PROBLEM
– 01
An
electric iron has a rating of 1.5 kW at 220 V and works for 10 hours a day, 26
days in a month. Calculate the current taken and for resistance of its heating
element. Also, calculate the cost of electrical energy consumed in one month,
if the cost of one kWh is Rs.2.25.
A
2 hp motor has an efficiency of 85 percent. What is (a) its electric power
input in watts, (b) its energy consumption if it runs continuously for 10
hours, (c) the cost of energy consumption if the cost per unit is Rs.2.25 and
(d) the current carrying capacity of its connecting wire, if it is operating
from a 220 V supply.
PROBLEM
– 03
A
250 ton train experiences wind resistance equivalent to 62.5 N/t. The operating
efficiency of the driving motors 0.87 and the cost of electrical energy is Rs. 7.50
per unit. What is the cost of the energy required to make the train travel 1
km. If the train is supplied at a constant voltage of 2 kV and travels with a
velocity of 80 km/h, what is the supply current?
PROBLEM
– 04
An
electric furnace is being used to melt 20 kg aluminium. The initial temperature
of aluminum is 20 degree centigrade. Assume the melting point of aluminum to be
660 degree centigrade, its specific heat capacity to be 950 J/kg/ºC and its
specific heat of latent heat of fusion to be 387000 J/kg. Calculate the power
required to finish the conversion in 40 minutes, assuming the efficiency of
conversion to be 80 percent. What is the cost of energy consumed if t cost of
1kWh is eighty rupee?
PROBLEM
– 05
A
diesel-electric generator set supplies an output of 50 kW. The calorific value
of the fuel oil used is 10874.5 Kcal/kg. If the overall efficiency of the unit
is 65 percent. Calculate (i) the mass of oil required per hour (ii) the electric
energy generated per kg of diesel.
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