Light

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MCAT Physical › Light

Questions 1 - 10
1

An incandescent light bulb is shown through a glass prism. The certain wavelength of the light is then directed into a glass cuvette containing an unknown concentration of protein. Commonly, this process is called spectroscopy and is used to determine the concentrations of DNA, RNA, and proteins in solutions. The indices of reflection of air, glass, and the solution are 1, 1.5, and 1.3, respectively.

What type of light is produced by the incandescent light bulb?

Visible

IR

Ultraviolet

Gamma

Explanation

Incandescent light bulbs produce visible light of all wavelengths. The mix of red, orange, yellow, green, blue, indigo, and violet (ROYGBIV) give the light its characteristic white appearance. For the MCAT, it is important to know the relative wavelengths of light for the visible spectrum (390 – 700nm) and where visiable wavelengths fit into the overall spectrum of electromagnetic radiation. From longest wavelength to shortest, the sequence of wavelengths is listed below.

Radio > Microwaves > Infrared > Visible > Ultraviolet > X-Rays > Gamma Rays

2

Unpolarized light passes through three polarizing filters. The angle between the first and second filters is 45o. The angle between the second and third filters is also 45o. What is the relationship between the intensity of light emerging from the third filter, , and the incident intensity, ?

No light passes through the third filter

Explanation

Going through the first filter, the intensity of initially unpolarized light decreases by 1/2, so . For each filter after the first, the intensity decreases by an additional factor of , where is the angle between adjacent polarizers. So, after the second filter, we have can see that . Similarly, after the third filter, we have .

3

Unpolarized light passes through three polarizing filters. The angle between the first and second filters is 45o. The angle between the second and third filters is also 45o. What is the relationship between the intensity of light emerging from the third filter, , and the incident intensity, ?

No light passes through the third filter

Explanation

Going through the first filter, the intensity of initially unpolarized light decreases by 1/2, so . For each filter after the first, the intensity decreases by an additional factor of , where is the angle between adjacent polarizers. So, after the second filter, we have can see that . Similarly, after the third filter, we have .

4

An incandescent light bulb is shown through a glass prism. The certain wavelength of the light is then directed into a glass cuvette containing an unknown concentration of protein. Commonly, this process is called spectroscopy and is used to determine the concentrations of DNA, RNA, and proteins in solutions. The indices of reflection of air, glass, and the solution are 1, 1.5, and 1.3, respectively.

What type of light is produced by the incandescent light bulb?

Visible

IR

Ultraviolet

Gamma

Explanation

Incandescent light bulbs produce visible light of all wavelengths. The mix of red, orange, yellow, green, blue, indigo, and violet (ROYGBIV) give the light its characteristic white appearance. For the MCAT, it is important to know the relative wavelengths of light for the visible spectrum (390 – 700nm) and where visiable wavelengths fit into the overall spectrum of electromagnetic radiation. From longest wavelength to shortest, the sequence of wavelengths is listed below.

Radio > Microwaves > Infrared > Visible > Ultraviolet > X-Rays > Gamma Rays

5

Which of the following electron transitions in a hydrogen atom would emit a photon of the lowest frequency?

Explanation

A photon is emitted if the electron goes from a higher to lower energy level, so we need a choice where the energy level, n, decreases. Also, we need to look for the transition that has the smallest energy difference, since frequency is proportional to energy (f = E/h, where h is Planck's constant). Higher energy levels are closer together, so the highest pair of levels has the smallest difference in energy and the lowest frequency of emitted photons.

6

An incandescent light bulb is shown through a glass prism. The certain wavlength of the light is then directed into a glass cuvette containing an unknown concentration of protein. Commonly, this process is called spectroscopy and is used to determine the concentrations of DNA, RNA, and proteins in solutions. The indices of reflection of air, glass, and the solution are 1, 1.5, and 1.3, respectively.

Light is a __________.

particle and a wave

particle

wave

particle or wave, depending on wavelength

Explanation

As Einstein determined, light has properties of both a particle and a wave. In the particle sense, it has mass, velocity, and momentum. The wave property of light allows for diffraction, and constructive and destructive interference. For the MCAT, it is important to know that the photon (the particle of light) has both particle and wave properties. In fact, all objects have both particle and wave properties; however, their wave property becomes less obvious with increasing mass.

7

Which of the following electron transitions in a hydrogen atom would emit a photon of the lowest frequency?

Explanation

A photon is emitted if the electron goes from a higher to lower energy level, so we need a choice where the energy level, n, decreases. Also, we need to look for the transition that has the smallest energy difference, since frequency is proportional to energy (f = E/h, where h is Planck's constant). Higher energy levels are closer together, so the highest pair of levels has the smallest difference in energy and the lowest frequency of emitted photons.

8

Which of the following waves carry the greatest amount of energy?

Gamma rays

Radio waves

Infrared waves

Ultraviolet light

X-rays

Explanation

The energy of a wave increases with increasing frequency and decreasing wavelength. Considering these different waves, radiowaves possess the longest wavelengths and gamma rays the shortest wavelength, thus gamma rays carry the greatest amount of energy.

9

Which of the following waves carry the greatest amount of energy?

Gamma rays

Radio waves

Infrared waves

Ultraviolet light

X-rays

Explanation

The energy of a wave increases with increasing frequency and decreasing wavelength. Considering these different waves, radiowaves possess the longest wavelengths and gamma rays the shortest wavelength, thus gamma rays carry the greatest amount of energy.

10

An incandescent light bulb is shown through a glass prism. The certain wavlength of the light is then directed into a glass cuvette containing an unknown concentration of protein. Commonly, this process is called spectroscopy and is used to determine the concentrations of DNA, RNA, and proteins in solutions. The indices of reflection of air, glass, and the solution are 1, 1.5, and 1.3, respectively.

Light is a __________.

particle and a wave

particle

wave

particle or wave, depending on wavelength

Explanation

As Einstein determined, light has properties of both a particle and a wave. In the particle sense, it has mass, velocity, and momentum. The wave property of light allows for diffraction, and constructive and destructive interference. For the MCAT, it is important to know that the photon (the particle of light) has both particle and wave properties. In fact, all objects have both particle and wave properties; however, their wave property becomes less obvious with increasing mass.

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