Two waves are described by y1 = 6 cos 180t and y2 = 6 cos 186t, (both in meters). What effective frequency does the resultant vibration have at a point?
a. 92 Hz
b. 183 Hz
c. 6 Hz
d. 3 Hz
e. 366 Hz
b
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The development of contact lenses has transformed the solutions that are available today for vision impairments. However, wearing them also poses several problems that includes the condition of dry eyes due to lack of cooling, oxygenation, and moisturizing or lubrication of cornea, among others. In a development phase of a new protective liquid for contact lenses, the optometrist would like to know rate of heat loss from the anterior chamber of the eye through the cornea and the contact lens. The system is modelled as a partial hollow sphere, as shown in schematic diagram. The inner and outer radius of the cornea are respectively r1=10 mm and r2=12.5 mm, and the outer radius of the fitted contact lens is r3=14.5 mm. The anterior chamber, which contains the aqueous humor that provides
nutrients to the cornea (as the later tissue has no blood vessels), exposes the inner surface of the cornea to a temperature of Ti=36.90C with a convective heat transfer coefficient of h? i=10 W/(m2 K). The thermal conductivity of transparent tissue of cornea is 0.35 W/(m K), and that of the contact lens material is 0.8 W/(m K). The outer surface of the contact lens is exposed to room air at T0=220C and has a convection coefficient of h? 0=5 W/(m2 K). Draw a thermal circuit for the system showing all of the temperature potentials and thermal resistances. Then estimate the rate of heat loss from the anterior eye assuming that steady state exists and eye aperture spherical angle is of 1000
GIVEN
Inner radius of cornea r1=10 mm=0.01 m
Outer radius of cornea r2=12.5 mm=0.0125 m
Radius of contact lens r3=14.5 mm=0.0145 m
Inner cornea temperature Ti=36.90C
Inner convective heat transfer coefficient h?i=10 W/(m2 K)
Conductivity of cornea tissue (k1)=0.35 W/(m K)
Conductivity of lens material (k2)=0.8 W/(m K)
Room air temperature T0=220C
Outer convection coefficient of h?0=5 W/(m2 K)
FIND
Draw thermal circuit showing all temperature potentials and thermal resistances
Estimate rate of heat loss from anterior eye.
ASSUMPTIONS
Steady state conditions persist
Properties remain constant.
Eye is treated as partial hollow sphere sweeping an angle of ? =1000
SKETCH
The presently accepted value of the Hubble constant gives an age of:
A) 4.5 billion years. B) 8-9 billion years. C) 14 billion years. D) 18 billion years. E) 22 billion years.
In a region where the electric field is axial but the charge density is zero, what is Es (if C is some constant)?
A. C/s2 B. C/s C. zero E. Cs F. Cs2 T. None of the above