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Test Prep MCAT Test Exam
Medical College Admission Test: Verbal Reasoning, Biological Sciences, Physical Sciences, Writing Sample (Page 10 )

Updated On: 12-Jan-2026
Page 10 of 164
PDF with 811 Questions

A continuous spectrum of light, sometimes called blackbody radiation, is emitted from a region of the Sun called the photosphere. Although the continuous spectrum contains light of all wavelengths, the intensity of the emitted light is much greater at some wavelengths than at others. The relationship between the most intense wavelength of blackbody radiation and the temperature of the emitting body is given by Wien's law, = 2.9 × 106 / T, where is the wavelength in nanometers and T is the temperature in kelvins.

As the blackbody radiation from the Sun passes through the cooler gases in the Sun's atmosphere, some of the photons are absorbed by the atoms in these gases. A photon will be absorbed if it has just enough energy to excite an electron from a lower energy state to a higher one. The absorbed photon will have an energy equal to the energy difference between these two states. The energy of a photon is given by E = hf = hc/ where h = 6.63 × 10-34 J·s, Planck's constant, and c = 3 × 108 m/s, the speed of light in a vacuum.
The Sun is composed primarily of hydrogen. Electron transitions in the hydrogen atom from energy state n = 2 to higher energy states are listed below along with the energy of the absorbed photon:

At the center of the visible spectrum is light with a wavelength of 550 nm. What is the frequency of this light?

  1. 9.0 × 108 Hz
  2. 1.8 × 1012 Hz
  3. 5.4 × 1014 Hz
  4. 1.8 × 1016 Hz

Answer(s): C

Explanation:

This question asks for the frequency f of light given its wavelength . If you didn't remember the relationship between the two, you could have figured it out from the formula hf = hc/ given in the passage. Dividing both sides by h, we obtain f = c/, where c is the speed of light in a vacuum. Plugging in = 550 nm, we obtain

which most closely corresponds to choice C.



A continuous spectrum of light, sometimes called blackbody radiation, is emitted from a region of the Sun called the photosphere. Although the continuous spectrum contains light of all wavelengths, the intensity of the emitted light is much greater at some wavelengths than at others. The relationship between the most intense wavelength of blackbody radiation and the temperature of the emitting body is given by Wien's law, = 2.9 × 106 / T, where is the wavelength in nanometers and T is the temperature in kelvins.
As the blackbody radiation from the Sun passes through the cooler gases in the Sun's atmosphere, some of the photons are absorbed by the atoms in these gases. A photon will be absorbed if it has just enough energy to excite an electron from a lower energy state to a higher one. The absorbed photon will have an energy equal to the energy difference between these two states. The energy of a photon is given by E = hf = hc/ where h = 6.63 × 10-34 J·s, Planck's constant, and c = 3 × 108 m/s, the speed of light in a vacuum.
The Sun is composed primarily of hydrogen. Electron transitions in the hydrogen atom from energy state n = 2 to higher energy states are listed below along with the energy of the absorbed photon:

If a star suddenly doubles in size but remains at the same temperature, how does its continuous spectrum change?

  1. The peak intensity occurs at the same wave-length.
  2. The peak intensity occurs at a longer wave-length.
  3. The peak intensity occurs at a shorter wave-length.
  4. The intensity peak narrows.

Answer(s): A

Explanation:

This question asks you to apply Wien's law to the case of a star changing its size and temperature. Wien's law, = 2.9 × 106/ T, indicates that the wavelength of the peak intensity only depends on temperature. Therefore, if the star's temperature doesn't change when it doubles in size, the wavelength of the peak intensity of the star's radiation will not change. Choice A is therefore the correct answer, and choices B and C are wrong. Since the shape of the spectrum, like the location of the peak, is also a function of temperature choice D is wrong as well.



The lead-acid battery, also called a lead storage battery, is the battery of choice for starting automobiles. It contains 6 cells connected in series, each composed of a lead oxide cathode "sandwiched" between 2 lead anodes. Insulating separators are placed between the electrodes to prevent internal short-circuits. Aqueous sulfuric acid is the electrolyte.
When the battery is being discharged, the following reaction takes place:
Pb(s) + PbO2(s) + 2H2SO4 (aq) 2PbSO4 (s) + 2H2O
Reaction 1
The electrode reactions, both written as reductions, are shown in Table 1.
Table 1

As a car operates, the battery is recharged by electricity produced by the car's alternator, an AC generator whose ultimate power source is the car's internal combustion engine. In spite of this, batteries eventually lose

their power. The battery is said to be "dead" when Reaction 1 has proceeded completely to the right.
How many cells would be required to produce a 20-volt lead-acid battery of the type described in the passage?

