An advantage of low voltage switching is
a) that local and remote control of lights is permitted
b) the wiring does not require conduits
c) changes are simple and economical
d) a and b are correct
e) a, b and c are correct
Answer: E
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Power Engineering
- The work done in a constant pressure expansion can be determined by:
- If 10.4 m³ of air is compressed at a constant temperature to 5.1 m³ and 750 kPa gauge. Calculate how much work is done on the gas, assuming atmospheric pressure to be 100 kPa.
- Boyle's Law is one of constant:
- The pressure-volume diagram of a typical air compressor will have a curve drawn:
- If the volume of a confined gas is constant then the absolute pressure is directly proportional to the absolute temperature according to:
- Find the characteristic constant for a gas if 112 kg of the gas has a volume of 5.7 m³ at 1500 kPa absolute and 27.5°C.
- If 24,500 kJ of work is done in a cylinder when 115 kg of a perfect gas is expanded isothermally at 210°C from 0.035 m³ to 6.9 m³. Find the characteristic constant for this gas.
- A gas at 1000 kPa gauge pressure and 30°C is transferred from a cylindrical vessel 1.5 m in diameter and 3 m long to another cylindrical vessel 2.5 m in diameter and 5 m long. If the new gauge pressure is 150 kPa, calculate the new temperature. Note: Assume atmospheric pressure to be 100 kPa for this calculation.
- If 0.25 m³ of a gas at 4000 kPa gauge pressure is expanded until the gauge pressure is 500 kPa and the expansion is polytropic with n = 1.35. Find the final volume the gas will occupy. Note: Assume atmospheric pressure = 100 kPa
- The equation (PV/T) = mR or PV = mRT is called the:
- The Characteristic Constant of each perfect gas is
- The pressure-volume diagram of a typical air compressor will have a curve drawn:
- If 10.4 m³ of air is compressed at a constant temperature to 5.1 m³ and 750 kPa gauge. Calculate how much work is done on the gas, assuming atmospheric pressure to be 100 kPa.
- Compression and expansion in real life cases will always follow the polytropic process that is described by the formula(s):
- The formula Work = (P1V1 - P2V2) / n - 1 is used to describe expansion during:
- To "expand a gas" means the gas is:
- The work done in a constant pressure expansion can be determined by:
- A perfect gas is compressed under conditions of constant temperature to a volume of 30 m³. If the final pressure of the gas is 450 kPa gauge and the initial volume was 135 m³, what was the initial pressure? (Assume atmospheric pressure to be 101.3 kPa)
- Gases such as air, nitrogen and oxygen can be roughly defined as perfect gases because they:
- The General Gas Law can be written using the formula/s:
- The pressure-volume diagram of a typical air compressor will have a curve drawn:
- Absolute pressure can be defined as:
- How much work is required to compress a gas polytropically from 195 kPa abs to 1600 kPa abs while reducing the volume to 0.8 m3? Use the value of "n" for this gas as 1.35.
- If 1.45 m³ of air at 100 kPa abs and 12°C is compressed to 950 kPa abs while following the law PV1.34 = C. Taking R for air = 0.287 kJ/kg K, find the final volume of air and the mass of air compressed.
- The characteristic constant for a gas is given as: