EXAM1 - ECE311
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Marist Brothers First Trinal Examinations Notre Dame of Kidapawan College July 14-16, 2015 First Semester, SY 2015-2016 ECE311 – Circuits 1 Kidapawan City Mar Lou P. Galinato, ECE, MEP Name: _______________________ __________________ Program/Year: _____________________ PROBLEM SOLVING [100 PTS] Show your solution (detailed) to the following items. Write your answer on provided newsprints. [1] Electric current is measured in amperes (A). If an ampere is expressed as a flow of charge in coulombs per second (C/s), how many electrons pass a given point in 30 s in a conductor carrying 8-A current. The charge on an ele ctron is approximately 1.6 × 10 −9 C. [2] The unit of force is the newton (N) and work is measured in netwon-meters (N·m), which is also the unit of energy. Alternatively, energy is expressed in joules (J), where 1 J = 1 N·m. Determine the work done in moving a 50-µC electric charge (Q) through a distance of 50 cm in the direction of a uniform electric field (E) of 50 kV/m, if the force F is given by = . [3] Power is defined as the rate of work done or the rate of energy conversion. Thus, the unit of power is the joule per second (J/s) which is equal to one watt (W). If the time taken to move the 50-µC charge of Prob. [2] through 50 cm is 10 ms, calculate the corresponding power. [4] We observed in Prob. [2] that an electric charge experiences a force in an electric field. Electric potential difference (between two points) is measured in volt (V), and is defined as the work done in moving a unit positive charge (from one point to the other). What is the potential difference between two points if it requires 220 µJ to move a 10-µC charge from one point to the other? [5] A car battery supplies 48 J of energy at 12 V over a ce rtain period of time. Determine the charge moved during this period. [6] Electric utilities employ as the unit of energy the kilowatt-hour (kWh). The power consumed in a household over a 24-h period is as follows: 8 AM to 2 PM (1.5 kW); 2 PM to 6 PM (4.5 kW); 6 PM to 11 PM (2.6 kW); and 11 PM to 8 AM (1.0 kW). What is the energy consumption in mega-joules? [7] A copper conductor of circular cross section 5 mm in diameter is 5 m long. Calculate its resistance at 20°C if the resistivity of copper at 20°C is 1. 72 × 10 −8 Ω·m. [8] A transmission line cable consists of 19 strands of identical copper conductors, each 1.5 mm in diameter. The physical length of the ca ble is 2 km. But, because of the twist of each strand, the actual lengths of the conductors are increased by 5 percent. What is the resistance of the cable? Resistivity of copper is 1.72 × 10 −8 Ω·m. [9] We have two resistors wound with round copper wire. The length and the diameter of the first wire are ℓ and A respectively and those of the second wire are 0.25 ℓ and 0.5A. Determine the ratios of currents and powers for the two resistors if they are connected across the same voltage source. [10] The energy capacity or rating of a battery is generally expressed in ampere -hour (Ah). A battery is required to supply 0.5 A continuously for three days. What must be the rating of the battery? -x-x-x-x-x-x- x-x- NOTHING FOLLOWS -x-x-x-x- x-x-x-x-
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EXAM1 - ECE311
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Marist Brothers First Trinal Examinations Notre Dame of Kidapawan College July 14-16, 2015 First Semester, SY 2015-2016 ECE311 Circuits 1 Kidapawan City Mar Lou P. Galinato, ECE, MEP Name: _________________________________________ Program/Year: _____________________ PROBLEM SOLVING [100 PTS] Show your solution (detailed) to the following items. Write your answer on provided newsprints.
[1] Electric current is measured in amperes (A). If an ampere is expressed as a flow of charge in coulombs per second (C/s), how many electrons pass a given point in 30 s in a conductor carrying 8-A current. The charge on an electron is approximately 1.6 1019 C.
[2] The unit of force is the newton (N) and work is measured in netwon-meters (Nm), which is also the unit of energy. Alternatively, energy is expressed in joules (J), where 1 J = 1 Nm. Determine the work done in moving a 50-C electric charge (Q) through a distance of 50 cm in the direction of a uniform electric field (E) of 50 kV/m, if the force F is given by = .
[3] Power is defined as the rate of work done or the rate of energy conversion. Thus, the unit of power is the joule per second (J/s) which is equal to one watt (W). If the time taken to move the 50-C charge of Prob. [2] through 50 cm is 10 ms, calculate the corresponding power.
[4] We observed in Prob. [2] that an electric charge experiences a force in an electric field. Electric potential difference (between two points) is measured in volt (V), and is defined as the work done in moving a unit positive charge (from one point to the other). What is the potential difference between two points if it requires 220 J to move a 10-C charge from one point to the other?
[5] A car battery supplies 48 J of energy at 12 V over a certain period of time. Determine the charge moved during this period.
[6] Electric utilities employ as the unit of energy the kilowatt-hour (kWh). The power consumed in a household over a 24-h period is as follows: 8 AM to 2 PM (1.5 kW); 2 PM to 6 PM (4.5 kW); 6 PM to 11 PM (2.6 kW); and 11 PM to 8 AM (1.0 kW). What is the energy consumption in mega-joules?
[7] A copper conductor of circular cross section 5 mm in diameter is 5 m long. Calculate its resistance at 20C if the resistivity of copper at 20C is 1.72 108m.
[8] A transmission line cable consists of 19 strands of identical copper conductors, each 1.5 mm in diameter. The physical length of the cable is 2 km. But, because of the twist of each strand, the actual lengths of the conductors are increased by 5 percent. What is the resistance of the cable? Resistivity of copper is 1.72 108 m.
[9] We have two resistors wound with round copper wire. The length and the diameter of the first wire are and A respectively and those of the second wire are 0.25 and 0.5A. Determine the ratios of currents and powers for the two resistors if they are connected across the same voltage source.
[10] The energy capacity or rating of a battery is generally expressed in ampere-hour (Ah). A battery is required to supply 0.5 A continuously for three days. What must be the rating of the battery?
-x-x-x-x-x-x-x-x- NOTHING FOLLOWS -x-x-x-x-x-x-x-x-
