Choose the correct statements concerning spectral classes of stars. (Give ALL correct answers, i.e., B, AC, BCD...)
A) K-stars are dominated by lines from ionized helium because they are so hot.
B) Neutral hydrogen lines dominate the spectrum for stars with temperatures around 10,000 K because a lot of the hydrogen is in the n=2 level.
C) The spectral sequence has recently been expanded to include L, T, and Y classes.
D) The spectral types of stars arise primarily as a result of differences in temperature.
E) Oh Be A Fine Guy/Girl Kiss Me, is a mnemonic for remembering spectral classes.
F) Hydrogen lines are weak in type O-stars because most of it is completely ionized.

Answers

Answer 1

The correct statements concerning spectral classes of stars are B, C, D, F.

A) This statement is incorrect because K-stars are cooler stars and are not hot enough to be dominated by ionized helium lines.

B) This statement is correct. When the temperature of a star is around 10,000 K, most of the hydrogen atoms are in the second energy level (n=2), which leads to the formation of strong neutral hydrogen lines.

C) This statement is correct. The original spectral sequence (OBAFGKM) has been expanded to include additional classes such as L, T, and Y, which are used to classify cooler and less massive stars.

D) This statement is correct. The spectral types of stars are primarily based on temperature, which influences the ionization state and the strength of spectral lines in the star's spectrum.

E) This statement is a mnemonic used to remember the spectral sequence but is not a statement concerning spectral classes of stars.

F) This statement is correct. Type O-stars are the hottest and most massive stars, and their surface temperature is high enough to ionize most of the hydrogen atoms, which results in the weakness of hydrogen lines in their spectra.

Hence, B,C,D,F statements are correct which concerning spectral classes of stars .

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Related Questions

Answers

The angular separation of two Sodium lines is calculated as (C) 1.80.

The angular separation between the two Sodium lines can be calculated using the formula:

Δθ = λ/d

Where Δθ is the angular separation, λ is the wavelength difference between the two lines, and d is the distance between the adjacent ruled lines on the diffraction grating.

First, we need to convert the given wavelengths from nanometers to meters:

λ1 = 580.0 nm = 5.80 × 10⁻⁷ m
λ2 = 590.0 nm = 5.90 × 10⁻⁷ m

The wavelength difference is:

Δλ = λ₂ - λ₁ = 5.90 × 10⁻⁷ m - 5.80 × 10⁻⁷ m = 1.0 × 10⁻⁸ m

The distance between adjacent ruled lines on the diffraction grating is given as 300 lines per mm, which can be converted to lines per meter:

d = 300 lines/mm × 1 mm/1000 lines × 1 m/1000 mm = 3 × 10⁻⁴ m/line

Substituting the values into the formula, we get:

Δθ = Δλ/d = (1.0 × 10⁻⁸ m)/(3 × 10⁻⁴ m/line) = 0.033 radians

Finally, we convert the answer to degrees by multiplying by 180/π:

Δθ = 0.033 × 180/π = 1.89 degrees

Rounding off to two significant figures, the answer is:

(C) 1.80

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Consider three identical metal spheres, a, b, and c. sphere a carries a charge of 5q. sphere b carries a charge of -q. sphere c carries no net charge. spheres a and b are touched together and then separated. sphere c is then touched to sphere a and separated from it. lastly, sphere c is touched to sphere b and separated from it.

required:
a. how much charge ends up on sphere c?
b. what is the total charge on the three spheres before they are allowed to touch each other?

Answers

a. Sphere c ends up with a charge of -3q.

b. The total charge on the three spheres before they are allowed to touch each other is 5q - q = 4q.

a. When spheres a and b are touched together and then separated, charge is transferred between them until they reach equilibrium. Since sphere a has a charge of 5q and sphere b has a charge of -q, the total charge transferred is 5q - (-q) = 6q. This charge is shared equally between the two spheres, so sphere a ends up with a charge of 5q - 3q = 2q, and sphere b ends up with a charge of -q + 3q = 2q.

When sphere c is touched to sphere a and separated, they share charge. Sphere a has a charge of 2q, and sphere c has no net charge initially. The charge is shared equally, so both spheres end up with a charge of q.

Similarly, when sphere c is touched to sphere b and separated, they also share charge. Sphere b has a charge of 2q, and sphere c has a charge of q. The charge is shared equally, so both spheres end up with a charge of (2q + q) / 2 = 3q/2.

Therefore, sphere c ends up with a charge of -3q (opposite sign due to excess electrons) and the total charge on the three spheres before they are allowed to touch each other is 5q - q = 4q.

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The net force on any object moving at constant velocity is a. equal to its weight. b. less than its weight. c. 10 meters per second squared. d. zero.

Answers

The net force on any object moving at constant velocity is zero. Option d. is correct .

An object moving at constant velocity has balanced forces acting on it, which means the net force on the object is zero. This is due to Newton's First Law of Motion, which states that an object in motion will remain in motion with the same speed and direction unless acted upon by an unbalanced force. This is due to Newton's first law of motion, also known as the law of inertia, which states that an object at rest or in motion with a constant velocity will remain in that state unless acted upon by an unbalanced force.

When an object is moving at a constant velocity, it means that the object is not accelerating, and therefore there must be no net force acting on it. If there were a net force acting on the object, it would cause it to accelerate or decelerate, changing its velocity.

Therefore, the correct answer is option (d) - the net force on any object moving at a constant velocity is zero.

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