To solve these questions, we need to analyze the light-activated switch circuit in Figure C3.1 and understand how the Light-Dependent Resistor (LDR), potentiometer $P1$, op-amp, transistor, and diode function within this setup. Here's the approach for each part of the question:

Part (a)

1. Finding the luminosity level where the switch changes state:

   • The potentiometer $P1$ is set at $20 \text{k}\Omega$.
   • From the op-amp configuration in Figure C3.1, this is likely a comparator circuit. The op-amp will compare the voltage at its non-inverting terminal (+) to that at its inverting terminal (-).
   • The inverting input has a reference voltage created by $P1$ and $R1$ (forming a voltage divider with $R2$). We will set up equations based on this voltage divider.

2. LDR Resistance and Luminosity:

   • The LDR’s resistance changes with light intensity (lux) as shown in Figure C3.2.
   • For an LDR resistance $R_{LDR}$, at different lux values (like 1k, 2k, etc.), use the graph to find the approximate LDR resistance at each level.
   • Calculate the voltage across the LDR to determine at what lux level the op-amp output changes.

Part (b)

1. Transistor’s Base Voltage at 5kLux and $P1 = 14 \text{k}\Omega$:

   • First, use the LDR curve in Figure C3.2 to determine the resistance of the LDR at 5kLux.
   • With $P1$ set to $14 \text{k}\Omega$, calculate the voltage divider between $R1$, $P1$, and $R2$.
   • Calculate the op-amp’s output based on the input voltage comparison.

2. Diode Conduction Conditions:

   • Analyze when the diode $D1$ conducts (likely when the op-amp’s output is high).
   • Explain its purpose, which might be to protect or control current flow in certain conditions.

Would you like further step-by-step calculations and explanations for each part?

Follow-Up Questions

1. How would changing the potentiometer $P1$ setting affect the switching threshold?
2. What happens if the LDR value is below the calculated threshold luminosity?
3. How does the transistor configuration affect the relay switch activation?
4. What role does the op-amp’s supply voltage play in the circuit's overall function?
5. How would you modify the circuit to make it less sensitive to light changes?

Tip

When working with LDR circuits, remember that LDR resistance decreases as luminosity increases. This behavior can help in setting thresholds for light-activated switches.