# Ah Beng and his wile Just bought a ready studio

Ah Beng and his wile Just bought a ready studio house In the MesaHl spartment. His wie
lovee to prepare dishes and wiehes to have a complete set of ididhen applianoes. However,
Ah Beng works as a construction worker with limilted Income. Owing to COVID-19 pandemic,
his salary eventuelly being cut by his company. To satisly his wife's expectation, he wert to
a nearby second-hand electrical store and purchased some kltchen appliances, As electrical
upplianoes aged, the efficlency (7) of the electrioal appliunces will be < 100% with old wires,
electrical droults, resistors, and other bullt-in electrical components.
x 100%
nWetactual)
: Efciency (%)
Wecdeoty: Ideal required electrical power (W)
Walactua: Actual required electrical power (W)
For all his electrical appliances, the specifications are summarized in the table below:
appliances, the specifications are summarized in the table below:
No.
Appliance
Efficiency, n (%)
Voltage, V (V)
Current, I (A)
Resistance, R (2)
Microwave oven
75
N/A
5.4
22.22
Air fryer
88
220
N/A
32.84
Rice cooker
95
240
3.3
N/A
Pressure cooker
94
220
7.5
N/A
Blender
89
N/A
5.8
20.69
Refrigerator
83
200
N/A
30.30
Steam cooker
77.7
200
4.4
N/A
8.
Bread maker
92
230
8.3
N/A
* N/A: Not available.
(a) Calculate the ideal required electrical powers of all the electrical appliances.
[8 marks]
[4 marks]
(b) Calculate the actual required electrical powers of all the appliances.
(c) If the kitchen could be modelled as a closed and adiabatic system, calculate the rate of
[4 marks]
energy change of the kitchen if all the appliances are in used concurrently.
(d) If the kitchen can be modelled as a closed but non-adiabatic system, calculate the heat
a rate of energy change of 5750 W when only microwave oven, air fryer, rice cooker, and
[4 marks]
transfer rate and determine its direction (in or out of the kitchen) if the kitchen is experiencing
refrigerator are in used.
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