Atomic Nucleus: The atomic number and mass number for calcium-39 are 20 and 39, respectively. How many neutrons are in one atom?

A. 1
B. 19
C. 20
D. 39
E. 59


Answer: B

Physics & Space Science

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A metal-clad electrical heating element of cylindrical shape, as shown in the sketch below, is immersed in water at atmospheric pressure. The element is a 5-cm-OD, and heat generation produces a surface temperature of 300°C. Estimate the heat flux under steady state conditions and the rate of heat generation per unit length.

GIVEN
? Cylindrical, electrical heating element
? Heat generation produces a 300°C surface temperature
FIND
(a) Heat flux
(b) Rate of heat generation
ASSUMPTIONS
? The system operates at atmospheric pressure
? The heater surface is black
SKETCH

PROPERTIES AND CONSTANTS
Inspection of the boiling curve in Figure (9.1) indicates that at 300°C surface temperature, the heating system must operate in the film boiling regime. Hence, a vapor layer covers the surface of the heater and it is appropriate to evaluate the physical properties at the mean film temperature of (100 + 300)/2 = 200°C.
From Appendix 2, Table 35

From Appendix 2, Table 13

Physics & Space Science

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Physics & Space Science