MCAT Physical : Electromagnetic Spectrum

Study concepts, example questions & explanations for MCAT Physical

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Example Questions

Example Question #1 : Electromagnetic Spectrum

You observe several stars in the distance with varying colors. Which of the following stars would have the highest surface temperature?

Possible Answers:

Blue

Yellow

Red

Violet

Correct answer:

Violet

Explanation:

The light portion of the electromagnetic spectrum, from lowest to highest frequency, is red, orange, yellow, green, blue, indigo, violet (ROYGBIV).

Frequency is proportional to temperature, and wavelength is inversely proportional to frequency. Since the energy level corresponds with the temperature, objects that emit a higher frequency and shorter wavelength photon will have higher energy. This corresponds with violet, as it is the highest frequency (shortest wavelength) of visible light

Example Question #2 : Electromagnetic Spectrum

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.

The prism is designed to select for the color of visible light that has the longest wavelength. What color is this, and what are the expected wavelength ranges?

Possible Answers:

Blue; 600nm

Green; 500nm

Red; 700nm

Orange; 600nm

Correct answer:

Red; 700nm

Explanation:

We know that the visible spectrum has wavelengths of 390nm to 700nm. The wavelengths of light around the 700nm range are red.

Using the ROYGBIV acronym, we know that red has the longest wavelength and violet the shortest. While this may seen to be a difficult question asking for the wavelengths of light that correspond to certain colors, this is helpful on the MCAT for estimating answers and may be worth the time learning. The expected range of wavelengths for the red portion of the visible spectrum is 650nm to 700 nm. Keep in mind that, because it has the longest wavelength, red light will also have the lowest frequency.

Example Question #3 : Electromagnetic Spectrum

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?

Possible Answers:

Gamma

IR

Visible

Ultraviolet

Correct answer:

Visible

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

Example Question #4 : Electromagnetic Spectrum

Which color of the visible spectrum of light has the highest energy of the answer choices?

Possible Answers:

Green

Orange

Yellow

Red

Blue

Correct answer:

Blue

Explanation:

The highest energy of any visible light belongs to violet. The greater the wavelength, the lower the energy of the light. The greater the frequency, the higher the energy of the light. This is why ultraviolet light ("ultra" meaning "beyond" violet) is so damaging to DNA. Out of the answer choices, blue light has the lowest wavelength and greatest frequency, making it the highest energy.

Example Question #5 : Electromagnetic Spectrum

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

Possible Answers:

X-rays

Radio waves

Gamma rays

Ultraviolet light

Infrared waves

Correct answer:

Gamma 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.

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