LC Circuits: A series circuit contains an 80-?F capacitor, a 0.020-H inductor, and a switch. The resistance of the circuit is negligible. Initially, the switch is open, the capacitor voltage is 50 V, and the current in the inductor is zero. At time t = 0 s, the switch is closed. When the potential across the capacitor is 30 V, what is the rate of change of the current?
A. 1000 A/s
B. 1500 A/s
C. 2000 A/s
D. 2500 A/s
E. 3000 A/s
Answer: B
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How large a force is necessary to stretch a 2.0 mm radius steel wire (Y = 2.0 × 10^11 N/m2) by 2.0%?
a. 5.0 × 10^4 N c. 2.5 × 10^3 N b. 2.5 × 10^4 N d. 1.3 × 10^4 N
A shell-and-tube heat exchanger is to be used to cool 25.2 kg/s of water from 38°C to 32°C. The exchanger has one shell-side pass and two tube side passes. The hot water flows through the tubes and the cooling water flows through the shell. The cooling water enters at 24°C and leaves at 32°C. The shell-side (outside) heat transfer coefficient is estimated to be 5678W/(m 2 K). Design specifications require that the pressure drop through the tubes be as close to 13.8 kPa as possible and that the tubes be 18 BWG copper tubing (1.24 mm wall thickness), and each pass is 4.9 m long. Assume that the pressure losses at the inlet and outlet are equal to one and one half of a velocity heat (?V2/gc), respectively. For these specifications, what tube diameter and how many tubes are needed?
GIVEN
A water-to-water shell-and-tube exchanger, hot water in tubes, cooling water in shell One shell and two tube passes Hot water flow rate m
h= 25.2 kg/s Water temperatures
? Hot: Th,in = 38°C Th,out = 32°C
? Cold: Tc,in = 24°C Tc,out = 32°C Shell-side transfer coefficient h o= 5678 W/(m2 K) Pressure drop (?p) = 13.8 kPa Tube wall thickness (t) = 1.24 mm = 0.00124 m Tube length per pass (Lp) = 4.9 m
FIND
The tube diameter (Do) and number of tubes (N)
ASSUMPTIONS
Pressure losses at inlet and outlet (?pii) = 1.5 (? V2/gc) Variation of thermal properties with temperature is negligible Fouling resistance is negligible Thermal resistance of the tube walls is negligible
SKETCH
PROPERTIES AND CONSTANTS
for water at 30°C Density (?) = 995.7 kg/m3
Specific heat (cp) = 4176 J/(kg K)
Thermal conductivity (k) = 0.615 W/(m K)
Kinematic viscosity (?) = 0.805 × 10–6 m2/s
Prandtl number (Pr) = 5.4
Light with a wavelength of 310 nm is incident on a metal that has a work function of 3.80 eV. What is the maximum kinetic energy that a photoelectron ejected in this process can have?
(1 eV = 1.60 × 10-19 J, c = 3.00 × 108 m/s, h = 6.626 × 10-34 J ? s) A) 0.62 × 10-19 J B) 0.21 × 10-19 J C) 0.36 × 10-19 J D) 0.48 × 10-19 J E) 0.33 × 10-19 J
Jane says that the magnitude of the torque exerted by a force of magnitude F is equal to the perpendicular distance from the axis of rotation r multiplied by F, while Jason insists that it is equal to the distance from the axis of rotation r
multiplied by the magnitude of the perpendicular component of the force, F Who is right?