## 10.2 Magnetic field associated with a present (ESBPS)

If you host a compass close to a wire with which existing is flowing, the needle on the compass will be deflected.

You are watching: The moving charge in the wire causes the compass to deflect; this is because

Since compasses work by pointing follow me magnetic field lines, this way that there need to be a magnetic field near the wire v which the current is flowing.

The magnetic field developed by one electric current is constantly oriented perpendicular come the direction the the existing flow. Below is a map out of what the magnetic field approximately a cable looks like as soon as the wire has a current flowing in it. We usage (vecB) to denote a magnetic field and also arrows on ar lines to show the direction of the magnetic field. Note the if over there is no existing there will be no magnetic field.

The direction that the current in the conductor (wire) is presented by the central arrow. The one are ar lines and they likewise have a direction suggested by the arrows ~ above the lines. Comparable to the instance with electrical field lines, the better the number of lines (or the closer they room together) in one area the more powerful the magnetic field.

Important: all of our discussion regarding field direction assumes that we are managing conventional current.

To help you visualise this situation, was standing a pen or pencil right up ~ above a desk. The circles room centred roughly the pencil or pen and also would be attracted parallel come the surface of the desk. The reminder of the pen or pencil would allude in the direction the the present flow.

You can look at the pencil or pen from above and the pencil or pen will be a dot in the center of the circles. The direction the the magnetic ar lines is counter-clockwise for this situation.

To make it easier to see what is happening we are just going to draw one set of circular areas lines however note that this is simply for the illustration.

If you placed a piece of paper behind the pencil and look in ~ it indigenous the side, climate you would certainly be seeing the circular field lines side on and it is hard to understand that they room circular. Lock go with the paper. Psychic that ar lines have actually a direction, so once you space looking in ~ the item of file from the side it means that the circles enter the record on one next of the pencil and come out of the document on the other side.

When us are illustration directions of magnetic fields and also currents, we usage the icons (odot) and also (otimes). The price (odot) to represent an arrow that is coming out of the page and the price (otimes) to represent an arrowhead that is going into the page.

It is basic to remember the definitions of the symbols if friend think of an arrowhead with a sharp tip at the head and a tail with feathers in the shape of a cross.

The Danish physicist, Hans Christian Oersted, to be lecturing sooner or later in 1820 top top the opportunity of electricity and also magnetism being pertained to one another, and in the procedure demonstrated the conclusively through an experiment in prior of his entirety class. By happen an electric present through a steel wire suspended over a magnetic compass, Oersted to be able to develop a definite activity of the compass needle in response to the current. What started as a guess in ~ the start of the course session was shown as reality at the end. Needless come say, Oersted had actually to revise his lecture notes for future classes. His exploration paved the method for a whole brand-new branch of scientific research - electromagnetism.

We will now look at three examples of present carrying wires. For each example we will determine the magnetic field and draw the magnetic ar lines around the conductor.

### Magnetic field roughly a right wire (ESBPT)

The direction of the magnetic field around the present carrying conductor is shown in figure 10.1.

number 10.1: Magnetic field about a conductor once you look in ~ the conductor native one end. (a) present flows the end of the page and the magnetic ar is counter-clockwise. (b) existing flows into the page and also the magnetic field is clockwise.
figure 10.2: Magnetic fields roughly a conductor looking down on the conductor. (a) existing flows clockwise. (b) present flows counter-clockwise.

## Direction of a magnetic field

Using the directions given in figure 10.1 and Figure 10.2 shot to find a ascendancy that conveniently tells you the direction the the magnetic field.

Hint: use your fingers. Hold the cable in her hands and shot to uncover a link in between the direction of your thumb and the direction in which her fingers curl.

There is a simple an approach of recognize the relationship between the direction the the current flowing in a conductor and the direction that the magnetic field about the same conductor. The technique is referred to as the Right Hand Rule. Just stated, the ideal Hand dominion says the the magnetic field lines produced by a current-carrying wire will certainly be oriented in the same direction as the curled fingers of a person"s right hand (in the “hitchhiking” position), with the thumb pointing in the direction that the current flow.

