A 0.13-m string, fixed at both ends and vibrating in its n = 4 harmonic, excites a pipe that is long and open at both ends, into its second overtone resonance
What is the speed of transverse waves on the string? The speed of sound in air is 345 m/s.
A) 30 m/s B) 38 m/s C) 36 m/s D) 32 m/s E) 34 m/s
B
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Two loudspeakers are placed side by side and driven by the same source at 525 Hz. A listener is positioned in front of the two speakers and on the line separating them, thus creating a constructive interference at the listener's ear. If one of the speakers is gradually pushed toward the listener, how far must it be moved to repeat the condition of constructive interference at the listener's ear?
(The speed of sound = 340 m/s.) a. 1.5 m b. 0.65 m c. 0.32 m d. 0.16 m e. 3.1 m
Refracting Telescope: A student constructs an astronomical telescope and wishes it to have a magnification of 10. If the telescope has an objective lens of focal length 0.50 m, what must be the focal length of the eyepiece?
A. 2.5 cm B. 5.0 cm C. 10 cm D. 25 cm
The test data tabulated on the next page were reduced from measurements made to determine the heat-transfer coefficient inside tubes at Reynolds numbers only slightly above transition and at relatively high Prandtl numbers (as associated with oils). Tests were made in a double-tube exchanger with a counterflow of water to provide the cooling. The pipe used to carry the oils was 1.5 cm-OD, 18 BWG, 3 m-long. Correlate the data in terms of appropriate dimensionless parameters.
Hint: Start by correlating Nu and ReD irrespective of the Prandtl numbers, since the influence of
the Prandtl number on the Nusselt number is expected to be relatively small. By plotting Nu vs.
Re on log-log paper, one can guess the nature of the correlation equation, Nu = f1 (Re). A plot of
Nu/f1 (Re) vs. Pr then reveals the dependence upon Pr. For the final equation, the influence of
the viscosity variation also is considered.
GIVEN
Oil in a counterflow heat exchanger
Pipe specifications: 1.5 cm-OD, 18 BWG
Pipe length (L) = 3 m
The experimental data above
FIND
Correlate the data in terms of appropriate dimensionless parameters
ASSUMPTIONS
The data represents the steady state for each case
PROPERTIES AND CONSTANTS
From Appendix 2, Table 42: for 1.5 cm OD, 18 BWG tubing, the inside diameter D = 1.338 cm
Magnetic fields are produced by
a. constant electric currents. b. electric currents that vary sinusoidally with time. c. time-varying electric fields. d. all of the above. e. only (a) and (b) above.