Use the following circuit diagram from Lab 4. The PS supplies 5V and the R and C

Question

Use the following circuit diagram from Lab 4. The PS supplies 5V and the R and C are chosen to be 5k ohm and 1000 mu F respectively. The positive lead of the ammeter is connected to the switch, while the negative lead is connected to the resistor. When the switch is in position 1, would the ammeter measure a positive or a negative current? How would that current change over time? To what maximum voltage will the capacitor charge? If the 5k ohm resistor is swapped with a 10k ohm resistor and the capacitor is replaced by a 3000 mu F version, what is the maximum voltage the new capacitor will charge to? Did replacing the resistor and capacitor in Question 2 increase or decrease the time it took to reach its maximum value? You are given the circuit in Figure 1 (R is 5k ohm and C is 1000 mu F) along with 10 extra 5k ohm resistors and 10 extra 1000 mu F capacitors. Draw a modified circuit diagram with the following three properties: Capacitance is tripled. 2: RC time to charge is unchanged. 3: RC time to discharge is tripled.

Explanation / Answer

Question 1:

Yes the ammeter will measure a positive current . the magnitude of the current will decrease expontially with time . since this is an RC circuit and in RC circuit , current at any time "t" is given as

I = Io e-t/T            where Io = maximum current and T = time constant

Question 2 :

The capacitor will get charged until the voltage across it becomes equal to the voltage of the battery.

Vc = Maximum Voltage across capacitor = battery Voltage = V = 5 volts

changing the capacitor value or the resistance value does not change the voltage to which the capacitor gets charged to when connected to a 5 volts battery. the capacitor will still have maximum voltage as 5 Volts

Question 3 :

Time constant is given as T = RC

replacing R and C with new larger values will increase the time constant and hence the time for the capacitor to get fully charged will increase too

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