assignment #024 ˆÆ¦Kˆâ—³¬H튽ÌöéýÏÑ“´òî Physics II 04-10-2006
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21:25:24 Query problem set 3 #'2 1-6. How do we determine the current in the circuit and the voltage across each resistor when we know the voltage across a series combination of two known resistances?
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RESPONSE --> current is voltage / resistance voltage is current * resistance
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21:25:38 ** To get the current calculate I = V / R, where R is the sum of the two resistances. To get the voltage across each resistor calculate V = I * R for each resistor. **
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RESPONSE --> Oh R is resistance of both two resistances.
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21:26:47 How do we determine the current and voltage across each resistor when we know the voltage across a parallel combination of two known resistances?
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RESPONSE --> Voltage is resistance * current. The current A is voltage A/resistance A Current B is voltage B/ resistance B Total current is CurretA + CurrentB
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21:27:01 ** The voltage across both resistors is the same and is equal to the voltage across the combination. The current in each resistor is calculated by I = V / R. The total current is the sum of the two currents. **
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RESPONSE --> Voltage is equal in a parallel combination.
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21:28:58 A series circuit contains a capacitor of known capacitance and a resistor of known resistance. The capacitor was originally uncharged before the source voltage was applied, and is in the process of being charged by the source. If we know the charge on the capacitor, how do we find the current through circuit?
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RESPONSE --> The charge on the capacitor and the charge from the charging device will give us the total voltage. The voltage has reached the same as the capacitor when it is fully charged. I am not sure about this quesiton.
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21:30:59 The voltage across the capacitor is equal to the charge divided by capacitance. The voltage across the capacitor opposes the voltage of the source. Since the voltage drop around the complete circuit must be zero, the voltage across the resistor is the difference between source voltage and the voltage across the capacitor. Dividing the voltage across the resistor by the resistance we obtain the current thru the circuit.
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RESPONSE --> V across capacitor = charge/capacitance (total charge that can be held by capacitor?) The voltage of source is opposite to above voltage. Voltage drop must be zero so voltage across resistor is difference between voltage of source and voltage across capacitor. Okay. Voltage of resistor / resistance = current.
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21:33:54 If we know the capacitance and initial charge on a capacitor in series with a resistor of known resistance then how to we find the approximate time required for the capacitor to discharge 1% of its charge through the circuit?
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RESPONSE --> The charge will tell us voltage. If we know the resistance we can find current by using voltage and resistance. If we divide the charge by 100 and take 1 part that is 1 % of the charge. The time required for the capacitor it discharge 1% could be found by dividing by voltage.
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21:34:07 ** From capacitance and initial charge we find the voltage. From the voltage and the resistance we find the current. We take 1% of the initial charge and divide it by the current to get the approximate time required to discharge 1% of the charge. } This result is a slight underestimate of the time required since as the capacitor discharges the current decreases. **
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RESPONSE --> Dividing by CURRENT, not voltage. Okay.
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