A charging RC circuit controls the intermittent windshield wipers in a car. The emf is 12.0V. The wipers are triggered when the voltage across the 125(micro)F capacitor reaches 10.0V; then the capacitor is quickly discharged (through a much smaller resistor) and the cycle repeats. What resistance should be used in the charging circuit if the wipers are to operate once every 1.80s?
2007-02-22 08:57:16 · 3 answers · asked by Sir Guitarist 2 in Science & Mathematics ➔ Engineering
nope.
v(t) = Vo(1 - e^(-T/t)
10V = 12V(1 - e^(-1.8s/R*125uF)
10V/12V = 1 - e^(-1.8s/R*125uF)
-1 + 10V/12V = -e^(-1.8s/R*125uF)
-0.1667 = -e^(-1.8s/R*125uF)
0.1667 = e^(-1.8s/R*125uF)
ln(0.1667) = -1.8s/R*125uF
R = -1.8s/(ln(0.1667)*125uF)
R = 8037.69 ohms or 8K ohms
2007-02-23 04:36:39 · answer #1 · answered by joshnya68 4 · 0⤊ 0⤋
OK. The voltage across the capacitor is given by
v = V(1 - e^(t/RC)) so
ln(v/V) = -t/RC and
R = -t/Cln(v/V) = -1.8/((125*10^(-6))*ln(10/12)) = 78981 ohms
HTH âº
Doug
2007-02-22 11:37:59 · answer #2 · answered by doug_donaghue 7 · 0⤊ 0⤋
Are you trying to get the answer to a circuits homework problem?
2007-02-22 09:42:42 · answer #3 · answered by Chris P 1 · 0⤊ 0⤋