PHYSICS PROJECT NETURAL POINT OF A MAGNET

Transcription

1 PHYSICS PROJECT NETURAL POINT OF A MAGNET MADE BY : UMANG GUPTA 12-B 41 1 P a g e

2 Pages attached TOPIC 1 Certificates 2 Acknowledgement 3 Preface 4 Introduction 5 Aim 6 Apparatus 7 Theory 8 Procedure 9 Observations 10 Calculations 11 Result 12 Precautions 2 P a g e

3 CERTIFICATE This is to certify that Umang Gupta of class XII-B has performed the experiment entitled " To determine the location of Neutral points and calculate the Dipole Moment of Bar Magnet given". Under the supervision of Ma'am Rakhi Thapar and lab assistant Naveen Sir 3 P a g e Mrs. Rakhi Thapar (Physics Department)

4 Montfort School ACKNOWLEDGEMENT I, Umang Gupta, of class XII-B sincerely acknowledge my Physics teacher Rakhi Thapar for her invaluable support in selecting this extremely important project. I express my gratitude for her knowledgeable suggestions, comments, advice and guidance throughout. I would also like to thank the lab assistant Mr. Naveen, for providing me with the necessary information and apparatus Umang Gupta XII -B Roll No: 41 4 P a g e

5 PREFACE I chose to perform this experiment, to locate the neutral point, as an extension to the theory we have already learnt in the class. We have been taught that a point in the magnetic field where the fields due to the bar magnet is equal and opposite to the horizontal intensity of Earth's magnetic field. I feel the observations made in the experiment and the conclusion drawn from them complement the concept by verifying it sufficiently. 5 P a g e

6 INTRODUCTION Magnetism is a class of physical phenomena that are mediated by magnetic fields. Electric currents and the magnetic moments of elementary particles give rise to a magnetic field, which acts on other currents and magnetic moments. Every material is influenced to some extent by a magnetic field. The most familiar effect is on permanent magnets, which have persistent magnetic moments caused by ferromagnetism. The prefix Ferro- refers to iron, because permanent magnetism was first observed in a form of natural iron ore called magnetite, Fe3O4. Most materials do not have permanent moments. Some are attracted to a magnetic field (paramagnetic); others are repulsed by a magnetic field (diamagnetism); others have a more complex relationship with an applied magnetic field (spin glass behavior and antiferromagnetism). Substances that are negligibly affected by magnetic fields are known as non-magnetic substances. These include 6 P a g e

7 copper, aluminium, gases, and plastic. Pure oxygen exhibits magnetic properties when cooled to a liquid state. The magnetic state (or magnetic phase) of a material depends on temperature and other variables such as pressure and the applied magnetic field. Magnetism is a force of nature, which causes special kinds of objects to attract to each other. Magnetism is all around you. You can find it in the most common places like the magnet on your refrigerator. The force of magnetism flows from one pole to another. A pole is the point where the force is pointed. The force of magnetism causes material to point along the direction the magnetic force points. This means that the force has direction. The force is represented by lines, which point from the positive pole to the negative pole of the magnet. It forces small pieces of iron to live up in the direction the magnet 7 P a g e

8 force points. The lines represent what is called the magnetic field of the magnet. The magnetic field is strongest where the lines of force come together, and is weakest when the lines of force are far apart.. A magnet is surrounded by a magnetic field. This field has both a North side, and a South side. This field is strongest where the lines of force came together and weakest when they are far apart. Flux lines are the lines that determine how current flows throughout a magnet. They are circular lines, which run around the magnet. It is determined which direction a current is flowing by using a series of left-hand rules. Each magnet has its own flux shape, and rule. 8 P a g e

9 Magnetism and electricity are very closely related. When speaking of them together they are spoken of as an electromagnetic force. There are three main factors that must be thought of when realizing that magnetism and electricity are related. These things are a) moving electric charges produce magnetic fields, b) magnetic fields exert forces on moving electric charges, c) when you change magnetic fields in the presence of electric charges it causes a current to flow. Magnetism is present throughout the world. It is used in electronics, medicine, generators, and in so many other things. Magnetism affects all aspects of our lives. 9 P a g e

