FIVE PROBLEMS ON HEATING EFFECT OF ELECTRIC CURRENT
PROBLEM
– 01
An
electric oven has 3 heating elements of resistance 25 ohms each. They can be
switched all in series or all in parallel. Calculate the rate of production of
heat in calories per second in both cases when the supply voltage is 230 V.
PROBLEM
– 02
An
immersion water heater takes 30 minutes to heat 60 kg of water from 20 degree
centigrade to boiling point. Calculate the power rating of the heater, assuming
the heating equipment to have an efficiency of 90 percent.
PROBLEM
– 03
A
storage electric water heater is required to raise the temperature of 20 kg
water from 20 degree centigrade to 80 degree centigrade in 45 minutes.
Calculate the resistance of the heating element if the heater is to be used on
a 230 V supply. Assume the efficiency of heater is 90 percent.
PROBLEM
– 04
A
soldering iron is rated at 25 watts when connected to a 75 watts when connected
to a 230 V supply. If the soldering iron takes 5 minutes to heat a working
temperature of 150 centigrade from 20 degree centigrade find the mass, assuming
it to be made of copper. Specific heat capacity of copper is 390 J/k°C.
PROBLEM
– 05
An
electric kettle raises the temperature of 2 kg liters of water from 20 degree
centigrade to 80 degree centigrade. If the efficiency of the heater is 85
percent. Calculate the energy consumed by the heater (a) in joules (b) in kWh.
The specific heat capacity of the water 4190 J/KgK.
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