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Basic Electrical Questions and Answers

These questions are primarily related to Capacitance, Electric Current, Resistors in Series and Parallel. These topics are covered in detail here:

Capacitance

Electric Current

Series and Parallel Circuit

 
  1. Determine the voltage when 500 J of energy is used to move 10 C of charge.

              V= W/C = 500 J/10 C = 50 V

  1. A certain voltage sine wave goes through 5000 cycles in 2 seconds. Determine the frequency.

             f = 5000 cycles/2 sec = 2500 cycles/s = 2500 Hz

  1. The frequency of the ac utility voltage is 60 Hz. What is the period?

             T = 1/f = 1/60 Hz = 0.0167 sec = 16.7 ms

  1. Determine the current when 50 coulombs of charge move past a point in 0.5 seconds.

             I = Q/t = 50 C/0.5 s = 100 A

  1. What is the equivalent dc voltage for 50 V rms,

              Vdc = 50 V

  1. Find the resistance of 50 feet of 14 gauge wire.

            R = 50 ft x 2.525 Q/1000 ft = 0.126 Q

  1. Calculate the voltage across a 10 Q resistor if the current is 1.5 A.

             V= IR = (10 Q)(1.5 A) = 15 V

  1. Calculate the current through a 33 Q resistor if there is 12 V across it.

            I = V/R = 12 V/33 W = 0.364 A

  1. Calculate the resistance if V = 24 V and I = 1.2 A.

            R = V/I = 24 V/1.2 A = 20 Q

  1. How much energy is dissipated when a 100 W light bulb is on for 24 hours?

           W = Pt = (100 W) 24 h = 2400 Wh

  1. Determine the power in each of the resistances in Problems 7, 8, and 9.

          P = I2R = (1.5 A)210 Q = 22.5 W

         P = V2/R = (12 V) 2/33 Q = 4.36 W

         P = VI = (24 V) (1.2 A) = 28.8 W

  1. Find the total resistance for the following resistors in series: 10 Q, 47 Q, 75 Q, and 100 Q.

         RTOT = 10 Q + 47 Q + 75 Q + 100 Q = 232 Q

  1. If the resistors in Problem 12 are connected in parallel, what is the total resistance?

          Rtot = 1/ (1/10 Q + 1/47 Q + 1/75 Q + 1/100 Q) = 6.92 Q

  1. Assume a solar cell produces 0.5 V at peak sunlight. If a total of 12 V needed, what is the minimum number of solar cells required and how must they be connected?

           Number of cells = 12 V/0.5 V/cell = 24 cells connected in series.

  1. How would you triple the current capacity of the solar cell array in Problem 14, keeping the same voltage?

          To triple the current, connect in parallel three groups of 24 series-connected cells.

  1. Determine the energy stored by a 10 F capacitor with 24 V across it.

            W = (1/2)CV2 = (1/2)(10 F)(24 V)2 = 2880 J

  1. Determine the power dissipated if 25 V is measured across a 100 Q resistance.

         P = V2/R = (25 V)2/100 Q = 6.25 W

  1. What is the ampacity of an AWG 6 copper wire?

        Ampacity = maximum current = 37 A

  1. Find the resistance for 500 ft. of an AWG 18 copper wire.

         R = (500 ft) (6.385 Q/1000 ft) = 3.19 Q

  1. Determine the minimum fuse rating required for an electric heater that operates on 120 V and the power in the heater is 1200 W.

        I = P/V = 1200 Q/120 V = 10 A minimum fuse rating

About Ahmed Faizan

Mr. Ahmed Faizan Sheikh, M.Sc. (USA), Research Fellow (USA), a member of IEEE & CIGRE, is a Fulbright Alumnus and earned his Master’s Degree in Electrical and Power Engineering from Kansas State University, USA.

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