1. EXERCISE 3
1. Explain what has contributed to the uptake of interest in solar cells?
2. Primary objective of optical fiber communication system is to transfer the signal
containing information (voice, data, and video) from the source to the destination.
i. Give the definition of fiber optiC
ii. Identify THREE (3) advantages using fiber optics
3. Photodiode can operate in photovoltaic mode of operation.
i. Describe the photovoltaic mode of operation in photodiode
ii. A solar cell is a device that converts the energy of sunlight directly into electricity
by the photovoltaic effect. Clarify the effect of connecting solar cell in parallel or
series.
4. Explain how do solar cells work?
5. There are two element consisting in optocoupler or optoisolator which is light emitter
and light detector.
i. Explain the function of both elements.
ii. What is the difference between optocoupler and optoisolator

2. 6. Light Depending Resistor (LDR) is types of photoconductive cell.
i. Explain the operation based on the resistance-illumination characteristic graph in
Figure 1
Figure 1
ii. Identify TWO (2) application of LDR based on the operating principle
7. Explain what does the term infrared mean?
8. There are several types of solenoid valve that may use in industries
i. Determine the type of solenoid valve as shown in Figure 2
Figure 2
ii. State the application of solenoid valve in Figure 2

3. 9. Three basic types of stepper motors include the permanent magnet motor, the variable
reluctance motor, and the hybrid motor.
i. Describe the advantages of variable reluctance motor
ii. What is the meaning of “step angle” in stepper motor
10. Explain are infrared rays easy to focus?
11. A DC servomotor has a torque constant Kt= 0.095 N-m/A. Its voltage constant Kv= 0.11
V/(rad/sec). The armature resistance is Ra = 1.6 ohms. A terminal voltage of 24V is used
to operate the motor.
Calculate:
i. starting torque generated by the motor.
ii. maximum speed at a torque of zero
12. Explain what happens if you feed an optical node with a too high level of light?
13. An Electrical motor uses electrical energy to produce mechanical energy.
i. State TWO (2) major component of AC motor
ii. What is the difference of the build construction in both types of AC motor
14. There are many factors need to be consider before choose the appropriate motor
specification.
Describe THREE (3) selection criteria of a motor
15. A 4-pole induction motor is built to operate on 50 Hertz.
i. Calculate the synchronous speed of the motor
ii What is the effect of increasing the number of poles in induction motor.
16. The soft starter controls the voltage without steps from a selectable starting value up
to 100 %.

4. Draw the three-phase half-wave controlled soft starter circuit connection
for controlling motor.
17. Figure 4 show the main structure for frequency inverter which is consists of rectifier,
intermediate circuit and inverter. Explain the function of each component in the system
Figure 4
18. List what are the advantages of using fiber optic cables?
19. Compare if fiber optic cables safer than other types of wires?
20. Discuss what is the ability of phototransistor?