value of resistance are if the capacitor charges to 90% off its final value, and that also in 15 seconds. So we're going to make use off following equation, which is Q is equipped to cule multiplied by one minus is to minus D upon our C. There's a standard question on disk you zero or Q shoes. The charge at its in issued stewed and this R C means Tao, which is called less time constant in second. So not ask for the question we need to substitute so right here that substitute 90% off cue for Q in about a question. So therefore, what's all this further report these values in the question that is 90% off cue? Is it good to Q into one minus? It is to minus D upon Wow, that is RC. Therefore, 90% missed 90 derided by hundreds, so that becomes 0.9. Q is equal to Keogh into one minus E. Reese to minus t upon our C you're gets cancelled from Bo decides thirties 0.9 is equal to one minus eaters to minus t upon our C. Therefore, it is to minus T upon. Our C is equal to one minus zero point night. Okay, for it is to minus D upon our C becomes 0.1. No, In order to solve this further, we are taking the natural log on board decides. So let's take natural log that is denoted as o n on both the sides for this equation. So once you take natural log, it becomes minus t upon are going to see music will do. Natural logo 0.1 So natural local 0.1 is coming as minus two point to the organ. Therefore minus T is equal to R C multiplied by minus two point to you too. ***, do sign gets cancer from both the sides. Therefore, our is equal to you, dear boy. 2.3 old too multiplied by C that is capacitor. Now let's put the values d becomes 15 seconds a bone to point to you too multiplied by capacity of value which is given as 1 25 micro. So micro means Janis reminding six so therefore begin to find final value off our as 5 to 1 to 8.58 rooms. So what we can right is an answer for the step E is thus, register value has to be 5 to 1 to eight forms. This has to be out. Answer for the step. This is the way we need to solve now, Still be. We need to find average current daily word to the flash. Bold. Right. We need to find average current. Did you work two Flash boat. This is what we need to find. So we'll make use off for an equation to find the inclement with respect to current analysis. Okay, so this is a question that you need to remember. Which is Isaac Ward too? The upon our But since we need to find increment, the dome has to be there. That is one minus. Media's too minus d upon our c. You need to remember this equation now the values voter given us, so let us charge down. These values are is equal to fight to 1 to 8 point five items which are already got we as to 75 work which is given then he is equal to one. Include and his two minus three seconds, which is one millisecond and C is given as 1 25 My girlfriend. Now let's go to the next page since the calculation is bit bigger. Therefore, in order to calculate the value of current will just substitute value, that is, we upon our Valium freeze to 75 world upon our value is 5 to 1 to 8.58 monkey applied by one minus. It is too. It is stupid minus D upon our city. So here the value of he's given us one million. So one in credentials from my industry. I don't. Our value is again 5 to 1 to 8.58 multiplied by capacitor value that is 1 to 5 into tennis to minus six. When you saw this particular fraction, that is to 7500 extra value. We get a value as 5.275 in due. Then there's two minus three multiplied by the bracket offender that we get ISS 1.534 in good and this to minus four. So finally we get it as H 0.1, including this to minus seven and beers so we can write it as zero point each one imprudent is to minus example that is pointed on micro on being current. So finally we can right the answer as does average current delivered. Do the flashbulb will be point each one my crew and beer. This is our final answer for step be

##### Top Physics 102 Electricity and Magnetism Educators ##### Andy C.

University of Michigan - Ann Arbor

LB  ##### Jared E.

University of Winnipeg