A beam of light with a frequency range of 3.01 × 1014 Hz - 6.10 × 1014 Hz is incident on a metal surface. If the work function of the metal surface is 2.20 eV, what is the maximum kinetic energy of photoelectrons ejected from this surface?
A)
0.32 eV
B)
0.21 eV
C)
0.42 eV
D)
0.16 eV
E)
0.48 eV
A
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In a biomedical processing plant, a newly developed liquid drug or medication that leaves a mixing chamber at 20°C needs to be heated to 70°C in a thermal curing process. This is achieved by heating the liquid media at the rate of 10 kg/h in a thin metallic circular pipe with a 10 mm inner diameter that is electrically heated by wrapping it in resistance wire and insulation. If the tube surface is heated with a constant heat flux of 5,100 W/m2, calculate the length of tubing needed for this heat exchange device and the inner surface temperature of the pipe at its exit. Assume fully developed convection, and verify this assumption after calculating the length. The physical properties of the fluid media are considered as follows: Cp= 4.0 kJ/(kg K), k= 0.5 W/(m K), ?= 0.002 Ns/m2, and
?=1000 kg/m3 GIVEN • Diameter of copper tube (Di)= 10 mm = 0.01 m • Cooling water inlet temperature (Tin)= 200C • Cooling water flow rate ( m• )=10 kg/hr = 2.78*10-3 kg/s • Cooling water outlet temperature (Tout)= 700C • Surface heat flux(q’’) = 5100 W/m2 FIND (a) Length of tubing needed for this heat exchange device. (b) Inner surface temperature of pipe at exit. PROPERTIES AND CONSTANTS Given, for the fluid Density (?) = 1000 kg/m3 Specific heat (cp) = 4000 J/(kg K) Thermal conductivity (k) = 0.5 W/(m K) Absolute viscosity (?) = 0.002 (Ns)/m2
Which hypothetical universe will eventually contract, if there were no dark energy?
A) the universe with 1.5 times the critical density of matter B) the universe with 1.0 times the critical density of matter C) the universe with 0.5 times the critical density of matter
Both ends of a 0.6-cm copper U-shaped rod, are rigidly affixed to a vertical wall as shown in the accompanying sketch. The temperature of the wall is maintained at 93°C. The developed length of the rod is 0.6 m, and it is exposed to air at 38°C. The combined radiation and convection heat transfer coefficient for this system is 34 W/(m2 K). (a) Calculate the temperature of the midpoint of the rod. (b) What will the rate of heat transfer from the rod be?
GIVEN
FIND
(a) Temperature of the midpoint (TLf)
(b) Rate of heat transfer from the rod (M)
ASSUMPTIONS
The system is in steady state
Variation in the thermal conductivity of copper is negligible
The U-shaped rod can be approximated by a straight rod of equal length
Uniform temperature across any section of the rod
SKETCH
Air resistance on a high-speed projectile shortens its
A) range. B) maximum height. C) both of these D) none of the above