Medical Tests MCAT-TEST Exam Questions & Answers

When light in the ultraviolet region of the spectrum is shone on a type of material known as a phosphor, it fluoresces and emits light in the visible region of the spectrum. Lamps that utilize this property, known as fluorescent lamps, are very efficient light sources. The arrangement of a typical fluorescent lamp is shown below. The lamp is a glass tube whose inside walls are covered with a phosphor. The tube has an appreciable length-to-diameter ratio so as to reduce the power losses at each end, and it is filled with argon gas mixed with mercury vapor. Inside each end of the tube are tungsten electrodes covered with an emission material.

Electrons are liberated at the cathode and accelerated by an applied electric field. These free electrons encounter the gas mixture, ionizing some mercury atoms and exciting others. Since it requires more energy to ionize the atoms than to excite the electrons, more excitation than ionization occurs. When the excited electrons revert to their ground state, they radiate ultraviolet photons with a wavelength of 253.7 nm. These photons impinge on the phosphor coating of the tube and excite electrons in the phosphor to higher energy states. The excited electrons in the phosphor return to their ground state in two or more steps, producing radiation in the visible region of the spectrum. Not every fluorescent lamp emits the same color of radiation; the color is dependent on the relative percentages of different heavy metal compounds in the phosphor.

The fluorescent lamp shown operates at 100 volts and draws 400 milliamps of current during normal operation. Of the total power that the lamp consumes, only 25% is converted to light, while the remaining 75% is dissipated as heat. This energy keeps the lamp at its optimum working temperature of 40°C. In the lamp shown, the phosphor coating is calcium metasilicate, which emits orange to yellow light.

Some fluorescent light bulbs are observed to glow for a short period after their power supply has been turned off. This glow is generated mainly by:

A. the incandescence of the hot ionic gas within the bulb surface.

B. emission of light stored as vibrational kinetic energy in the phosphor coating.

C. the dissipation of electric charge built up on the bulb's surface.

D. electrons returning to the ground state from excited states after the power was shut off.

Arsenic is widely distributed in sulfide ores of many metals and is obtained as a byproduct of copper smelting. The element, as well as many compounds of arsenic -- for example arsine, AsH3 -- are extremely poisonous. Arsenic compounds, as might be expected, have found use in herbicides and pesticides, but have also been successful in some pharmacological agents. The first useful antisyphilitic agent, Salvarsan, or 3,3'-diamino-4,4'-dihydroxyarsenobenzene dihydrochloride, is an arsenic compound. The element sublimes at 600°C, forming tetrahedral molecules, As4. Arsenic is a metalloid, possessing properties characteristic of both metals and non-metals. Arsenic is a gray-colored, metalliclooking solid, but arsenic vapor is yellow in color, has a garlic-like odor, and is very poisonous. If the arsenic vapor is cooled rapidly, an unstable, yellow crystalline allotrope consisting of As4 molecules is produced. The Marsh test, based on the instability of arsine, is a very sensitive test for the presence of arsenic. This test is commonly employed in the detection of arsenic poisoning--either before or after death. The apparatus for the Marsh test is shown in Figure 1.

Figure 1

Typically, a sample, usually hair, is taken from a person suspected of being the victim of arsenic poisoning. This sample is then treated in such a way so as to produce arsenic oxide, As4O6. The oxide is then placed into the apparatus shown

in Figure 1 and reacted according to Reaction 1.

As4O6 + 12Zn(s) + 24H+(aq) AsH3(g) + 12Zn2 +(aq) + 6H2O

Reaction 1

When the evolved arsine is ignited it decomposes into its elements. The arsenic vapor is rapidly cooled when it encounters the porcelain evaporating dish and deposits a black mirror of arsenic on the bottom, indicating the presence of arsenic

in the original sample.

The phase diagram for arsenic is shown below. At what point does liquid arsenic exist?

A. 1.0 bar and 874 K

B. 1.0 bar and 1673 K

C. 223 bar and 1672 K

D. 223 bar and 873 K

Family violence, such as domestic violence, child abuse, and elder abuse, are serious and pervasive problems in the United States. On an annual basis, the National Crime Survey has found domestic violence results in 21000 hospitalizations, 99800 days of hospitalization, 28700 emergency department visits, and 39900 visits to physicians.

Currently there is little consensus about the definitions of intimate violence. Even the terms employed are varied; for example, domestic violence, conjugal violence, intimate abuse, and partner abuse. Similarly, there are a range of causal explanations, and these are contingent upon the theoretical perspective employed. There is also controversy whether the term "violence," "abuse," or "aggression" should be used. Finally, within the terms adopted, there is no consensus about the victim-perpetrator relationship. For example, do the terms refer to a married co-habiting couple? Two heterosexual individuals who do not reside together but are dating? All this has implications for research, practice, and policy.

The National Violence Against Women Survey was one of the largest studies sponsored by the National Institute of Justice and the Centers for Disease Control and Prevention. It systematically analyzed crime against women in the United States. A total of 8000 men and 8000 women in the United States were interviewed on the phone using a closed-ended survey. Table 1 displays the breakdown of figures when examining life time victimization by racial groups.

Table 1 Percentage of people victimized by an intimate partner in lifetime, by victim gender, type of victimization, and victim race Source: Adapted from P Tjaden and N. Thoennes, "Consequences of Intimate Partner Violence: Findings from the National Violence Against Women Survey."

When interpreting the data about lifetime prevalence rates of physical assault, as experienced by women in the four different racial minority groups, which of the following sociological theories is least helpful at explaining found differences?

A. Attribution theory

B. Feminist theory

C. Social desirability theory

D. Conflict theory