The boundary shown is that of a uniform magnetic field directed in the positive z direction. An electron enters the magnetic field with a velocity pointing along the x axis and exits 0.63 ?s later at point A. What is the magnitude of the magnetic field?
a.
18 ?T
b.
14 ?T
c.
28 ?T
d.
34 ?T
e.
227 ?T
b
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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
Double-Slit Interference: Coherent light of wavelength 540 nm passes through a pair of thin slits that are 3.4 × 10-5 m apart. At what angle away from the centerline does the second bright fringe occur?
A. 1.8° B. 3.7° C. 4.3° D. 1.5° E. 5.0°
The primary of an ideal transformer has 100 turns and its secondary has 200 turns. Neglecting frictional losses, if the power input to the primary is 100 W, we can expect the power output of the secondary to be
A) 100 W. B) 50 W. C) 200 W. D) none of the given answers.
Which of the following scenarios correctly demonstrates the transformation of mass into energy as given by Einstein's equation, E = mc2?
A) When hydrogen is fused into helium, whether in the Sun or in a nuclear bomb, the mass difference is turned into energy. B) An object accelerated to a great speed has a lot of kinetic energy. C) A mass raised to a great height has a lot of gravitational potential energy. D) When you boil a pot of water, it has a high heat content, or thermal energy. E) A burning piece of wood produces light and heat, therefore giving off radiative and thermal energy.