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STEP 3 Capacitors are charged by current flowing in the circuit. So we can expect that changing the amount of current will affect how long the circuit takes to charge the capacitor. Since the current is affected by the total resistance in the circuit, the easiest way to adjust the current is to change the resistance. Remove the 100 resistor at R2 and replace it with a 2k2 resistor, as illustrated in the schematic below. • What effect will this change have on the rate of capacitor charging? Why? • What effect will this change have on the rate of capacitor discharging? Why? R1 R2 5.1 ΚΩ 2 ΚΩ wwww C1 PSB + 5 V B1 100 μF ling SW1 With C1 discharged and the 2kQ2 resistor connected at R2, test the circuit. Note: The capacitor will slowly discharge through B1, but it takes a fairly long time. Discharging the capacitor yourself between tests ensures that each circuit test is done under the same conditions. rive Replace the 2k2 resistor at R2 with a 5k102 resistor and test again. Replace the 5k10 resistor at R2 with a 10k2 resistor and test once more. . When you press and hold the button at SW1, is the number of beeps per minute increased, or decreased, by more resistance at R2? (Hint: If the number of beeps has not decreased, check your circuit and test your components because something is not right.) The rate of audible beeps (the number of beeps you can hear per minute) changed in response to changing the resistance in series with the capacitor/buzzer pair. You should have observed that the number of beeps per minuto docross ngs

Remove the 100 resistor at R2 and replace it with a 2k resistor, as illustrated in the schematic below. . What effect will this change have on the rate of capacitor charging? Why? • What effect will this change have on the rate of capacitor discharging? Why? R1 R2 5.1 ΚΩ 2 ΚΩ wwww C1 PSB 5 V B1 100 μF SW1 With C1 discharged and the 2k2 resistor connected at R2, test the circuit. Note: The capacitor will slowly discharge through B1, but it takes a fairly long time. Discharging the capacitor yourself between tests ensures that each circuit test is done under the same conditions. Replace the 2kQ2 resistor at R2 with a 5k102 resistor and test again. Replace the 5k102 resistor at R2 with a 10k2 resistor and test once more. . When you press and hold the button at SW1, is the number of beeps per minute increased, or decreased, by more resistance at R2? (Hint: If the number of beeps has not decreased, check your circuit and test your components because something is not right.) The rate of audible beeps (the number of beeps you can hear per minute) changed in response to changing the resistance in series with the capacitor/buzzer pair. You should have observed that the number of beeps per minute decreased when resistance was increased. That tells you the rate of beeping is directly proportional to the amount of current through the resistors, since the current is also decreased when resistance is increased. +

STEP 4 Consider how current flows in the circuit during capacitor charging and discharging. Trace the current paths through the circuit (using conventional current). When the potential difference across C1 is very low, almost all of the current is charging the capacitor. While the capacitor is charging, current flows from the high side of the PSB, through the resistors at R1 and R2. Then the current is divided by C1 and B1, before returning to ground through SW1. When the potential difference across C1 increases enough to trigger the buzzer, the capacitor is discharged, sending current through B1 along with the current from the PSB. This allows for enough current that the buzzer will emit a beep. Once the buzzer is triggered, its resistance temporarily decreases. The capacitor discharges very quickly, allowing only enough time for a very short beep. This describes the "relaxation" phase of this circuit. The capacitor is charged until it reaches the trigger voltage of the buzzer. Then the capacitor releases its stored energy in a burst of current, "relaxing" to an uncharged state with no potential difference across the capacitor. 3 The capacitor alternates between states of charging and discharging in this circuit. This is defined as a simple type of "oscillating" circuit. The oscillation is a repeating back-and-forth pattern of current flow to and from the capacitor. • Does the buzzer emit a beep while the capacitor is being charged, or while it is being discharged? e • What reasoning supports your answer? STEP 5 Finally, to automate this circuit, replace the 10k2 resistor at R2 with the light-dependent resistor (LDR) from your lab kit and replace SW1 with a jumper wire. The final circuit should match this schematic: R1 ✓✓