Your ideal hand and also left hand are unique in the feeling that you can not rotate one of them to it is in in the same position as the other. This way that the appropriate hand part of the rule is essential. Friend will always get the not correct answer if you usage the wrong hand.

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## The best Hand Rule

Use the ideal Hand dominance to attract in the direction of the magnetic fields for the following conductors v the currents flow in the directions shown by the arrows. The an initial problem has actually been completed for you.

 1 2 3 4 5 6 7 8 9 10 11 12

## Magnetic field roughly a current carrying conductor

### Apparatus

one ( ext9) ( extV) battery v holder

two hookup wires with alligator clips

compass

stop watch

### Method

Connect her wires to the battery leaving one finish of each wire unconnected so that the circuit is no closed.

Be certain to limit the current flow come ( ext10) ( extseconds) at a time (Why you can ask, the wire has very little resistance top top its own so the battery will certainly go flat really quickly). This is to keep battery life and also to prevent overheating the the wires and battery contacts.

Place the compass close come the wire.

Close the circuit and observe what wake up to the compass.

Reverse the polarity that the battery and close the circuit. Watch what happens to the compass.

### Conclusions

Does a present flowing in a wire create a magnetic field?

Is the magnetic field present when the current is no flowing?

Does the direction that the magnetic field produced by a current in a wire count on the direction the the present flow?

How go the direction the the current influence the magnetic field?

### Magnetic field around a current carrying loop (ESBPV)

So far we have actually only looked at directly wires carrying a current and the magnetic fields roughly them. We are going to research the magnetic field collection up by circular loops that wire carrying a current because the ar has an extremely useful properties, for example you will see that we can collection up a uniform magnetic field.

## Magnetic field about a loop of conductor

Imagine two loops make from cable which bring currents (in opposite directions) and are parallel to the web page of your book. By using the ideal Hand Rule, attract what girlfriend think the magnetic field would look like at various points around each the the two loops. Loop 1 has actually the present flowing in a counter-clockwise direction, if loop 2 has actually the current flowing in a clockwise direction.

If you make a loop of current carrying conductor, climate the direction of the magnetic field is derived by using the right Hand dominance to different points in the loop.

Notice the there is a variation on the ideal Hand Rule. If you do the fingers of your ideal hand follow the direction the the existing in the loop, your ignorance will allude in the direction whereby the field lines emerge. This is comparable to the north pole (where the field lines emerge from a bar magnet) and shows girlfriend which side of the loop would lure a bar magnet"s north pole.

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### Magnetic field about a solenoid (ESBPW)

If us now include another loop through the existing in the very same direction, climate the magnetic field roughly each loop can be added together to produce a more powerful magnetic field. A coil of plenty of such loops is referred to as a solenoid. A solenoid is a cylindrical coil of wire acting together a magnet once an electric present flows v the wire. The magnetic field pattern about a solenoid is comparable to the magnetic ar pattern around the bar magnet the you learned in great 10, which had a identify north and also south pole as shown in number 10.3.

number 10.3: Magnetic field approximately a solenoid.

### Real-world applications (ESBPX)

Electromagnets

An electromagnet is a piece of wire intended to create a magnetic field with the passage of electric existing through it. Though all current-carrying conductors produce magnetic fields, an electromagnet is usually constructed in such a means as to maximise the strength of the magnetic ar it produces because that a special purpose. Electromagnets are commonly used in research, industry, medical, and consumer products. An instance of a frequently used electromagnet is in protection doors, e.g. Top top shop doors which open automatically.

As one electrically-controllable magnet, electromagnets type part the a wide selection of “electromechanical” devices: devices that develop a mechanical force or motion through electric power. Maybe the most evident example of such a machine is the electric motor which will be described in information in class 12. Other examples of the use of electromagnets are electric bells, relays, loudspeakers and also scrapyard cranes.

