Two long straight parallel wires separated by a distance of 20 cm carry currents of 30 A and 40 A in opposite directions. What is the magnitude of the resulting magnetic field at a point that is 15 cm from the wire carrying the 30-A current and 25 cm from the other wire?
a. 51 ?T
b. 33 ?T
c. 72 ?T
d. 64 ?T
e. 46 ?T
b
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Which of the following diagrams best represents the size of the atomic nucleus relative to the size of the atom?
A) A B) B C) C D) D
Potential Energy: In the figure, +4.0-?C and -4.0-?C point charges are located as shown. Now an additional +2.00-µC point charge is placed at point A. What is the electric potential energy of this system of three charges, relative to infinity? (k = 1/4??0 = 8.99 × 109 N ? m2/C2) 
A. +264 mJ B. -264 mJ C. 0.00 J D. -26.4 mJ E. +26.4 mJ
A 10-V battery is connected to a 15-? resistor and an unknown resistor R, as shown. The current in the circuit is 0.40 A. How much heat is produced in the 15-? resistor in 2.0 min?
a.
0.40 kJ
b.
0.19 kJ
c.
0.29 kJ
d.
0.72 kJ
e.
0.80 kJ
A single-shell-eight-tube-pass heat exchanger is used in a power plant to preheat 55ºF water to 80ºF by using 190ºF hot water and cooling it to 160ºF. If the overall heat exchanger conductance is 400 Btu/hr?ft^2 ?0F and if 1800 lbm/min of 55ºF water is preheated, determine (a) mass flow of the hot water and (b) surface area of the heat exchanger.
What will be an ideal response?