Question

Determine which of the following statements are false, and correct them. (a) Electromagnetic radiation is incapable of passing through water. (b) Electromagnetic radiation travels through a vacuum at a constant speed, regardless of wavelength. (c) Infrared light has higher frequencies than visible light. (d) The glow from a fireplace, the energy within a microwave oven, and a foghorn blast are all forms of electromagnetic radiation.

Short answer

False Statements and Corrections: (a) Electromagnetic radiation is capable of passing through water, but the degree to which it can penetrate depends on its wavelength. (c) Infrared light has lower frequencies than visible light. (d) The glow from a fireplace (infrared radiation) and the energy within a microwave oven (microwave radiation) are forms of electromagnetic radiation, but a foghorn blast (sound wave) is not.

Step-by-step solution

Statement (a)

Electromagnetic radiation is incapable of passing through water. Analysis: This statement is false. Electromagnetic radiation can pass through water, but the degree to which it can penetrate depends on its wavelength. For example, radio waves can travel through water relatively easily, whereas visible light is absorbed to a greater extent. Corrected Version: Electromagnetic radiation is capable of passing through water, but the degree to which it can penetrate depends on its wavelength.

Statement (b)

Electromagnetic radiation travels through a vacuum at a constant speed, regardless of wavelength. Analysis: This statement is true. Electromagnetic radiation travels at the speed of light in a vacuum, which is about 299,792 kilometers per second (km/s) or 186,282 miles per second (mi/s). The speed of light in a vacuum is constant, and does not depend on the wavelength or frequency of the radiation.

Statement (c)

Infrared light has higher frequencies than visible light. Analysis: This statement is false. Infrared light has lower frequencies than visible light. The electromagnetic spectrum consists of different types of waves with different wavelengths and frequencies. Infrared light has longer wavelengths and lower frequencies as compared to visible light. Corrected Version: Infrared light has lower frequencies than visible light.

Statement (d)

The glow from a fireplace, the energy within a microwave oven, and a foghorn blast are all forms of electromagnetic radiation. Analysis: This statement is partially true. The glow from a fireplace (infrared radiation) and the energy within a microwave oven (microwave radiation) are both forms of electromagnetic radiation. However, a foghorn blast is a mechanical wave (sound wave), which is not a form of electromagnetic radiation. Corrected Version: The glow from a fireplace (infrared radiation) and the energy within a microwave oven (microwave radiation) are forms of electromagnetic radiation, but a foghorn blast (sound wave) is not.

Key concepts

Properties of Electromagnetic Radiation

Electromagnetic radiation encompasses a range of phenomena, all of which move through space as waves. A core property of these waves is that they can travel through a vacuum—meaning they do not require a medium, unlike sound waves which do. Electromagnetic waves carry energy with them, which can have various effects depending on their wavelength.

One interesting aspect is their ability to pass through different materials, including water. While some forms of electromagnetic radiation, like certain radio waves, penetrate water easily, others, like visible light, get absorbed substantially. This variance is due to the differing wavelengths and frequencies of electromagnetic waves. In general, waves with longer wavelengths can pass through materials better than those with shorter wavelengths.

The behavior of electromagnetic radiation is also characterized by its frequency and amplitude. Frequency refers to the number of wave cycles that pass a certain point per unit time, and is inversely proportional to wavelength. Amplitude, on the other hand, is a measure of the wave's strength or intensity. Together, these properties define how electromagnetic radiation interacts with objects and materials, as well as its potential applications in technologies like telecommunications, medical imaging, and navigation systems.

Speed of Light in a Vacuum

A fundamental constant in physics is the speed at which light travels in a vacuum. Light and all types of electromagnetic radiation travel at approximately 299,792 kilometers per second (km/s), or about 186,282 miles per second (mi/s) in a vacuum. This speed, denoted by the symbol 'c', is invariant—meaning it stays constant regardless of the observer's relative motion or the source of light.

The constant speed of light in a vacuum underpins the theory of relativity and has profound implications for understanding concepts such as spacetime and the causality principle. Its constancy also applies across the entire electromagnetic spectrum; no matter if it's gamma rays or radio waves, the speed of light remains unchanged. This value is used in equations that relate energy to mass (E=mc²) and is fundamental for calculations and concepts across many areas of physics. The constancy of the speed of light for all wavelengths establishes a basis for measuring astronomical distances, timekeeping, and navigating space.

Electromagnetic Spectrum

The electromagnetic (EM) spectrum is a term describing the entire range of electromagnetic radiation. From gamma rays with the shortest wavelengths, down to radio waves with the longest wavelengths, the electromagnetic spectrum is vast and varied. Each portion of the spectrum has unique properties and behaves differently when interacting with matter.

For instance, infrared radiation, situated near the middle of the spectrum, has longer wavelengths than visible light, which we perceive with our eyes, and thus has lower frequencies. This characteristic is one reason why infrared light is often used in heat-sensing applications, such as thermal cameras. On the other hand, ultraviolet light, with higher frequencies than visible light, has enough energy to cause chemical reactions, which is why it can be harmful to skin and is used in sterilizing equipment.

The EM spectrum is fundamental to understanding how various technologies operate. Microwaves, for example, are used to heat food because their particular wavelength is adept at agitating water molecules. Radios and televisions receive signals in the form of radio waves, which have longer wavelengths and can travel long distances. Understanding the EM spectrum not only informs us about the nature of light and energy but also about the diverse range of applications that different types of electromagnetic radiation have in our daily lives.