X
Class
CBSE-i
Science
UNIT
-2
PHYSICS : MAGNETISM
CHEMISTRY : METALS
BIOLOGY : CONTROL AND COORDINATION
Shiksha Kendra, 2, Community Centre, Preet Vihar,
Delhi-110 092 India
CBSE-i
Science
PHYSICS : MAGNETISM
CHEMISTRY : METALS
BIOLOGY : CONTROL AND COORDINATION
UNIT
-2
X
Class
Shiksha Kendra, 2, Community Centre, Preet Vihar, Delhi-110 092 India
The CBSE-International is grateful for permission to reproduce and/or
translate copyright material used in this publication.
The
acknowledgements have been included wherever appropriate and
sources from where the material has been taken duly mentioned. In
case anything has been missed out, the Board will be pleased to rectify
the error at the earliest possible opportunity.
All Rights of these documents are reserved. No part of this publication
may be reproduced, printed or transmitted in any form without the
prior permission of the CBSE-i. This material is meant for the use of
schools who are a part of the CBSE-International only.
PREFACE
The Curriculum initiated by Central Board of Secondary Education -International (CBSE-i) is a progressive step in making
the educational content and methodology more sensitive and responsive to the global needs. It signifies the emergence of a
fresh thought process in imparting a curriculum which would restore the independence of the learner to pursue the
learning process in harmony with the existing personal, social and cultural ethos.
The Central Board of Secondary Education has been providing support to the academic needs of the learners worldwide. It
has about 11500 schools affiliated to it and over 158 schools situated in more than 23 countries. The Board has always been
conscious of the varying needs of the learners in countries abroad and has been working towards contextualizing certain
elements of the learning process to the physical, geographical, social and cultural environment in which they are engaged.
The International Curriculum being designed by CBSE-i, has been visualized and developed with these requirements in
view.
The nucleus of the entire process of constructing the curricular structure is the learner. The objective of the curriculum is to
nurture the independence of the learner, given the fact that every learner is unique. The learner has to understand,
appreciate, protect and build on values, beliefs and traditional wisdom, make the necessary modifications, improvisations
and additions wherever and whenever necessary.
The recent scientific and technological advances have thrown open the gateways of knowledge at an astonishing pace. The
speed and methods of assimilating knowledge have put forth many challenges to the educators, forcing them to rethink
their approaches for knowledge processing by their learners. In this context, it has become imperative for them to
incorporate those skills which will enable the young learners to become 'life long learners'. The ability to stay current, to
upgrade skills with emerging technologies, to understand the nuances involved in change management and the relevant
life skills have to be a part of the learning domains of the global learners. The CBSE-i curriculum has taken cognizance of
these requirements.
The CBSE-i aims to carry forward the basic strength of the Indian system of education while promoting critical and
creative thinking skills, effective communication skills, interpersonal and collaborative skills along with information and
media skills. There is an inbuilt flexibility in the curriculum, as it provides a foundation and an extension curriculum, in all
subject areas to cater to the different pace of learners.
The CBSE has introduced the CBSE-i curriculum in schools affiliated to CBSE at the international level in 2010 and is now
introducing it to other affiliated schools who meet the requirements for introducing this curriculum. The focus of CBSE-i is
to ensure that the learner is stress-free and committed to active learning. The learner would be evaluated on a continuous
and comprehensive basis consequent to the mutual interactions between the teacher and the learner. There are some nonevaluative components in the curriculum which would be commented upon by the teachers and the school. The objective
of this part or the core of the curriculum is to scaffold the learning experiences and to relate tacit knowledge with formal
knowledge. This would involve trans-disciplinary linkages that would form the core of the learning process. Perspectives,
SEWA (Social Empowerment through Work and Action), Life Skills and Research would be the constituents of this 'Core'.
The Core skills are the most significant aspects of a learner's holistic growth and learning curve.
The International Curriculum has been designed keeping in view the foundations of the National Curricular Framework
(NCF 2005) NCERT and the experience gathered by the Board over the last seven decades in imparting effective learning to
millions of learners, many of whom are now global citizens.
