Question 1

Ink jet printers produce high resolution output, at a lower cost than laser printers, by generating charged ink

droplets which are then deflected onto a sheet of paper by an electric field. Each droplet deflected by the field

strikes the paper and forms a tiny dot of ink. While a typical printed letter requires about 100 drops, an ink jet

printer is able to produce drops at a rate of 100,000 per second.

The essential elements of the ink jet printer head are shown in Figure 1. The drop generator produces the ink

droplets, each with a mass of approximately 1.2 × 10−10 kg and a diameter of approximately 30 μm. The drops

then enter a highly precise charging unit which controls the charge q on each droplet to within 2%, with typical

charges for drops generated by various ink jet printers ranging from −1.0 × 10−13 C to −3.0 × 10−14 C. The

charged droplets are subsequently passed through the deflecting plates between which a variable electric field

is generated. The electronically controlled electric field between the plates is typically varied over a range from

1.0 × 106 N/C to 5.4 × 106 N/C, and is used to aim the ink droplet at the paper.

An ink jet printer deflects a particular ink droplet by 1.5 mm in the region of the deflector. Which of the following

is a possible value of the work done on the droplet?

Section: Physical Sciences

Options :

A : No work

B :

C :

D :

Answer: C

Question 2

Electromagnetic radiation from space constantly bombards the earth. Most wavelengths are absorbed by the

atmosphere; however, there are two “windows” of nonabsorption through which significant amounts of radiation

reach the ground. The first transmits ultraviolet and visible light, as well as infrared light or heat; the second

transmits radio waves. As a result, terrestrial organisms have evolved a number of pigments that interact with

light in various ways: some capture light energy, some provide protection from light-induced damage, and some

serve camouflage or signaling purposes.

Among these compounds are many conjugated polyenes, which play important roles as photoreceptors. For

every chemical compound, there are certain wavelengths of light whose quanta possess exactly the correct

amount of energy to raise electrons from their ground state to higher-energy orbitals. For most organic

compounds, these wavelengths are in the UV range. However, conjugated double bond systems stabilize the

electrons, so that they can be excited by lower-frequency photons with wavelengths in the visible spectrum.

Such a pigment, known as a chromophore, will then transmit the “subtraction color,” a color complementary to

the one absorbed. For instance, carotene, a hydrocarbon compound with eleven conjugated double bonds,

absorbs blue light and transmits orange. The wavelength that is absorbed generally increases with the number

of conjugated bonds; rings and side-chains also affect wavelength.

Among the many biological molecules that are affected by light is DNA, the genetic material of living organisms.

DNA absorbs ultraviolet light, and may be damaged by UVC (< 280 nm) and UVB (280-315 nm). UVA (315-400

nm) and visible light can actually repair light-induced damage to DNA by a process called photorepair. For this

reason, UVA, which also stimulates tanning, was once considered beneficial. However, there is now increasing

evidence that UVA can damage skin.

The color-producing quality of conjugated polyenes is attributable to:

Section: Biological Sciences

Options :

A : antibonding orbitals.

B : resonance.

C : polarity.

D : optical activity

Answer: B

Question 3

Several techniques have been developed to determine the order of a reaction. The rate of a reaction cannot be

predicted on the basis of the overall equation, but can be predicted on the basis of the rate-determining step.

For instance, the following reaction can be broken down into three steps.

A + D → F + G

Step 1

A → B + C

(slow)

Step 2

B + D → E + F

(fast)

Step 3

E + C → G

(fast)

Reaction 1

In this case, the first step in the reaction pathway is the rate-determining step. Therefore, the overall rate of the

reaction must equal the rate of the first step, k1 [A] where k1 is the rate constant for the first step. (Rate

constants of the different steps are denoted by kx

, where x is the step number.)

In some cases, it is desirable to measure the rate of a reaction in relation to only one species. In a secondorder reaction, for instance, a large excess of one species is included in the reaction vessel. Since a relatively

small amount of this large concentration is reacted, we assume that the concentration essentially remains

unchanged. Such a reaction is called a pseudo first-order reaction. A new rate constant, k', is established, equal

to the product of the rate constant of the original reaction, k, and the concentration of the species in excess.

This approach is often used to analyze enzyme activity.

In some cases, the reaction rate may be dependent on the concentration of a short-lived intermediate. This can

happen if the rate-determining step is not the first step. In this case, the concentration of the intermediate must

be derived from the equilibrium constant of the preceding step. For redox reactions, the equilibrium can be

correlated with the voltage produced by two half-cells by means of the Nernst equation. This equation states

that at any given moment:

Equation 1

When

a A + b B → c C + d D

Reaction 2

Note: R = 8.314 J/K·mol; F = 9.6485 × 104 C/mol.)

