DC ELECTRIC CIRCUITS - Day 5

Question 1: EE Board October 1997

     A load of 10 ohms was connected to a 12-volt battery. The current drawn was 1.18 amperes. What is the internal resistance of the battery?

A. 0.35 ohm

B. 0.20 ohm

C. 0.25 ohm

D. 0.30 ohm

Question 2:

     The potential at the terminals of the battery falls from 9 V on open circuit to 6 volts when a resistor of 10 ohms is connected across its terminals. What is the internal resistance of the battery?

A. 5Ω

B. 4Ω

C. 3Ω

D. 2Ω

  

Question 3: EE Board April 1997

     The electromotive force of a standard cell is measured with a potentiometer that gives a reading of 1. 3562 V. When a 1.0 megaohm resistor is connected across the standard cell terminals, the potentiometer reading drops to 1.3560 V. What is the internal resistance of the standard cell?

A. 174.5 ohms

B. 145.7 ohms

C. 147.5 ohms

D. 157.4 ohms

Question 4:

     A battery is formed of five cells joined in series. When the external resistance is 4 ohms, the current is 1.5 A and when the external resistance is 9 ohms, the current falls to 0.75 A. Find the internal resistance of each cell.

A. 0.5 ohm

B. 1.0 ohm

C. 0.2 ohm

D. 0.3 ohm

Question 5: EE Board April 1988

     A Barangay power station supplies 60 kW to a load over 2,500 ft, 100 mm², two-conductors copper feeder, the resistance of which is 0.078 ohm per 1000 ft. The bus bar voltage is maintained constant at 600 V. Determine the load current.

A. 105 A

B. 108 A

C. 110 A

D. 102 A

Question 6:

     A 120 V DC motor draws current of 100 A and is located 1000 ft from the supply source. If the diameter of the copper transmission line is 0.45 inch, what must be the voltage of the supply?

A. 125.32 V

B. 130.24 V

C. 129.32 V

D. 127.05 V

Question 7: EE Board October 1986

     A LRT car, 5 km distance from the Tayuman, takes 100 A over a 100 mm hard drawn copper trolley wire having a resistance of 0.270 ohm per km. The rail and ground return has a resistance of 0.06 ohm per km. If the station voltage is 750 V, what is the voltage of the car?

A. 585 V

B. 590 V

C. 585 V

D. 590 V

Question 8:

     The hot resistance of an incandescent lamp is 10 ohms and the rated voltage is 50 V. Find the series resistance required to operate the lamp from an 80 V supply.

A. 8Ω

B. 4Ω

C. 6Ω

D. 10Ω

Question 9:

A resistive coil draws 2 A at 110 V after operating for a long time. If the temperature rise is 55 ⁰C above the ambient temperature of 20 ⁰C, calculate the external resistance which must be initially connected in series with the coil to limit the current to 2 A. The temperature coefficient of the material of the coil is 0.0043 per ⁰C at 20 ⁰C.

A. 10.12 ohms

B. 10.52 ohms

C. 11.45 ohms

D. 12.05 ohms

Question 10:

A carbon resistor dissipates 60 W of power from a 120 V source at 20 ⁰C. How much power will be dissipated in the resistor at 120 ⁰C if connected across the same source? Assume the temperature coefficient of carbon at 20^thC is -0.0005 per ⁰C.

A. 61.50 W

B. 65.21 W

C. 62.34 W

D. 63.16 W