Investigation of determination of flux density of magnets(plane)

Investigation of determination of flux density of magnets

Introduction

A magnet is a material or object that produces a magnetic field. A low-tech means to detect a magnetic field is to scatter iron filings and observe their pattern, as in the accompanying figure. A ‘hard’ or ‘permanent’ magnet is one that stays magnetized, such as a magnet used to hold notes on a refrigerator door. Permanent magnets occur naturally in some rocks, particularly lodestone, but are now more commonly manufactured. A ‘soft’ or ‘impermanent’ magnet is one that loses its memory of previous magnetizations. ‘soft’ magnetic materials are often used in electromagnets to enhance the magnetic field of a wire that carries an electrical current and is wrapped around the magnet; the field of the ‘soft’ magnet increases with the current.

As current flows through a wire, the wire is magnetized and it generates a magnetic field around it, and this magnetic field will interact with any other magnetic field to produce a magnetic force. We can predict the direction of force by using Fleming’s left-hand rule. There are three things here, all of which are mutually at right angles to each other: the magnetic field, the current in the wire, and the magnetic force acting on the wire. These can be represented by holding the thumb and first two fingers of your left hand so that they are mutually at right angles.

Fingers represent:

Thumb shows the direction of the movement ( the force )

The first finger shows the direction of the field

The second finger shows the direction of the current

The production of this force is known as the motor effect, because this force is used in electric motors. I a simple motor, a current flowing in a coil produce a magnetic field; this field interacts with a second field produced by a permanent magnet.

Magnetic flux is a measure of quantity of magnetism, taking into account the strength and the extent of ...

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Fingers represent:

Thumb shows the direction of the movement ( the force )

The first finger shows the direction of the field

The second finger shows the direction of the current

Magnetic flux is a measure of quantity of magnetism, taking into account the strength and the extent of a magnetic field. the flux through an element of area perpendicular to the direction of magnetic field is given by the product of the magnetic field and the are element. More generally, magnetic flux is defined by a scalar product of the magnetic field and area element vector.

Magnetic flux density used to describe the amount of flux flowing through unit area at a point in the field. The symbol used for flux density is B, and its unit is the tesla, T.

In this experiment, I am going to use a current balance to investigate the force on a current-carrying conductor in a magnetic field . A current flow through the wire frame; the magnetic field pushes the frame downwards, we can work out the direction of the motion by using the Fleming’s left-hand rule. By adding small weights to the other side of the frame, I can finally make the balance go the equilibrium. There fore the magnetic force is equal the restoring weight. In this case, I will use some little pieces of paper as they are small and light enough to get an quite accurate mass value.

The size of the magnetic force depends on:

The magnetic field strength, B

The current I, flowing at right angles to the field

The length l of the conductor I the magnetic field. ( in this case, the length of the conductor will be the length of the magnet)

Sum up these three factor, we can get an equation for the force:

F = BIl

We can see from this equation that the force F, is proportional to each of these quantities.

we can arrange the formula:

B = F/Il

A magnetic field has a strength of one tesla ( 1T ) , if it exerts a force of 1N on a conductor of length 1m, carrying a current of 1A at right angles to the field. Thus the equation b = F/Il defines the quantity magnetic field strength( flux density) B, and its unit, the tesla: 1T = 1NA-1m-1

As the force of magnetic is equal to the restoring weight, the length of the conductor can be measured by measuring the length of magnet, and the current can be measured by an ammeter. Therefore the magnetic flux density can be calculated easily.

There are few factors which I think would affect my experiment:

The current flowing in the wire

Because the stronger the current, the bigger the magnetic field it is generated, therefore the magnetic force would be bigger. As I am going to find out the magnetic flux of the magnet not the wire, so this factor is not going to be concerned. And also I will use a variable resistance to vary the current to get different values so that enable me to plot a graph.

The material the core is made of

Different materials have different resistivity, so that the amount of current flow in each material is different. In this case, I am going to use copper wire because it has very little resistance so that current can easy to flow.

To keep this a fair test and get a reliable and accurate results, I will use the same wire as it will have the same amount of resistance and I will use the same balance each time to weight my stored papers so that to give me the same accurate figure. The same power supply will be used as some power supplies give out different voltage even if the difference is small.

Equipment & Justification

Tow magnets (which have the exactly the same size).

This ensure that they have the same length( length of the conductor in the magnetic field) and the same magnetic flux.

D.C power supply

This makes the current flow in the same direction.

Current balance with copper wire on it

Less resistance, current can easy to flow

Small paper pieces

These are used to add to the other side of the frame, and make the current balance go the equilibrium. As they are small and light enough, so that to give more accurate results.

An electronic balance

As it is electronic, and it will give the value up to 2 decimal places, so that produce more accurate results.

Copper wires

Variable resistor

This is used to vary the resistance in the circuit to give different current.

An ammeter

This is used to measure the amount of current

Safety

Wearing goggles

Watching out the current, if it gets to large, the wire could be burnt or get to hot. Make sure do not touch the wire if it gets too hot.

Method

set up equipments like the diagram

switch on the power supply and vary the variable resistance, record the current shown on the ammeter and adding paper pieces on to the frame

as soon as the current balance goes to equilibrium which can be seen by comparing the level of two frame on each side, to see if they are at the same level, and switch of the power supply