Worksheet Chapter 5: Electronics

1. A transistor amplifier circuit operates with a base current I_B of 40 µA and a collector current I_C of 3.6 mA. (a) Calculate the emitter current I_E in mA. (b) Calculate the current amplification factor (β) of the transistor.

2. Fill in the blank: The process of adding tiny amounts of impurity atoms to a pure intrinsic semiconductor to enhance its electrical conductivity is called ________.

3. True or False: A semiconductor diode conducts current when its p-type region is connected to the negative terminal of a battery and its n-type region to the positive terminal.

4. An automatic fire alarm switching circuit uses an npn transistor, a fixed resistor R1 = 1 kΩ, a thermistor R_T, and a 6 V power source. The transistor turns ON when base voltage V_BE ≥ 0.8 V. (a) Should the thermistor be placed at the upper or lower position of the potential divider relative to the base to turn ON the alarm during a fire? Explain. (b) If R_T drops to 200 Ω at high temperature and is placed at the lower position, calculate V_BE.

5. True or False: In an npn transistor, the majority charge carriers inside the emitter and collector regions are holes.

6. In an electron gun of a Cathode Ray Tube, electrons are accelerated from rest across an anode voltage of 3.2 kV. (a) State the energy transformation taking place. (b) Calculate the maximum kinetic energy gained by an electron. (c) Calculate the maximum velocity reached by the electrons.

7. A semiconductor diode is connected to a 6 V a.c. supply and a load resistor in a half-wave rectifier circuit. (a) Sketch/describe the output voltage waveform across the load resistor without a capacitor. (b) Explain how adding a capacitor in parallel across the load resistor alters the output waveform.

8. A Cathode Ray Oscilloscope (CRO) is connected to an a.c. voltage signal. The Y-gain is set to 2 V/div and the Time-Base is set to 5 ms/div. The trace on the screen shows a peak-to-peak height of 6 divisions and 1 complete wave cycle occupies 4 horizontal divisions. (a) Calculate the peak voltage (V_p) of the a.c. signal. (b) Calculate the period (T) of the a.c. signal. (c) Calculate the frequency (f) of the a.c. signal.

9. Explain the working principle of a transistor used as an automatic light-controlled switch for street lamps using an LDR and potential divider circuit. (a) Describe how LDR resistance changes in dark conditions. (b) Explain how this change in resistance turns on the street lamp connected to the collector circuit.

10. Which combination of components is required to construct a full-wave smoothed direct current (d.c.) power supply from an alternating current (a.c.) source?