The Board does not interpret this development as an alternative to other curricula existing at the international level, but as
an exercise in providing the much needed Indian leadership for global education at the school level. The International
Curriculum would evolve on its own, building on learning experiences inside the classroom over a period of time. The
Board while addressing the issues of empowerment with the help of the schools' administering this system strongly
recommends that practicing teachers become skillful learners on their own and also transfer their learning experiences to
their peers through the interactive platforms provided by the Board.
I profusely thank Shri G. Balasubramanian, former Director (Academics), CBSE, Ms. Abha Adams and her team and Dr.
Sadhana Parashar, Head (Innovations and Research) CBSE along with other Education Officers involved in the
development and implementation of this material.
The CBSE-i website has already started enabling all stakeholders to participate in this initiative through the discussion
forums provided on the portal. Any further suggestions are welcome.
Vineet Joshi
Chairman
ACKNOWLEDGEMENTS
Advisory
Shri Vineet Joshi, Chairman, CBSE
Shri Shashi Bhushan, Director(Academic), CBSE
Ideators
Ms. Aditi Misra
Ms. Amita Mishra
Ms. Anita Sharma
Ms. Anita Makkar
Dr. Anju Srivastava
Ms. Anuradha Sen
Ms. Archana Sagar
Ms. Geeta Varshney
Ms. Guneet Ohri
Dr. Indu Khetrapal
Conceptual Framework
Shri G. Balasubramanian, Former Director (Acad), CBSE
Ms. Abha Adams, Consultant, Step-by-Step School, Noida
Dr. Sadhana Parashar, Head (I & R),CBSE
Ms. Jaishree Srivastava
Dr. Kamla Menon
Dr. Meena Dhami
Ms. Neelima Sharma
Dr. N. K. Sehgal
Dr. Rajesh Hassija
Ms. Rupa Chakravarty
Ms. Sarita Manuja
Ms. Seema Rawat
Dr. Uma Chaudhry
Material Production Groups: Classes IX-X
English :
Ms. Sarita Manuja
Ms. Renu Anand
Ms. Gayatri Khanna
Ms. P. Rajeshwary
Ms. Neha Sharma
Ms. Sarabjit Kaur
Ms. Ruchika Sachdev
Geography:
Ms. Deepa Kapoor
Ms. Bharti Dave
Ms. Bhagirathi
Ms. Archana Sagar
Ms. Manjari Rattan
Mathematics :
Dr. K.P. Chinda
Mr. J.C. Nijhawan
Ms. Rashmi Kathuria
Ms. Reemu Verma
Science :
Ms. Charu Maini
Ms. S. Anjum
Ms. Meenambika Menon
Ms. Novita Chopra
Ms. Neeta Rastogi
Ms. Pooja Sareen
Political Science:
Ms. Sharmila Bakshi
Ms. Srelekha Mukherjee
Economics:
Ms. Mridula Pant
Mr. Pankaj Bhanwani
Ms. Ambica Gulati
History :
Ms. Jayshree Srivastava
Ms. M. Bose
Ms. A. Venkatachalam
Ms. Smita Bhattacharya
Material Production Groups: Classes VI-VIII
English :
Ms. Rachna Pandit
Ms. Neha Sharma
Ms. Sonia Jain
Ms. Dipinder Kaur
Ms. Sarita Ahuja
Science :
Dr. Meena Dhami
Mr. Saroj Kumar
Ms. Rashmi Ramsinghaney
Ms. Seema kapoor
Ms. Priyanka Sen
Dr. Kavita Khanna
Ms. Keya Gupta
Mathematics :
Ms. Seema Rawat
Ms. N. Vidya
Ms. Mamta Goyal
Ms. Chhavi Raheja
Political Science:
Ms. Kanu Chopra
Ms. Shilpi Anand
Geography:
Ms. Suparna Sharma
Ms. Leela Grewal
History :
Ms. Leeza Dutta
Ms. Kalpana Pant
Material Production Group: Classes I-V
Dr. Indu Khetarpal
Ms. Rupa Chakravarty
Ms. Anita Makkar
Ms. Nandita Mathur
Ms. Vandana Kumar
Ms. Anuradha Mathur
Ms. Kalpana Mattoo
Ms. Seema Chowdhary
Ms. Anju Chauhan
Ms. Savinder Kaur Rooprai
Ms. Monika Thakur
Ms. Ruba Chakarvarty
Ms. Deepti Verma
Ms. Seema Choudhary
Mr. Bijo Thomas
Ms. Mahua Bhattacharya
Ms. Ritu Batra
Ms. Kalyani Voleti
Coordinators:
Dr. Sadhana Parashar,
Ms. Sugandh Sharma,
Dr. Srijata Das,
Dr. Rashmi Sethi,
Head (I and R)
E O (Com)
E O (Maths)
E O (Science)
Shri R. P. Sharma, Consultant Ms. Ritu Narang, RO (Innovation) Ms. Sindhu Saxena, R O (Tech) Shri Al Hilal Ahmed, AEO
Ms. Seema Lakra, S O
Ms. Preeti Hans, Proof Reader
Content
PHYSICS
1.