10 AIM To determine the location of neutral points and calculate the dipole moment of bar magnet given APPARATUS A Drawing Board A Compass Needle A Bar Magnet A plain sheet of paper Fixing pins Meter Scale 10 P a g e

11 THEORY The Magnetic Field : When the charged particle move through a magnetic field B, it feels Lorentz force F given by the cross product F = Q (V x B) where Q is the electric charge of the particle and V is the velocity vector of the particle Because this is a cross product, the force is perpendicular to both the motion of the particle and the magnetic field. It follows that the magnetic force does not work on the particle, it may change the direction of the particle's movement, but it cannot cause it to speed up or slow down. The magnitude of the force is 11 P a g e

12 F= QVBsin Ɵ where Ɵ is the angle between the V and B vectors The magnetic field lines: The magnetic field lines are a visual and intuitive realization of the magnetic field. Their properties are The magnetic field lines of a magnet(or a solenoid) gorm continuous closed loops. This is unlike the electric dipole where these fileds lines begin from a positive charge and end on a negative charge or escape to infinity. The tangent to the field line at a given point represents the direction of the net magentic field B at that point Lines of force : Lines of force is a closed imaginary curve starting from the North Pole and ending in the South pole in the magnetic field such that the tangent drawn at any point o the curve gives the direction of resultant magentic field at that point. 12 P a g e

13 13 P a g e The Dipole : A very common source of magentic field shown in the nature is dipole, with a "south pole" and a "north pole", terms dating back to the use of magnets as compass, interacting with the Earth's magnetic field to indicate the North and South Pole. Since the opposite ends of the magnets are attracted, the North Pole of a magnet attracted to the south pole of another magnet. The Earth's North Magnetic Pole (currently in the Arctic Ocean, north of Canada) is physically a south pole as it attracts the North Pole of a compass. A magnetic field contains energy, and physical systems move around configurations with lower energy. When diamagnetic material is placed in a magnetic field, a magnetic dipole tends to align itself in opposed polarity to that filed, thereby lowering the net filed strength. When ferromagnetic material is placed within a magnetic field, the dipoles align to the applied force, thus expanding the domain walls of the magnetic domains. The magnetic Dipole Moment: The magnetic moment of a magnet is a quantity that determines the torque it will experience in an external magnetic field. A loop of electric current, a bar magnet, an electron, a molecule, and a planet all have magnetic moments. The magnetic moment may

14 be considered to be a vector having magnitude and direction. The direction of magnetic moment points from south to the North Pole of the magnet. The magnetic field produced by the magnet is proportional to its magnetic moment. More precisely, the term magnetic moment normally refers to a system's magnetic dipole moment, which produce the first term in the multiple expansion of a general magnetic field. The dipole component of an object's magnetic field is symmetric about the direction of its magnetic dipole moment, and decreases as the inverse cube of the distance from the object. EARTH'S MAGNETIC FIELD Elements of the Earth's Magnetic field: Earth's magnetic field, also known as the geomagnetic field, is the magnetic field that extends from Earth's interior to where it meets the solar wind, a stream of charged particles emanating from the sun. Its magnitude at the Earth's surface ranges from microstela( gauss). It is approximately the field of a magnetic dipole titled at an angle of 10 degrees with respect to Earth's rotational axis, as if 14 P a g e

15 15 P a g e there were a bar magnet placed at that angle at the Center of the Earth, unlike a bar magnet, however. Earth's magnetic field changes over time because it is generated by a geodynamo(in the Earth's case, the molten iron alloy in its outer core) The North Magnetic Pole wander sufficiently slowly to keep ordinary compasses useful for navigation. At random intervals, however, are averaging around several hundred thousand years, the Earth's field reverses and the North and South Magnetic poles switch places. These reversals of the geomagnetic poles leave a record in rocks that allow paleomagnetists to calculate past motions of continents and ocean floors as a result of platetoctonics. The magnetosphere is a region above the ionosphere and extends several tens of thousands kilometers into space, protecting the Earth from cosmic rays that would otherwise strip away the upper atmosphere, including the ozone layer that protects the Earth from harmful ultraviolet radiations. The magnetosphere is the region above the ionosphere and extends several tens of thousands of kilometers into space, protecting the Earth from