## Electromagnets

### Aim

A magnetic ar is developed when an electric existing flows with a wire. A solitary wire go not produce a solid magnetic field, but a wire coiled around an iron main point does. We will investigate this behaviour.

### Apparatus

a battery and also holder

a length of wire

a compass

a couple of nails

### Method

If you have actually not excellent the vault experiment in this chapter execute it now.

Bend the wire right into a series of coils prior to attaching it come the battery. Observe what wake up to the deflection the the needle on the compass. Has the deflection that the compass get an impression stronger?

Repeat the experiment by an altering the number and also size of the coils in the wire. Observe what happens to the deflection top top the compass.

Coil the wire approximately an iron nail and then attach the coil come the battery. Observe what happens to the deflection of the compass needle.

### Conclusions

Does the variety of coils impact the toughness of the magnetic field?

Does the iron nail rise or diminish the stamin of the magnetic field?

## Overhead power lines and the environment

### Physical impact

Power lines room a usual sight all throughout our country. This lines carry power native the strength stations to our homes and also offices. Yet these strength lines deserve to have an unfavorable impacts top top the environment. One risk that castle pose is to birds which fly right into them. Conservationist Jessica Shaw has actually spent the last few years looking at this threat. In fact, strength lines attitude the major threat come the blue crane, southern Africa"s national bird, in the Karoo.

“We are lucky in southern Africa to have a wide variety of bird species, including many big birds choose cranes, storks and also bustards. Unfortunately, there are likewise a most power lines, which can influence on bird in two ways. They can be electrocuted as soon as they perch on some species of pylons, and also can also be killed by colliding v the line if castle fly right into it, either from the impact with the line or from hitting the ground afterwards. These collisions often happen to big birds, which room too hefty to avoid a power line if they just see it in ~ the critical minute. Various other reasons the birds might collide include bad weather, paris in flocks and also the lack of experience of younger birds.

Over the past couple of years we have been researching the serious influence that power line collisions have on Blue Cranes and also Ludwig’s Bustards. These are two of our endemic species, which means they space only uncovered in southern Africa. They room both large birds that have actually long lifespans and also breed slowly, for this reason the populations could not recoup from high mortality rates. We have actually walked and also driven under power lines across the Overberg and the Karoo to counting dead birds. The data show that thousands of these bird are killed by collisions every year, and Ludwig’s Bustard is now provided as an Endangered types because of this high level the unnatural mortality. We are also looking for methods to reduce this problem, and also have to be working v Eskom come test various line noting devices. Once markers are held on power lines, birds might be able to see the strength line from more away, which will offer them enough time to prevent a collision.”

### Impact of fields

The reality that a ar is created around the strength lines means that they have the right to potentially have an influence at a distance. This has actually been studied and continues to it is in a object of far-reaching debate. At the time of writing, the world Health organization guidelines for human being exposure come electric and magnetic areas indicate that there is no clean link in between exposure to the magnetic and also electric areas that the general public to meet from strength lines, since these are extremely low frequency fields.

Power line noise have the right to interfere through radio communications and broadcasting. Essentially, the strength lines or associated hardware improperly generate undesirable radio signals the override or compete with wanted radio signals. Power line noise can affect the top quality of radio and also television reception. Disruption of radio communications, such together amateur radio, can additionally occur. Ns of an important communications, such as police, fire, military and other similar users of the radio spectrum, can an outcome in even much more serious consequences.

Group discussion:

Discuss the over information.

Discuss other methods that strength lines impact the environment.

When lightning strikes a ship or one aeroplane, it can damages or otherwise readjust its magnetic compass. There have actually been recorded instances that a lightning strike transforming the polarity of the compass for this reason the needle point out south rather of north.

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If you host a compass near a wire with which current is flowing, the needle top top the compass will certainly be deflected. Since compasses job-related by pointing follow me magnetic ar lines, this way that there need to be a magnetic field near the wire through which the current is flowing. If the existing stops flowing the compass returns to its initial direction. If the present starts to circulation again climate the deflection happens again.