Explain the three kind of nebulae
What will be an ideal response?
The three kinds of nebulae are emission nebulae, reflection nebulae, and dark nebulae.Emission nebulae are produced when a hot star excites the gas near it to produce an emission spectrum. The star must be hotter than about B1 (25,000 K). Cooler stars do not emit enough ultraviolet radiation to ionize the gas. Emission nebulae have a distinctive pink color produced by the blending of the red, blue, and violet Balmer lines. Emission nebulae are also called H II regions, following the custom of naming gas with a roman numeral to show its state of ionization. H I is neutral hydrogen, and H II is ionized.A reflection nebula is produced when starlight scatters from a dusty nebula. Consequently, the spectrum of a reflection nebula is just the reflected absorption spectrum of starlight. Gas is surely present in a reflection nebula, but it is not excited to emit photons.Dark nebulae are dense clouds of gas and dust that obstruct the view of more distant stars. Some are generally round, but others are twisted and distorted, as shown at the left, suggesting that even when there are no nearby stars to ionize the gas or produce a reflection nebula, there are breezes and currents pushing through the interstellar medium.
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A refrigerator weighing 1500 N is to be lifted onto a truck bed that is 1.0 m above the ground. When pushed up a slanting ramp 2.0 m in length a force of only 750 N is required to move it at constant velocity. Neglecting friction and comparing the work involved in lifting the refrigerator straight up to the work in pushing it along the ramp, there is
A. an equal amount of work is required in each case. B. less work required when the ramp is employed. C. more work required when the ramp is employed.
In a smoke detector, current flows between the plates because the radiation ___________ the air
Fill in the blank(s) with correct word
The ______________ angle is measured between the horizon and the line of sight to the object
a. declination b. altitude c. inclination d. zenith
A simple pendulum has a mass of 0.50 kg and a length of 1.0 m. It is displaced through an angle of 30° and then released. After a time, the maximum angle of swing is only 10°. How much energy has been lost to friction?
a. 2.0 J c. 0.66 J b. 1.6 J d. 0.58 J