SCHOOL NAME SCHOOL NAME SCHOOL NAME - ammhu.com · Aim/ Objective 2. Apparatus Required 3. Theory 4. Procedure 5. Observation 6. Calculation 7. Result 8. Precautions 9. Bibliography

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www.ammhu.com A categorized blogging website and an Online Resource Centre For CBSE, RBSE, and Other State Boards — Raj Kumar Parashari, Head Science @ JPHS, Jaipur-302021

SCHOOL NAME SCHOOL NAME SCHOOL NAME

ADDRESS WITH PINCODE AND PHONE NUMBER

Submitted by Guided by

Student Name [ Teacher Name ]

XII Sc ……

Board Roll No. Designation

-----------

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INDEX

I. Certificate

II. Acknowledgement

1. Aim/ Objective

2. Apparatus Required

3. Theory

4. Procedure

5. Observation

6. Calculation

7. Result

8. Precautions

9. Bibliography

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CERTIFICATE

This is to certify that _______________________

student of ______ school name _______, class XII Sc __

has carried out his work for the investigatory project

entitled _______________________________________

under my guidance and supervision.

Signature of the Teacher

Name Of The Teacher

Designation

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ACKNOWLEDGEMENT

I __________________________________ a student of

____________________________________,______________

would like to pay my sincere gratitude to my Physics teacher

Mr./Mrs. __________________________ for helping and

guiding me throughout the completion of the project report. I

would like to thank Mr./Mrs. _______________________ our

school principal/Director for making school such a wonderful

place of learning. I also would like to thank Mr.

______________ our lab assistant for the timely assistant in

completion of the project.

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1. AIM

To Draw magnetic field lines of Earth;

(a) in the absence of a bar magnet;

(b) in the presence of a bar magnet in N-S configuration. Also,

find magnetic moment of the bar magnet.

2. APPARATUS REQUIRED

A drawing board, sheets of paper (A3), pins, scale, compass, bar

magnet.

3. THEORY

According to Faraday, magnetic field line is an imaginary

curve, the tangent to which at any point gives us the direction of

magnetic field at that point. If we imagine a number of small

compass needles around a magnet each compass needle

experiences a torque due to the field of the magnet. The torque

acting on a compass needle aligns it in the direction of the

magnetic field. ―The path along which the compass needles are

aligned is known as magnetic field line.

PROPERTIES OF MAGNETIC FIELD LINES

a. The magnetic field lines of a magnet form closed

continuous loops.

b. Outside the body of the magnet, the direction of magnetic

field lines is from North Pole to South Pole.

c. At any given point, tangent to the magnetic field times

represents the direction of net magnetic field B at that point.

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d. The magnitude of magnetic field at any point is represented

by the number of magnetic field lines passing normally through

unit area around that point.

e. No two magnetic field lines can intersect each other.

MAGNETIC FIELD OF EARTH

Sir William Gilbert was the first to suggest in the year 1600, that

earth itself a huge magnet. The branch of Physics which deals

with the study of magnetism of earth is called terrestrial

magnetism or geomagnetism. Earth’s magnetic field is fairly

uniform. The strength of this field at the surface of Earth is

approximately 510

tesla. The field is not only confined to Earth’s

surface. It extends up to a height nearly 5 times the radius of

earth kmkm 3200064005 .

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MAGNETIC ELEMENTS OF EARTH

Magnetic elements of earth at a place are the quantities which

describe completely in magnitude and direction, the magnetic

field of earth at that place.

Following are the three magnetic elements of earth:

a. Magnetic declination

b. Magnetic inclination or angle of magnetic dip

c. Horizontal component (BH).

a. Magnetic declination

The small angle between magnetic axis and geographic

axis at a place is defined as the magnetic declination at the

place. It is represented by .

b. Angle of Magnetic Dip or magnetic Inclination

Magnetic dip or magnetic inclination at a place is defined

as the angel which the direction of total strength of earth’s

magnetic field makes with a horizontal line in magnetic

meridian. It is represented by . The value of magnetic dip at a

place can be measured using an instrument called ‘dip circle’

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c. Horizontal component

It is the component of total intensity of earth’s magnetic

field along the horizon of the place and in the direction of

magnetic meridian. It is represented by BH =B cos . The value

of BH at a place on the surface of earth is of the order of 3.2

×10–5 tesla.

MAGNETIC FIELD AT A POINT ON THE MAGNETIC AXIS

The magnetic fields at a point P on its axis due to the two poles

are given by

0N 2

mB

4 (r )

; along NP

and 0

S 2

mB

4 (r )

; along P S

Since, N S|B | |B |

S

PO

2BS BNB

m–m

N

(r + )(r– )

r

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0N S 2 2

m mB B B

4 ( r ) ( r )

2 20 0

2 2 2 2 2

m m( r ) ( r ) 4r

4 4( r ) ( r )

Since M = m 2 (magnetic dipole moment of the bar magnet)

0

2 2 2

2MrB ' along M

4 ( r )

NEUTRAL /NULL POINTS

When we trace magnetic lines of force around a magnet

using a compass needle, what we obtain is the resultant of the

magnetic field of magnet and that of the earth. As earth’s field is

fixed, the resultant field would depend on the direction in which

the magnet is placed. In the plot of the resultant field, we come

across points at which field (B) due to the magnet becomes

equal and opposite to the horizontal component (BH) of earth’s

field i.e. B = BH. Therefore, the net magnetic field at these points

will be zero. These points where net magnetic field due to the

magnet and magnetic field of the earth is zero are called neutral

points. A small compass needle placed at a neutral point shall

experience no force/ torque. Therefore it can set itself in any

direction, which maybe different from the usual N-S direction.