16 16 P a g e cosmic rays that would otherwise strip away the upper atmosphere, including the ozone layer that protects the Earth from harmful ultraviolet radiations. Dipolar Approximations : Near the surface of the Earth, its magnetic field can be closely approximated by the field of a magnetic Dipole positioned at the center of the Earth and tilted at an angle of about 10 degree with respect to the rotational axis of the Earth. The dipole is roughly equivalent to a powerful bar magnet, with its south pole pointing towards the geomagnetic North Pole. This may seem surprising, but the North Pole of a magnet is so defined because, if allowed to rotate freely, it points roughly northwards(in the geographic sense). Since the north pole of a magnet attracts the south poles of other magnet and repels the North Pole, it must be attracted to the south pole of the Earth's Magnet. The dipolar field accounts for 80% to 90% of the field in most locations. Intensity : The intensity of the field is often measured in gauss(g),but is generally reported in nanostela(nt), with 1 G = 100,000 nt. A nanastela is also referred to as gamma (ɣ). The telsa is the SI unit of the magnetic field, B. The field ranges between (25,000 to 65,000 nt) (0., G). By comparison, a strong

17 refrigerator magnet has a field of about 100 gauss(0.010 T). NEUTRAL POINT As a result of two magnetic fields acting at the same place, the resultant field has a special feature. At a particular point, if the compass needle does not point in any particular direction, then there is no net magnetic field at that point. Such a point is called Neutral Point or the Null point. A Neutral point is a point where the resultant magnetic field is zero. 17 P a g e

18 PROCEDURE Stretch sheet of paper over the drawing board. Fix it with pins Place the compass needle over the plain sheet of paper so as to determine the geographic North and South. This can be done by rotating the drawing board Point at which the Red Cross mark and the meddles of the compass coincide is the geographic North and South. Then the corresponding North and South poles with geographic North and South poles Then remove the compass and draw lines along these points, these pass the axis 18 P a g e

19 Place the bar magnet along the North of the geographic North. Keeping it in mind that white dot signifies the North Pole if the bar magnet Now draw the outline of the bar magnet Place the compass needle at different points around the magnet and trace the points Place the needle at the subsequent position such that one end of it coincides with dots already dotted. Continue the process till the number of dots are obtained. After drawing several lines of forces, we get the final plot. Then find the neutral points( the points at which there is no deflection of needle). So, there are two neutral points. When we remove the bar magnets, we get the final plot of magnetic lines of forces. 19 P a g e

20 OBSERVATIONS Let, B be the horizontal component of the Earth's Magnetic field in Delhi M be the magnitude of the magnetic field d be the distance of neutral points from the centre of the Bar Magnet 2l be the length of the Bar Magnet m is the pole strength of the Bar Magnet The observation of the sheet is attached on next page 20 P a g e

21 CALCULATIONS The horizontal component of earth's magnetic field in Delhi (B ʜ) = 3.2 x 10 (given) According to the observation sheet: Distance of neutral point from centre of the bar 0.38 magnet (2d) = m 0.06 Length of the Bar Magnet (2l) = m B = We know that, μ 2Md 4π (d² - l² ) ² At netural point, B = B ʜ = 0.33 X 10^-4 T 21 P a g e

22 B ʜ = μ 2Md 4π (d² - l² ) ² M = B ʜ 4π (d² - l² ) ² where 2μ d μ = 4π x 10^-7 M = m x 2l m = M /2l 22 P a g e

23 RESULT The neutral points are at a distance of M from the centre of the Bar Magnet with its North Pole pointing to the geographic North. The Magnitude of the magnetic field is am ² The pole strength of the Bar Magnet is Am 23 P a g e

24 PRECAUTIONS All the point must be traced very accurately and neatly using a compass The North Pole of the bar magnet must be placed along the direction of geographic North A sharp pencil must be used to draw all the magnetic lines of forces Distance of neutral points must be measured from the centre of Bar Magnet 24 P a g e

25 BIBLOGRAPHY The following books assisted and inspired me in my Endeavour of completing this experiment as my practical work PHYSICS TEXT BOOK OF CLASS XII(NCERT) FUNDAMENTAL OF PHYSICS BY WILEY -INDIA Lastly, I would like to mention about the inputs drawn by me from various sources 25 P a g e

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