The atomic number is determined by the number of:
a. neutrons and protons
b. neutrons and electrons
c. protons and electrons
d. protons only
e. neutrons only
d
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An electric room heater has been designed in the shape of a vertical cylinder 2-m-tall and 30 cm in diameter. For safety, the heater surface cannot exceed 35°C. If the room air is 20°C, find the power rating of the heater in watts.
GIVEN
• An electric heater in the shape of a vertical cylinder
• Heater height (H) = 2 m
• Heater diameter (D) = 30 cm = 0.3 m
• Room air temperature (T?) = 20°C = 293 K
FIND
• The power rating of the heater (q) in watts
ASSUMPTIONS
• Radiation is negligible
• Heat transfer from the top and bottom of the tank is negligible
SKETCH
PROPERTIES AND CONSTANTS
for dry air at the mean temperature of 27.5°C
Thermal expansion coefficient (?) = 0.00332 1/K
Thermal conductivity (k) = 0.0256 W/(m K)
Kinematic viscosity (?) = 16.4 × 10–6 m2/s
Prandtl number (Pr) = 0.71
A wire carrying a current that placed in a magnetic field will experience a maximum force if the angle between the direction of the current and the direction of the magnetic field is 60°
Indicate whether the statement is true or false
Io's surface volcanism is driven by phase changes of sulfur and its compounds
Indicate whether the statement is true or false
A primary current of 6.0 A exists in an ideal iron-core transformer at a primary voltage of 100 volts. If the current in the secondary is 0.75 A, calculate the output voltage
a. 12.5 V b. 40 V c. 400 V d. 800 V e. 200 V