Compound Microscope: You have a choice between two lenses of focal lengths fa and fb, where fb = 2fa, to use as the objective lens in building a compound microscope. If the magnification you obtain using lens a is Ma, what will be the magnification when using lens b?
A. Mb = 2 Ma
B. Mb = 4 Ma
C. Mb = 8 Ma
D. Mb = Ma/4
E. Mb = Ma/2
Answer: E
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Arcturus has an mV = –0.04 and MV = –0.3 . Its distance is 10^–3.4 pc
a. True b. False Indicate whether the statement is true or false
Estimate (a) the heat transfer coefficient for a spherical fuel droplet injected into a diesel engine at 80°C and 90 m/s. The oil droplet is 0.025 mm in diameter, the cylinder pressure is 4800 kPa, and the gas temperature is 944 K. (b) Estimate the time required to heat the droplet to its self-ignition temperature of 600°C.
GIVEN
• An oil droplet injected into a diesel engine
• Initial droplet temperature (To) = 80°C
• Injection velocity (Ud) = 90 m/s
• Droplet diameter (D) = 0.025 mm = 2.5 × 10–5 m
• Cylinder pressure = 4800 kPa
• Gas temperature (T?) = 944 K = 671°C FIND (a) The heat transfer coefficient ( h c) (b) The time (t) required for the drop to reach 300°C ASSUMPTIONS
• Radiative heat transfer is negligible
• The gas has the properties of air and behaves as an ideal gas
• Only the density of the gas is affected by pressure
• Variation of the thermal conductivity of the oil with temperature is negligible
• Fuel has the same properties as unused engine oil
SKETCH
Most stars in the Milky Way probably formed:
A) alone. B) in intergalactic space, then were swept up into the Galaxy. C) in clusters in the Galaxy's spiral arms. D) from planetary nebulae. E) in the galactic Nucleus, then migrated outward later.
For a specific element, photons of how many different energies could be absorbed by electrons to jump from the n = 1 to n = 5 level?
a. 20 b. 10 c. 6 d. 1 e. 4