As viewed from Earth, in which zodiac constellation does the Sun appear to be located on April 21?
A) Leo
B) Aquarius
C) Libra
D) Aries
D) Aries
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A photon with energy of 104 eV is in what part of the electromagnetic spectrum?
(a) ?-ray (b) X-ray (c) UV (d) Visible
The half-life of a radioactive element is the time it takes for:
A) half of the radioactive atoms to double themselves. B) half of the radioactive atoms to decay into isotopes. C) the radioactive atoms to increase by half of its initial quantity. D) the radioactive atoms to increase to 1.5 times of its initial quantity.
In order for the atoms in a neon discharge tube (or a neon beer sign) to emit their characteristic orange light, it is necessary that
A) there be no unoccupied energy levels in each atom. B) each atom carry a net electric charge. C) the atoms be continually replaced with fresh atoms, because the energy of the atoms tends to be used up with continued excitation, resulting in dimmer and dimmer light. D) electrons first be given energy to raise them from their ground state to an excited state.
Find the radius of a star image formed on the retina of the eye if the aperture diameter (the pupil) at night is 0.70 cm and the length of the eye is 3.2 cm. Assume the wavelength of starlight in the eye is 500 nm. (1 nm = 10?9 m)
a. 2.8 × 10^?4 m b. 5.6 × 10^?4 m c. 3.1 × 10^?5 m d. 2.8 × 10^?6 m e. 3.2 × 10^?4 m