Describe our location in the Milky Way
What will be an ideal response?
We lie in a spiral arm about 30,000 ly (8 kp) out from the galactic center, and in the disk of the galaxy.
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A(n) ____________________ telescope has an objective that is a lens
Fill in the blank(s) with correct word
Resolution: The pupil of a person's eye changes from a diameter of 3.5 mm to 1.5 mm as the illumination is increased. By what factor does the minimum angle of resolution change?
A. 0.43 B. 0.65 C. 2.0 D. 2.3
It is a well-known physiological phenomenon that some materials feel cooler to the touch than others. This is important in the design of instruments for the use of operators, especially in a space station. Experiments conducted at NASA have shown that different materials, e.g., aluminum and plastic, though in identical size and temperature feel very different to the touch. Consider two plates, one made of aluminum and the other of plastic, each at an initial temperature of 25°C. Determine which of the two will feel hotter to the touch of your finger if it is initially at 32°C. Assume that your finger has a density of 1000 kg/m3, specific heat of 4180 J/(kg K), and thermal conductivity of 0.625 W/(m K). Also, properties of aluminum are given in, and plastic is considered to have a
density of 1990 kg/m3, specific heat of 1470 J/(kg K), and thermal conductivity of 0.21 W/(m K).
GIVEN
FIND
which of the aluminum or plastic feel hotter to touch to your finger.
ASSUMPTIONS
constant thermal properties
Negligible contact resistance
The finger and plate behave as semi infinite solid.
SKETCH
Which of the following polyatomic ions has a single minus charge?
a. Acetate b. Sulfate c. Phosphate d. Ammonium