Paper 2 Semiconductors and Diodes Answers

Q1 Diode I-V Characteristic

1. Reverse current is negligible/approximately zero in the simple model. [1]
2. Once sufficiently forward biased, a small increase in p.d. gives a large increase in current. [2]
3. The I-V graph is non-linear, so $V/I$ is not constant. [2]

Q2 Sensor Potential Divider

1. $V_{out}=6.0(6.0)/(4.0+6.0)=3.6\mathrm{V}$. [2]
2. NTC resistance decreases as temperature increases, so the lower resistor gets a smaller share and $V_{out}$ decreases. [2]
3. The output is the p.d. across a specified component; moving the sensor to the upper or lower part reverses the output trend. [2]

Q3 Half-Wave Rectification

1. The diode conducts during the half-cycle when forward biased and blocks the opposite half-cycle. [2]
2. Current has one direction but its magnitude rises and falls with the input; without smoothing it is not constant. [2]