Catalysts are effective in increasing the rate of a reaction because they:

Section: Physical Sciences

Options :

A : increase the energy of the activated complex

B :

increase the value of the equilibrium constant.

C :

decrease the number of collisions between reactant molecules.

D : lower the activation energy

Answer: D

Question 4

The Russian wheat aphid, Diuraphis noxia, is a small green insect discovered in southern Russia around the

turn of the century. Agricultural researchers are not quite sure, but they believe the Russian aphid adapted itself

to wheat about ten thousand years ago, when the crop was first domesticated by man. What is not in doubt is

the insect’s destructiveness. Spread by both wind and human transport, the Russian aphid has destroyed

wheat fields throughout Asia, Africa, and Latin America. Until a few years ago, the United States had been free

of this pest. But in the spring of 1986, a swarm of Russian aphids crossed the Mexican border and settled a few

hundred miles north, in central Texas. From there, it quickly spread to other Western states, destroying wheat

fields all along its path. In fact, the level of destruction has been so great over the past five years that

entomologists are calling the Russian aphid the greatest threat to American agriculture since the Hessian fly,

Phytophaga destructor, was inadvertently brought to the colonies on ships by German mercenary troops during

the Revolutionary War. A combination of several factors have made it particularly difficult to deal with the threat

posed by this aphid. First, Russian aphids reproduce asexually at a phenomenal rate. This process, known as

parthenogenesis, often results in as many as twenty generations of insects in a single year. Although most

generations remain in a limited geographic area because they have no wings, a few generations are born with

wings, allowing the insect to spread to new areas. Second, because wheat is a crop with a very low profit

margin, most American farmers do not spray it with pesticides; it simply is not economical to do so. And since

the Russian aphid has only recently entered the United States, it has no natural enemies among North

American insects or animals. As a result, there have been no man-made or natural obstacles to the spread of

the Russian aphid in the United States.

Agricultural researchers seeking to control the Russian aphid have looked to its place of origin for answers. In

the Soviet Union, the Russian aphid has been kept in check by predators which have evolved alongside it over

many thousands of years. One species of wasp seems to be particularly efficient at destroying the aphid. The

pregnant females of the species search the Russian aphid’s home, the interior of a wheat stalk, sting the aphid

into paralysis, and then inject an egg into its body. When the egg hatches the wasp larva feeds off of the aphid,

killing it in the process.

The introduction of predators like the wasp, coupled with the breeding of new strains of insect-resistant wheat,

may substantially curb the destructiveness of the Russian aphid in the future. For the time being, however,

American farmers are left to their own devices when it comes to protecting their wheat crops.

Which of the following statements would be most in agreement with the statements in the passage?

Section: Verbal Reasoning

Options :

A : It is no longer economical to grow crops with low profit margins.

B : Humans are powerless against the forces of nature.

C : Regional ecosystems are often severely damaged when new organisms are introduced.

D :

It is more difficult to stop the spread of an insect that reproduces asexually than one that reproduces

sexually.

Answer: C

Question 5

The nuclei of certain unstable isotopes will spontaneously decay, producing a more stable nucleus and

releasing a particle or quantity of energy. Alpha decay releases a helium nucleus, beta decay emits an electron,

while gamma decay is the emission of a high energy photon. Each type of radioactive decay is characterized, in

part, by the half-life of the radioactive material – the time required for half of the nuclei in a sample to undergo

decay. Examples of such decays are shown in Figure 1.

Figure 1

A Geiger counter can be used to detect the decay of radioactive materials. A simple Geiger counter consists of

a hollow metal cylinder with a wire along its axis. The cylinder is filled with low pressure argon gas and a high

voltage difference is applied between the wire and the cylinder. When alpha, beta, or gamma radiation passes

through the cylinder, it interacts with the gas particles and leads to the formation of ions which cause a

discharge between the wire and the cylinder. The consequent current may be used to drive a speaker,

producing the characteristic clicking sound of the Geiger counter each time a pulse of current occurs. The

Geiger counter circuitry is shown in Figure 2.

Figure 2

A Geiger counter is best suited for which of the following applications:

Section: Physical Sciences

Options :

A :

comparing the relative magnitudes of radioactivities of two nuclear waste depositories.

B : spatially locating a radioactive isotope injected into a patient.

C :

calculating the total energy of a radioactive particle.

D : determining the identity of various types of radioactivity.

Answer: A

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