| (a) | It acts as a voltage regulator. |
| (b) | It is used in forward bias. |
| (c) | It is used in reverse bias. |
| (d) | It is used as a switch in series. |
| 1. | (a) and (d) |
| 2. | (b) and (c) |
| 3. | (a) and (c) |
| 4. | (b) and (d) |
The advantages of LEDs are:
| 1. | long lifespan |
| 2. | quick on-off switching |
| 3. | low operating voltage |
| 4. | all of the above |
If a semiconductor photodiode can detect a photon with a maximum wavelength of \(400~\text{nm},\) then the energy of its band gap is:
(take Planck’s constant \(h=6.63 \times 10^{-34} \text { J-s }\) and speed of light \(c=3 \times 10^8\) m/s)
1. \(3.1~\text{eV}\)
2. \(1.1~\text{eV}\)
3. \(2.0~\text{eV}\)
4. \(1.5~\text{eV}\)

| 1. | a \(\mathrm{p}\)-doped silicon that emits light |
| 2. | a \(\mathrm{n}\)-doped silicon that emits light |
| 3. | a \(\mathrm{p \text-n}\) diode that emits light |
| 4. | a transistor that absorbs light |
| 1. | open circuit voltage; short circuit current |
| 2. | open circuit voltage; open circuit current |
| 3. | short circuit voltage; short circuit current |
| 4. | short circuit voltage; open circuit current |