Electrical Circuits roblem W3: oomider the electrical circuit shown in Fig. 3. A

Question

Electrical Circuits roblem W3: oomider the electrical circuit shown in Fig. 3. Assume that the capacitor was charged prior to connecting to the eineuit and up t to the switch has remained open. (a) Explain (concisely) why such a circuit would be useful (b) Suppose that at t- to, the switch is closed. Will current flow in this circuit? If so, in what direction (c) Figure 5 shows the magnitude of resistor afunction of ume t 2 to, the voltage v across the ons witr for three such circuits with capacitors of a fixed capacitanee c and r resistances of R1, Ra, and Rs. What is the sign of v on the direction of the current) (d) Continuing part (c): Rank the resistances in order of magnitude. Answer (#3):

Explanation / Answer

a] This is an RC discharging circuit and it can be used to develop a voltage across a load resistance R (for example, a bulb) at any given time to when the switch is closed. This is because the capacitor was initially charged.

b] At t = t, the current is maximum o, the current is maximum and it flows from the positive plate of the capacitor to the negative.

c] Potential difference V is positive in the direction of flow of conventional current I.

d] The voltage across R at any time t is given by:

V = Voe-t/RC

so, greater the value of R for a constant capacitance C, faster the potential difference V will drop across C.

Therefore, R1 > R2 > R3.

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