  1. 5
  2. 10
  3. 15
  4. 20

Answer(s): B

Explanation:

When the half-reactions are written as reductions ­ as they are here ­ the cell voltage is determined by the equation
Ecell = Ecathode - Eanode
(Remember that Ecell must be greater than zero for the reaction to be spontaneous.) The cell voltage is therefore 2.05 V: 1.69 V - (-0.36 V) = 2.05 V
Since the potentials of cells connected in series are additive, a 20 V battery needs ten 2.05 V cells. Choice B is the correct answer. Choice A is a 10 V battery, choice C is a 30 V battery, and choice D is a 40 V battery.



The lead-acid battery, also called a lead storage battery, is the battery of choice for starting automobiles. It contains 6 cells connected in series, each composed of a lead oxide cathode "sandwiched" between 2 lead anodes. Insulating separators are placed between the electrodes to prevent internal short-circuits. Aqueous sulfuric acid is the electrolyte.
When the battery is being discharged, the following reaction takes place:
Pb(s) + PbO2(s) + 2H2SO4 (aq) 2PbSO4 (s) + 2H2O
Reaction 1
The electrode reactions, both written as reductions, are shown in Table 1.
Table 1

As a car operates, the battery is recharged by electricity produced by the car's alternator, an AC generator whose ultimate power source is the car's internal combustion engine. In spite of this, batteries eventually lose their power. The battery is said to be "dead" when Reaction 1 has proceeded completely to the right.
Which reaction takes place at the anode as the battery is discharging?

  1. The first half-reaction, proceeding to the left
  2. The first half-reaction, proceeding to the right
  3. The second half-reaction, proceeding to the left
  4. The second half-reaction, proceeding to the right

Answer(s): C

Explanation:

Oxidation ­ the loss of electrons ­ occurs at the anode. When both half-reactions are written as reductions, the following equation is used to determine the cell potential:
Ecell = Ecathode - Eanode
(Remember that Ecell must be greater than zero for the reaction to be spontaneous.) The cell potential is positive when the reduction potential of the second reaction in Table 1 is subtracted from the first reaction, making the first reaction the cathode and the second reaction the anode. Since oxidation occurs at the anode, the reaction must proceed to the left, making choice C the correct answer. Choice A and choice B are wrong because the first reaction is the cathode reaction, not the anode reaction. Choice D is wrong because the second reaction proceeds to the left, not to the right.



The lead-acid battery, also called a lead storage battery, is the battery of choice for starting automobiles. It contains 6 cells connected in series, each composed of a lead oxide cathode "sandwiched" between 2 lead anodes. Insulating separators are placed between the electrodes to prevent internal short-circuits. Aqueous sulfuric acid is the electrolyte.
When the battery is being discharged, the following reaction takes place:
Pb(s) + PbO2(s) + 2H2SO4 (aq) 2PbSO4 (s) + 2H2O
Reaction 1
The electrode reactions, both written as reductions, are shown in Table 1.
Table 1

As a car operates, the battery is recharged by electricity produced by the car's alternator, an AC generator whose ultimate power source is the car's internal combustion engine. In spite of this, batteries eventually lose their power. The battery is said to be "dead" when Reaction 1 has proceeded completely to the right.
Where does oxidation occur in the lead storage battery?

  1. At the lead oxide cathodes
  2. At the lead oxide anodes
  3. At the lead cathodes
  4. At the lead anodes

Answer(s): D

Explanation:

Oxidation occurs when a species' oxidation number increases; reduction occurs when a species' oxidation number decreases. Also discussed earlier, oxidation occurs at the anode and reduction occurs at the cathode.
From the answer choices, it can be seen that lead oxide and lead are the only species that have to be investigated. In Reaction 1, Pb4+, in lead oxide, is going to Pb2+, in lead sulfate. Since lead's oxidation number has decreased, it has been reduced. Choice A, choice B, and choice C can, therefore, all be eliminated, leaving choice D as the correct answer. Choice D is correct because lead is being reduced at the anode ­ where oxidation occurs ­ from Pb to Pb2+.



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