Ee-1-for-lms-problems.docx

1. A certain copper wire has a resistance of 25 ohms at 10°C. Take the temperature coefficient at 10°C to be 0.00409 deg/C. What must be the maximum operating temperature of the wire if its resistance is to increase by at most 20%? a. 58.89 c. 59.24 b. 60.13 d. 59.25 2. A single-phase transmission line 90 km is made up of hard drawn copper 500 mils in diameter. If the resistivity of the hard drawn copper at 20°C is 1.77 x 10 -8 ohm-meter. Determine the loop resistance at 20°C. a. 0.1394 ohm/km c. 0.546 ohm/km b. 1.348 ohm/km d. 0.434 ohm/km 3. A capacitor is charged at 100 000 micro-coulomb in 2 seconds. What is the current in mA? a. 0.5 c. 5 b. 0.005 d. 50 4. Copper has resistivity of 16 ohm-nm at zero degrees centigrade. What is its temperature coefficient of resistance at zero degrees centigrade? a. 3.93 x 10-3 /°C c. 4.27 x 10 -3 /°C b. 3.65 x 10-3 /°C d. 2.73 x 10-3 /°C 5. Two resistors when connected in series has a total resistance of 40 ohms and when connected in parallel has a total resistance of 7.5 ohms. Find the value of each resistance. a. 24 & 16 c. 20 & 20 b. 30 & 10 d. 12 & 28 -5 6. A wire has a resistance of 0.75 ohm per ft. at an area 10 m2. Determine the resistance of a 200 ft long conductor if the area is 3 x 10-5 m2. a. 2.5 c. 50 b. 25 d. 12.5 7. A copper has a resistance of 2.4 ohms at 20°C. Find its resistance at 75°C. Resistance temperature coefficient at 20°C is 0.034/°C. a. 3.78 ohms c. 12.18 ohms b. 6.89 ohms d. 7.48 ohms 8. The resistance of length of copper wire is 2.6 ohms at 20°C. The temperature coefficient of resistance at 20°C for copper is 0.00393/°C. What is the resistance at 75°C? a. 3.670 ohms c. 11.38 ohms b. 3.162 ohms d. 4.378 ohms 9. A 110 V dc motor draws current of 30 A and is located 500 ft from the power source. What is the supply voltage if the diameter of the copper wire is 0.25 inch? a. 119 V c. 121 V b. 117 V d. 115 V 10. A light bulb having a tungsten filament, draws 0.5A at 110 V. the cold resistance of the filament is 20 ohms at 20 °C. at this temperature the temperature coefficient of resistance for tungsten is 0.005 per °C. Determine the operating temperature of the bulb. A. 1220°C B. 520°C C. 2520°C D.2020 °C