We can show that

When a magnet is placed with its north pole towards

geographic north i.e. in N-S configuration, neutral points lie on

the magnetic axis. At each neutral point,

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0

H2 2 2

2M rB

4 ( r l )

Where, BH is the horizontal component of earth’s magnetic

field.

4. PROCEDURE

a. To locate the mid- point of the paper, fold it from the

middle along the length then unfold it and again fold it along the

breath of the sheet.

b. Stretch the paper on the drawing board and fix it with the

drawing pins.

c. Now place the magnetic compass at the center of the sheet

and rotate the drawing board till needle is along the fold

marking of longer side. Now this fold line will represent the

magnetic meridian. Needle head will point towards GN or MS,

while its tail points towards GS or MN.

d. Move compass on the sheet on the meridian and parallel to

it to find/ draw Earth’s magnetic field magnetic fields (put a dot

on the sheet at the head of the needle, place the compass at the

tail of the needle and again put a pencil dot/ mark on the sheet).

Put arrows on all the lines drawn to obtain BH along the

magnetic meridian.

e. Now place the bar magnet at the centre of paper such that

its north pole of the magnet points towards the geographic north

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of earth (N-N configuration), then put compass needle at the

north pole of the magnet and mark a point on the sheet aty the

head of the needle. Now place the tail of the compass needle at

the previously marked dot and put a pencil dot on the sheet

where the head of the needle is!

f. Repeat the procedure till the compass needle reaches the

other end of the magnet.

g. Join all the points to get a continuous smooth curve.

h. Repeat the procedure from the north pole of the magnet to

draw several magnetic field lines and locate neutral point,

which is obtained on the perpendicular bisector of the magnet.

5.OBSERVATIONS

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From the observation sheet (you need to draw it in the lab)

r 1 = 7.2 cm r2 = 7.2 cm , so r = 7.2 cm

6. CALCULATIONS

For the neutral points on magnetic axis line

HB B

60

2 2 2

2M r25.2 10

4 ( r l )

27 6

2 2 2 8

2M 2.6 1010 25.2 10

(7.2 2.6 ) 10

6

225.2 10 9.8 9.8 4.6 4.6M 0.0984 Am

2 .26

20.0984 Am

7. RESULT

(a) Magnetic field lines corresponding to BH are uniform and

parallel to magnetic meridian.

(b) Magnetic field lines are as expected. The neutral points are

obtained on the magnetic axis.

The magnetic moment of the bar magnet is 0.0984 Am2.

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8. Precautions: — (a) Magnetic meridian should be drawn very

carefully.

(b) Observation sheet on the board should be held taut with the

help of drawing board pins.

(c)Sufficient number of magnetic field should be drawn to

narrow down the position of the neutral points.

9. Bibliography

1. Concepts Of Physics by by H.C. Verma

2. NCERT

3. University Physics.

Note: — You need to submit your own observation sheets. Values for

r1 & r2 can be different for different students as magnets issued may

have different pole strengths…

Note: — Hand written Investigatory Project Report should be submitted.

Work should be neat and clean. Avoid unnecessary fancy decoration of

the project report.

Note: — Learn theory, working and related viva for board practical

examination.

Wish you all the best.

Raj Kumar Parashari

Head Science , JPHS, Jaipur

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Additional content for viva ----

VARIATION OF EARTH’S MAGNETIC FIELD

(a) Global variation (i.e. from place to place)

At about 30000 km above the surface of earth, the earth’s field falls below 610

T. Beyond this height, solar wind disturbs the dipole pattern. The solar wind

consists of streams of charged particles get trapped near the magnetic poles of

earth. They ionize the atmosphere above these poles causing a spectacular display

of light called as Aurora. Magnetic maps showing the variation of magnetic

elements from place to place have been drawn.

The lines joining places of equal declination are called isogonic lines.

The lines joining places of zero declination are called agonic lines.

The lines joining places of equal dip inclination are called isoclinic lines.

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The lines joining places of zero dip inclination are called aclinic lines.

The lines joining places of equal values of horizontal component (H) are

called iso-dynamic lines.

(b) Temporal Variation. (i.e. from time to time) The magnetic field of earth is

found to change with time. These changes may be characterized as short term and

long term changes.

In short term changes, the magnetic poles of earth Sm and Nm keep on

shifting their position. For eg- magnetic south pole has been found to move in

north –westerly direction at a rate of 17 cm per year

(https://www.sciencealert.com/here-s-why-the-north-pole-is-slowly-moving-

towards-london).

The long term changes are on geological time scale 510 to

610 years. It

appears that the direction of earth’s magnetic field has reversed itself every

million year or so. It is believed that once in a million years or so, the currents in

the earth’s core slow down, come to halt and then pick up in the reverse direction.

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SCHOOL NAME SCHOOL NAME SCHOOL NAME - ammhu.com · Aim/ Objective 2. Apparatus Required 3. Theory 4. Procedure 5. Observation 6. Calculation 7. Result 8. Precautions 9. Bibliography