Two speakers are placed side by side and driven by the same frequency of 0.50 kHz. If the distance from a person to one speaker is 5
0 m and the person detects little or no sound, which of the following is a possible the distance from the person to the other speaker? The sound speed in the room is 340 m/s. A) 7.7 m
B) 8.1 m
C) 8.4 m
D) 9.1 m
B
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Vision Problems: A farsighted girl has a near point at 2.0 m but has forgotten her glasses at home. The girl borrows eyeglasses that have a power of +2.75 diopters. With these eyeglasses, what is the near point of the girl, assuming that she wears them extremely close to her eyes?
A. 28 cm B. 31 cm C. 33 cm D. 37 cm E. 40 cm
The direction of the force on a current-carrying wire in a magnetic field is
A) in the direction opposite to the current. B) perpendicular only to the current. C) perpendicular only to the magnetic field. D) in same direction as the current. E) perpendicular to both the current and the magnetic field.
To determine the thermal conductivity of a long, solid 2.5 cm diameter rod, one half of the rod was inserted into a furnace while the other half was projecting into air at 27°C. After steady state had been reached, the temperatures at two points 7.6 cm apart were measured and found to be 126°C and 91°C, respectively. The heat transfer coefficient over the surface of the rod exposed to the air was estimated to be 22.7 W/(m2 K). What is the thermal conductivity of the rod?
GIVEN
FIND
The thermal conductivity (k) of the rod
ASSUMPTIONS
Uniform thermal conductivity
One dimensional conduction along the rod
The rod approximates a fin of infinite length protruding out of the furnace
SKETCH
The cosmic background radiation appears compatible with a blackbody source at what temperature?
a. 0.0003 K c. 300 K b. 3 K d. 0.03 K