In the scientific method, natural selection is classified as a
A) theory
B) hypothesis
C) model
D) principle
A
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Most of the mass of the Milky Way seems to exist in the form of
A) population II stars in the Halo. B) dark matter out in the Halo. C) population I stars in the disk. D) hydrogen gas in the disk and spiral arms. E) the black hole in the Galactic Center.
Of the many different features of the scientific method, one feature is the most important. Without it, we should not call a field a "science." This feature is
A) the use of only those theories that are known, for certain, to be true. B) that the results should lead to some useful technological application [for example, a useful medical treatment]. C) the use of quantitative measurements. D) the use of mathematics. E) the interaction between theory and observation.
An electron is moving at a speed of 4.8 × 10^6 m/s at an angle of 30.0° with respect to a uniform magnetic field of 9.2 × 10^–4 T. What is the radius of the resulting helical path? (me = 9.11 × 10^–31 kg, qe = 1.60 × 10^–19 C)
a. 2.6 cm b. 3.8 cm c. 5.5 cm d. 1.5 cm e. 2.9 cm
Sodium metal is paramagnetic with a dimensionless magnetic susceptibility (?) of 8.48×10-6 . The paramagnetism of sodium metal is due to the rotation of some of the spins of the metal’s free electrons into the direction of the applied magnetic field. The applied magnetic field is equal to 1×105 A/m. Sodium metal is BCC with a lattice parameter of 0.428×10-9 m, and sodium is from Group 1A of the periodic table.
(a) What is the intensity of magnetization or the dipole moment per unit volume? (b) For sodium, what is the number of atoms per unit volume, and what is the number of free electrons per unit volume? (c) What is the dipole moment per sodium atom? (d) Assuming that all of the magnetic susceptibility is due to the orientation of free electron spins, what is the net number of free electron spins per atom oriented in the direction of the applied magnetic field?