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Chapter 22: Problem 20

Saint Elmos fire is an eerie glow that appears at the tips of masts and yardarms of sailing ships in stormy weather and at the tips and edges of the wings of aircraft in flight. St. Elmo's fire is an electrical phenomenon. Explain it, concisely.

Short Answer

Expert verified
Answer: Saint Elmo's fire, or corona discharge, is an atmospheric electrical phenomenon characterized by a bluish or greenish glow appearing at the tips of masts and yardarms of sailing ships, and at the tips and edges of the wings of aircraft in flight. It occurs during stormy weather and is caused by the ionization of air molecules due to strong electric fields associated with thunderstorms or high voltage sources. This ionization leads to the formation of a plasma, which emits light, creating the glow of Saint Elmo's fire. Historically, sailors considered it an omen, with some believing it offered protection from Saint Elmo, the patron saint of sailors, while others saw it as a warning of an impending storm or disaster. Its presence during stormy weather provided sailors with a visible indication of potential dangers.

Step by step solution

01

Definition and Occurrence

Saint Elmo's fire, also known as corona discharge, is an atmospheric electrical phenomenon, usually observed during stormy weather and characterized by a bluish or greenish glow appearing at the tips of masts, yardarms of sailing ships and at the tips and edges of the wings of aircraft in flight.
02

Scientific Explanation

It is caused by the ionization of air molecules, resulting from the strong electric fields associated with thunderstorms or other sources of high voltage. When the electric field strength is high enough, it can cause electrical breakdown of the air, leading to the formation of a plasma. This plasma emits light as excited electrons return to their ground state, creating the signature glow of Saint Elmo's fire.
03

Historical Significance

In history, sailors considered the appearance of St. Elmo's fire as an omen of sorts. While some believed it was a sign of protection from Saint Elmo, the patron saint of sailors, others thought it was a warning of an impending storm or disaster. Since it usually occurs during stormy weather conditions, it provided sailors with a visible hint of potential dangers.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Corona Discharge
Corona discharge is a process that naturally occurs under conditions where a high electrical field strength is present. This could be at the tips of ship masts, aircraft wings, or even pointed metal structures during stormy weather.

Here's how it works: the electrical field around the pointed tips becomes so strong that it starts to 'pull' electrons away from air molecules. This leads to the surrounding air getting charged, or ‘ionized’, emitting a visible glow known as a corona. This type of electrical discharge is often seen as a precursor to a full electrical breakdown and can serve as a warning sign of high voltage in the near vicinity.
Ionization of Air Molecules
Ionization of air molecules is central to the phenomenon of St. Elmo's fire. This is when the molecules of air lose or gain an electron due to a very strong electric field.

Imagine each air molecule as a tiny speck that can barely hold onto its electrons when the electric field around it becomes intense. The electrons get torn away, leaving the atom positively charged. These free electrons can then collide with other molecules, ionizing them as well, in a chain reaction. This process, which transforms the air into a conductor of electricity, is a crucial step in creating the luminous glow we see.
Atmospheric Electrical Phenomenon
St. Elmo's fire is not just a curiosity; it's an atmospheric electrical phenomenon that quite literally illuminates the complexity of our planet's weather systems.

It typically manifests alongside thunderstorms, where the dynamics of our atmosphere generate powerful electric fields. The spectacle of St. Elmo's fire is therefore a visual representation of the electrical activity taking place overhead, serving as a natural barometer for electrical conditions in the atmosphere. While it can be beautiful, it's also a reminder of nature's power and the volatile conditions that can arise in our environment.
Electrical Breakdown
Electrical breakdown is when a current suddenly starts flowing through a material that is normally an insulator, like air, because the electric field strength exceeds a critical level.

For St. Elmo's fire to appear, the electrical field around a pointed object must be high enough to cause such a breakdown of the air. At this tipping point, air becomes plasma, a state of matter that's like a gas but with some of the particles ionized, meaning they have become electrically charged. This plasma is capable of conducting electricity, and when the free electrons and ions recombine, they release energy in the form of light, which is the glow you see in St. Elmo's fire.
Plasma in Physics
In the context of St. Elmo's fire, plasma plays a critical role. Plasma is often called the fourth state of matter, alongside solids, liquids, and gases.

It's a soup of free electrons and ions - atoms that have lost or gained electrons. Plasma is highly conductive and can be created when the energy provided (for example, from an electric field) is enough to strip electrons from their atoms. In our atmosphere, this usually requires a situation like a strong thunderstorm. The glow of St. Elmo's fire comes from the plasma when the electrons recombine with ions, releasing light in a process called recombination radiation.

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Most popular questions from this chapter

A solid nonconducting sphere of radius \(a\) has a total charge \(+Q\) uniformly distributed throughout its volume. The surface of the sphere is coated with a very thin (negligible thickness) conducting layer of gold. A total charge of \(-2 Q\) is placed on this conducting layer. Use Gauss's Law to do the following. a) Find the electric field \(E(r)\) for \(ra\) (outside the coated sphere, beyond the sphere and the gold layer). c) Sketch the graph of \(E(r)\) versus \(r\). Comment on the continuity or discontinuity of the electric field, and relate this to the surface charge distribution on the gold layer.

An electric dipole consists of two equal and opposite charges situated a very small distance from each other. When the dipole is placed in a uniform electric field, which of the following statements is true? a) The dipole will not experience any net force from the electric field; since the charges are equal and have opposite signs, the individual effects will cancel out. b) There will be no net force and no net torque acting on the dipole. c) There will be a net force but no net torque acting on the dipole. d) There will be no net force, but there will (in general) be a net torque acting on dipole.

At which of the following locations is the electric field the strongest? a) a point \(1 \mathrm{~m}\) from a \(1 \mathrm{C}\) point charge b) a point \(1 \mathrm{~m}\) (perpendicular distance) from the center of a \(1-\mathrm{m}\) -long wire with \(1 \mathrm{C}\) of charge distributed on it c) a point \(1 \mathrm{~m}\) (perpendicular distance) from the center of a \(1-\mathrm{m}^{2}\) sheet of charge with \(1 \mathrm{C}\) of charge distributed on it d) a point \(1 \mathrm{~m}\) from the surface of a charged spherical shell of charge \(1 \mathrm{C}\) with a radius of \(1 \mathrm{~m}\) e) a point \(1 \mathrm{~m}\) from the surface of a charged spherical shell of charge \(1 \mathrm{C}\) with a radius of \(0.5 \mathrm{~m}\)

Consider an electric dipole on the \(x\) -axis and centered at the origin. At a distance \(h\) along the positive \(x\) -axis, the magnitude of electric field due to the electric dipole is given by \(k(2 q d) / h^{3} .\) Find a distance perpendicular to the \(x\) axis and measured from the origin at which the magnitude of the electric field stays the same.

\( \mathrm{~A}+48.00-\mathrm{nC}\) point charge is placed on the \(x\) -axis at \(x=4.000 \mathrm{~m},\) and \(\mathrm{a}-24.00-\mathrm{n} \mathrm{C}\) point charge is placed on the \(y\) -axis at \(y=-6.000 \mathrm{~m} .\) What is the direction of the electric field at the origin?
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