How Do You Know if a Planet Has a Magnetic Field

Magnetic fields and how to make them

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Magnetism

In that location is a strong connectedness betwixt electricity and magnetism. With electricity, at that place are positive and negative charges. With magnetism, there are northward and s poles. Similar to charges, similar magnetic poles repel each other, while unlike poles concenter.

An important difference between electricity and magnetism is that in electricity it is possible to take individual positive and negative charges. In magnetism, north and south poles are e'er found in pairs. Single magnetic poles, known as magnetic monopoles, have been proposed theoretically, just a magnetic monopole has never been observed.

In the aforementioned fashion that electric charges create electrical fields around them, north and south poles will set up magnetic fields around them. Again, at that place is a deviation. While electric field lines begin on positive charges and stop on negative charges, magnetic field lines are closed loops, extending from the south pole to the north pole and dorsum once again (or, equivalently, from the northward pole to the southward pole and back again). With a typical bar magnet, for example, the field goes from the northward pole to the due south pole exterior the magnet, and back from south to northward inside the magnet.

Electrical fields come from charges. So do magnetic fields, but from moving charges, or currents, which are simply a whole bunch of moving charges. In a permanent magnet, the magnetic field comes from the movement of the electrons inside the material, or, more precisely, from something called the electron spin. The electron spin is a bit like the Earth spinning on its axis.

The magnetic field is a vector, the same style the electric field is. The electric field at a particular point is in the direction of the force a positive charge would experience if it were placed at that indicate. The magnetic field at a point is in the direction of the forcefulness a north pole of a magnet would experience if it were placed there. In other words, the north pole of a compass points in the management of the magnetic field.

One implication of this is that the magnetic due south pole of the Globe is located nearly to the geographic north pole. This hasn't always been the case: every once in a while (a long while) something changes inside the Earth'southward core, and the earth's field flips management. Even at the present time, while the Globe's magnetic field is relatively stable, the location of the magnetic poles is slowly shifting.

The symbol for magnetic field is the letter B. The unit is the tesla (T).

The magnetic field produced by currents in wires

The simplest electric current nosotros tin come up with is a current flowing in a straight line, such as along a long straight wire. The magnetic field from a such current-conveying wire actually wraps around the wire in circular loops, decreasing in magnitude with increasing distance from the wire. To discover the direction of the field, yous tin can use your right manus. If you lot curl your fingers, and point your thumb in the direction of the current, your fingers will point in the direction of the field. The magnitude of the field at a distance r from a wire carrying a electric current I is given by:

Currents running through wires of different shapes produce unlike magnetic fields. Consider a round loop with a current traveling in a counter-clockwise direction around it (as viewed from the peak). By pointing your thumb in the direction of the current, you should be able to tell that the magnetic field comes up through the loop, so wraps around on the outside, going back downwards. The field at the center of a circular loop of radius r carrying a electric current I is given by:

For North loops put together to form a flat coil, the field is just multiplied past Northward:

If a number of current-conveying loops are stacked on elevation of each other to form a cylinder, or, equivalently, a single wire is wound into a tight spiral, the effect is known every bit a solenoid. The field along the axis of the solenoid has a magnitude of:

where north = Northward/50 is the number of turns per unit length (or, in other words, the full number of turns over the full length).

The force on a charged particle in a magnetic field

An electrical field E exerts a forcefulness on a charge q. A magnetic field B will also exert a force on a accuse q, only only if the charge is moving (and non moving in a direction parallel to the field). The direction of the force exerted by a magnetic field on a moving accuse is perpendicular to the field, and perpendicular to the velocity (i.e., perpendicular to the direction the charge is moving).

The equation that gives the forcefulness on a charge moving at a velocity five in a magnetic field B is:

This is a vector equation : F is a vector, v is a vector, and B is a vector. The only thing that is not a vector is q.

Note that when five and B are parallel (or at 180�) to each other, the force is goose egg. The maximum force, F = qvB, occurs when v and B are perpendicular to each other.

The direction of the force, which is perpendicular to both 5 and B, tin be found using your correct hand, applying something known as the right-hand rule. 1 way to do the correct-hand rule is to do this: point all iv fingers on your right manus in the direction of v. So coil your fingers and then the tips point in the direction of B. If yous hold out your pollex as if you're hitch-hiking, your thumb will point in the direction of the strength.

At least, your thumb points in the direction of the strength every bit long as the charge is positive. A negative charge introduces a negative sign, which flips the management of the force. So, for a negative charge your correct hand lies to you, and the strength on the negative charge will be reverse to the management indicated past your right mitt.

In a compatible field, a charge initially moving parallel to the field would experience no force, then it would proceed traveling in straight-line movement, parallel to the field. Consider, however, a charged particle that is initially moving perpendicular to the field. This particle would experience a forcefulness perpendicular to its velocity. A force perpendicular to the velocity can only change the direction of the particle, and it tin't affect the speed. In this case, the force will send the particle into uniform round motion. The particle volition travel in a circular path, with the plane of the circumvolve being perpendicular to the direction of the field.

In this case, the force applied past the magnetic field ( F = qvB ) is the only force acting on the charged particle. Using Newton's second law gives:

The particle is undergoing compatible circular motion, so the acceleration is the centripetal dispatch:

a = v² / r

so, q v B = g v² / r

A factor of 5 cancels out on both sides, leaving

q B = m v / r The radius of the circular path is then: r = m five / (q B)

A particle that is initially moving at some angle between parallel and perpendicular to the field would follow a move which is a combination of circular motion and straight-line movement...it would follow a spiral path. The centrality of the spiral would be parallel to the field.

To understand this, simply dissever the velocity of the particle into two components:

The field does not affect v-parallel in whatever manner; this is where the straight line movement comes from. On the other hand, the field and v-perpendicular combine to produce circular motion. Superimpose the two motions and you get a spiral path.

Working in three dimensions

With the strength, velocity, and field all perpendicular to each other, we take to piece of work in three dimensions. It tin be hard to draw in three-D on a 2-D surface such equally a slice of paper or a chalk board, then to represent something pointing in the third dimension, perpendicular to the page or board, we normally describe the direction as either a circle with a dot in the center or a circle with an X in the middle.

Think of an pointer with a tip at one end and feathers at the other. If y'all await at an arrow coming toward yous, yous see the tip; if you await at an arrow going away from you, you see the X of the feathers. A circle with a dot, then, represents something coming out of the folio or board at you; a circle with an X represents something going into the folio or board.

The post-obit diagram shows the path followed by two charges, one positive and one negative, in a magnetic field that points into the page:

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How Do You Know if a Planet Has a Magnetic Field

Source: http://physics.bu.edu/~duffy/PY106/MagField.html

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