DC ELECTRIC CIRCUITS - Day 1

Question 1: EE Board April 1992

     An electric kettle was marked 500 W, 230 V found to take 15 minutes to bring 1 kilogram of water at 15 ⁰C to boiling point. Determine the heat efficiency of the kettle.

A. 79.1%

B. 75.3%

C. 72.4%

D. 74.8%

Question 2: EE Board October 1997

     A process equipment contains 100 gallons of water at 25 ⁰C. It is required to bring it to boiling in 10 minutes. The heat loss is estimated to be 5%. What is the kW rating of the heater?

A. 125 kW

B. 252 kW

C. 50.5 kW

D. 207 kW   

Question 3: EE Board October 1989

     A total of 0.8 kg of water at 20 ⁰C is placed in a 1-kW electric kettle. How long a time in minute is needed to raise the temperature of the water to 100 ⁰C?

A. 4.46 min.

B. 5.32 min

C. 6.34 min

D. 4.56 min

Question 4: EE Board October 1998

     How many calories does an electric heater of 100 watts generate per second?

A. 10

B. 23.88

C. 1000

D. 42.25

Question 5: EE Board October 1997

     The electric energy required to raise the temperature of water in a pool is 1000 kWh. If the heat losses are 25%, the heating energy required will be ___.

A. 1111 kWh

B. 1266 kWh

C. 1750 kWh

D. 1333 kWh

Question 6: EE Board April 1992

     An electric heater carries 12 A at 110 V, is submerged in 22.5 lbs of water for 30 minutes. What will be the final temperature of the water if its initial temperature is 35 ⁰F?

A. 135.43 ⁰F

B. 125.42 ⁰F

C. 133.56 ⁰F

D. 128.33 ⁰F

Question 7: EE Board October 1990

     In an electric heater the inlet temperature is 15 ⁰C. Water is flowing at the rate of 300 grams per minute. The voltmeter measuring voltage across the heating element reads 120 volts and an ammeter measuring current taken reads 10 amperes. When steady state is finally reached, what is the final reading of the outlet thermometer?

A. 57.6 ⁰C

B. 68.4 ⁰C

C. 72.6 ⁰C

D. 42.6 ⁰C

Question 8: EE Board October 1991

     Four cubic meters of water is to be heated by means of four 1.5 kW, 230-V immersion heating elements. Assuming the efficiency of the heater as 90%, determine the time required boiling the water if the initial temperature is 20 ⁰C and if all four elements are connected in parallel.

A. 71 hrs

B. 63 hrs

C. 69 hrs

D. 66 hrs

Question 9: EE Board October 1991

     Four cubic meters of water is to be heated by means of four 1.5 kW, 230-V immersion heating elements. Assuming the efficiency of the heater as 90%, determine the time required boiling the water if the initial temperature is 20 ⁰C and if the elements are connected two in series in parallel with two in series.

A. 275.6 hrs

B. 295.3 hrs

C. 252.2 hrs

D. 264.4 hrs

Question 10: EE Board April 1997

     A circuit consisting of three resistors rated: 10 ohms, 15 ohms and 20 ohms are connected in delta. What would be the resistances of the equivalent wye connected load?

A. 0.30, 0.23 and 0.15 ohm

B. 3.0, 4.0 and 5.0 ohms

C. 3.33, 4.44 and 6.66 ohms

D. 5.77, 8.66 and 11.55 ohms

Question 11: EE Board October 1994

     The equivalent wye element of 3 equal resistors each equal to R and connected in delta is

A. R

B. 3/2R

C. R/3

D. 3R

Question 12:

     Three resistors of 6-ohm resistance are connected in delta. Inside the delta another three 6-ohm resistors are connected in wye. Find its resistance between any two corners.

A. 2 ohms

B. 3 ohms

C. 4 ohms

D. 1 ohm