QUESTION 1 1.1 Explain the principle of operation of a heater that falls into the radiant category. 1.2 Name TWO other categories for space heaters, apart from the one mentioned in QUESTION 1.1. 1.3 The TwO motors in a twin tub washing machine operate at different speeds. Refer to the construction of the motors to indicate the speed difference. 1.4 Name TWO electrical protection devices that are commonly used in stove wiring QUESTION 2 2.1 Name the correct rating for circuil breakers used in the following subcircuits. 211 Light subcircult 2.1.2 Slove subcircuit 2.1.3 Geyser subcircuit \( (3 \times 1) \) 22 Explain the operating principle of an immersion thermostat commonly found in geysers. 2.3 Draw the wiring diagram of a geyser subcircuit QUESTION 3 31 Use the sketch in FIGURE 1 below to explain the operation of the sodium vapour lamp 11038

Below is one acceptable set of answers. Note that wording may vary, but the following covers key points: ────────────────────────────── QUESTION 1 1.1 Radiant Heater – Principle of Operation A radiant heater works by converting electrical energy into heat via a high‐resistance element. When current flows through this element it becomes hot and mainly emits infrared radiation. Rather than heating the air (as in convection heaters), the infrared (or radiant) energy is directed toward objects and people, which absorb the radiant heat and warm up. The design is similar to that of an incandescent lamp (though usually with a purpose‐designed element and reflector) so that the heat is “radiated” outward directly. 1.2 Two Other Categories for Space Heaters Apart from radiant heaters, two other common types are: • Convection heaters – These warm the air in a room by heating it and letting it circulate naturally (or with a fan assistance). • Fan heaters (or forced-air heaters) – These use an electrical resistive element to heat air that is actively blown by a fan into the room. 1.3 Explaining Different Speeds in Twin Tub Washing Machine Motors For motors the running speed is largely determined by the number of magnetic poles (in AC machines) or the construction details (in universal motors). In many twin tub washing machines: • The motor that drives the wash drum (the agitator) runs at a lower speed. Its construction typically includes a winding arrangement or a higher number of poles thereby limiting its rotational speed. • The motor that drives the spin cycle often has fewer poles or is built as a universal motor that can run at higher speeds. Thus, by designing the motors with a different number of poles (or appropriate winding designs), the manufacturer ensures that one motor operates at a relatively low speed (for washing/agitator action) and the other at a higher speed (for efficient spinning). 1.4 Two Electrical Protection Devices Commonly Used in Stove Wiring Typical protection devices incorporated in stove wiring include: • Fuses – which interrupt the circuit if excess current (or a short circuit) occurs. • Thermal cut-outs/thermal fuses – temperature sensitive devices that disconnect power if the stove overheats. ────────────────────────────── QUESTION 2 2.1 Correct Ratings for Circuit Breakers in Specified Sub‐Circuits (Note: Actual ratings may follow national wiring standards; the figures given below are based on common practice in many domestic installations.) 2.1.1 Light Subcircuit: A circuit breaker rated at approximately 6 A is normally used (to protect typical lighting circuits). 2.1.2 Socket Subcircuit (“Slove” subcircuit): For power point sockets, a breaker rated around 10 A is commonly employed to handle the loads expected on these circuits. 2.1.3 Geyser Subcircuit: A higher-current breaker is used for geyser circuits; often a 30 A breaker is specified because of the high-power heating element. 2.2 Operating Principle of an Immersion Thermostat in a Geyser An immersion thermostat is a temperature‐sensitive switch immersed in the water of the geyser. Typically it incorporates a bimetallic strip or a thermistor that changes shape (or resistance) as the water temperature increases. When the water exceeds the preset temperature, the bimetal strip snaps or the sensor triggers a change that causes the contacts to open. This breaks the electrical circuit to the heating element, thereby stopping further heating and preventing overheating of the water. When the water cools below a lower threshold (in systems with hysteresis or re-closing capability) the contacts re‐close and allow heating to resume. 2.3 Wiring Diagram of a Geyser Subcircuit A simplified description of a geyser subcircuit wiring diagram is as follows:  • Supply Side (Active/Phase) →   – A circuit breaker (e.g. 30 A)   – An isolator (or switch) for safe maintenance access   – The immersion thermostat (connected in series)   – The heating element of the geyser  • The wiring continues from the heating element back to the Neutral.  • The Protective Earth (ground) is connected to the body of the geyser and any metal parts for safety. In diagram form, you would show:  (Active) --[Breaker]--[Isolator]--[Thermostat]--[Heating Element]-- (Neutral)              |              (Protective Earth connected to the heating element’s casing) ────────────────────────────── QUESTION 3 3.1 Operation of a Sodium Vapour Lamp A sodium vapour lamp produces light by ionising sodium vapor contained within a low‐pressure glass discharge tube. Its operation can be explained as follows: • At startup a high “striking” voltage is applied across the electrodes to initiate an electric arc through an initially rarefied mixture of sodium (and sometimes a small amount of another gas such as neon or mercury to aid ignition). • Once the arc is established, the sodium metal vaporizes and forms a plasma between the electrodes. • Electrons in the plasma collide with sodium atoms, exciting them. When these atoms return to their lower energy states, they emit light at characteristic wavelengths (mainly the strong yellow doublet at about 589 nm). • A ballast (usually inductive) is used in series to limit and regulate the current through the lamp once conduction begins. • After a brief warm-up period, the lamp operates at a stable condition, providing an efficient, nearly monochromatic yellow light. This efficient conversion of electrical energy to light (with relatively little infrared waste) makes sodium vapour lamps common in streetlighting and other applications where high efficiency and penetrating yellow light are desirable. ────────────────────────────── End of Answers Each answer may be expanded or phrased differently according to specific instructions, but the key points above should be covered.