Paper 3 Semiconductors and Diodes Drills

Q1 Sensor Circuit Design

A warning circuit should give a larger output p.d. when light intensity increases. An LDR and a fixed resistor are connected as a potential divider to a $9.0\mathrm{V}$ supply.

1. State whether the LDR should be the upper or lower resistor if output is measured across the lower component. [2]
2. When the LDR is $12\mathrm{k\Omega }$ and the fixed resistor is $6.0\mathrm{k\Omega }$, calculate output if the fixed resistor is lower. [2]
3. Explain the output trend as light intensity increases. [3]

Q2 Semiconductor Control

1. Explain qualitatively why thermistor resistance decreases when temperature rises. [2]
2. Explain qualitatively why LDR resistance decreases in brighter light. [2]
3. Compare sensor use with diode rectifier use. [3]