A silicon-based 5.1 V Zener diode requires a minimum operating current I of 5.0 mA to maintain its Zener voltage Vz - AQA - A-Level Physics - Question 4 - 2019 - Paper 8
Question 4
A silicon-based 5.1 V Zener diode requires a minimum operating current I of 5.0 mA to maintain its Zener voltage Vz.
Draw on Figure 11 the general I–V characteristi... show full transcript
Worked Solution & Example Answer:A silicon-based 5.1 V Zener diode requires a minimum operating current I of 5.0 mA to maintain its Zener voltage Vz - AQA - A-Level Physics - Question 4 - 2019 - Paper 8
Step 1
Draw on Figure 11 the general I–V characteristic for this diode.
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Answer
The I–V characteristic curve for the Zener diode should show a sharp breakdown at 5.1 V with a small change in current, indicating its behavior as a voltage reference device. The curve slopes upwards in the forward direction before reaching the Zener voltage.
Step 2
State the function of the Zener diode in this circuit.
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Answer
The Zener diode provides a stable reference voltage of 5.1 V, allowing the operational amplifier to maintain a consistent non-inverting input voltage.
Step 3
Deduce whether a 100 Ω, 0.13 W resistor is suitable for R in Figure 12.
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Using the power formula P=I2R, where I is 5 mA, we find:
\text{Since } 0.0025 ext{ W (or 2.5 mW) is less than 0.13 W, the resistor is suitable.}$$
Step 4
Explain how this affects the light intensity at which W changes.
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If the position of the resistor and Zener diode is swapped, the Zener diode will now be directly connected to the voltage source. This may lead to a higher current flowing through the diode, potentially overheating it and affecting the light intensity at which W changes.
Step 5
Write the Boolean algebra expression for the output Q in terms of W, X and Y based on the logic gates shown in Figure 13.
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The output can be expressed as: Q=(X∧Y)∨W
This describes the logic that Q is true if both X and Y are true or if W is true.
Step 6
State one property that makes the MOSFET suitable for interfacing with logic gates.
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The MOSFET has a high input impedance, minimizing the loading effect on the preceding circuit.
