DC CIRCUIT: BASIC PRINCIPLES

The substation bus bar is made up of 2 inches round copper bars 20 ft long. What is the resistance of each bar if resistivity is 1.724 x 10-6 ohm-cm.

• 7.21 x 10-5 Ω

• 13.8 x 10-6 Ω

• 5.185 x 10-5 Ω

• 2.96 x 10-5 Ω

Determine the resistance of a busbar made of copper if the length is 10 meters long and the cross section is a 4 x 4 cm2 . Use 1.7241 micro ohm-cm as the resistivity.

• 2.121 x 10-4 Ω

• 4.312 x 10-4 Ω

• 3.431 x 10-5 Ω

• 1.078 x 10-4 Ω

A copper wire of unknown length has a resistance of 0.80 ohm. By successive passes through drawing dies, the length of the wire is increased by 2 ½ times its original value. Assuming that resistivity remains unchanged during the drawing process, determine the new value of its resistance.

• 4 ohms

• 3 ohms

• 5 ohms

• 6 ohms

A one-meter rod of 2-cm diameter is drawn until its resistance is 100 times the initial resistance. Its length afterwards is?

• 10m

• 100m

• 12.5m

• 5m

What is the size in square millimeter (mm2 ) is the cable of 250 MCM size?

• 118.656 mm^2

• 126.675 mm^2

• 112.565 mm^2

• 132.348 mm^2

The resistance of a copper wire at 30°C is 50 ohms. If the temperature coefficient of copper at 0°C is 0.00427, what is the resistance at 100°C?

• 72.26 ohms

• 54.25 ohms

• 63.24 ohms

• 58.15 ohms

The resistance of a wire is 126.48 Ω at 100°C and 100 Ω at 30°C. Determine the temperature coefficient of copper at 0°C.

• 0.00427/°C

• 0.00423/°C

• 0.0256/°C

• 0.0258/°C

The insulation resistance of a kilometer of the cable having a diameter of 2 cm and an insulation thickness of 2 cm is 600 ohms. If the thickness of the insulation is increased to 3 cm, find the insulation resistance of the cable.

• 725 ohms

• 850 ohms

• 757 ohms

• 775 ohms

In the American wire gauge, as the number of gauge increases, the diameter of wire ____

• increases

• decreases

• does not change

• become twice

In order to have a good conductor material, such material shall have _____ valence electrons.

• ONE

• FIVE

• MORE THAN 10

• TWENTY ONE