SYLLABUS COVERAGE - Physics
3
Core
2
2.
SCOPE DUCUMENT - Physics
4
2
Learning Outcomes
Cross Curricular links
2
3.
Teacher Student Activities - Physics
5
4.
LESSON TEMPLATES - Physics
6
5.
Rubrics Of Assessment For Learning - Physics
34
CHEMISTRY
5.
SYLLABUS COVERAGE - Chemistry
37
2
Core And Extension
6.
SCOPE DUCUMENT - Chemistry
38
2
Learning Outcomes
Cross Curricular links
2
7.
LESSON TEMPLATES - Chemistry
40
8.
Rubrics Of Assessment For Learning - Chemistry
136
BIOLOGY
9.
SYLLABUS COVERAGE - Biology
139
2
Core And Extension
10.
SCOPE DUCUMENT - Biology
140
2
Learning Outcomes
2
Cross Curricular links
11.
LESSON TEMPLATES - Biology
144
Physics
Unit 2
MAGNETISM
Physics
Syllabus Coverage
Unit 2 - MAGNETISM
Core
S
Y
L
2
Magnets and Magnetic Materials
2
Properties of magnet
2
Difference between permanent magnets and electromagnets
L
2
Magnetic field around a current carrying conductor
A
2
Maxwell's right hand grip rule
B
2
Uses of magnets and electromagnets
U
S
2
Force on a current carrying conductor placed in a magnetic field
2
Fleming's left hand rule
2
Function and working of Electric motor
SCIENCE UNIT-2
3
PHYSICS
SCOPE DOCUMENT
Learning outcomes
At the end of this unit, students should be able to
Describe and identify magnets and magnetic materials.
Describe properties of magnet.
Differentiate between permanent magnet and an electromagnet.
Describe magnetic field around a current carrying wire and a solenoid.
Explain uses of magnets and electromagnets.
Understand and describe that a current carrying conductor when placed inside a
magnetic field experiences a force.
Describe factors that affect the force on a current carrying conductor placed in a
magnetic field.
State and explain Fleming's Left Hand Rule.
Describe the construction and working of an electric motor.
Cross curricular links
History - History of magnets and magnetism.
Geography - Uses of compass needle and magnets in finding directions.
Biology - Uses of magnetism in the field of medicine.
PHYSICS
4
SCIENCE UNIT-2
Steps to be
followed
Teacher's Activity
Student's Activity
1.
SYLLABUS COVERAGE - Physics Page no- Core and Extension
2.
SCOPE DOCUMENT- Physics
Page no
C
Learning Objectives
C
Cross Curricular Links
C
Suggested Activities
3.
LESSON TEMPLATE- Physics
Page no
4.
S t u d e n t - T e a c h e r S u p p o r t Page number
Material-Physics
5.
Rubrics of Assessment- Physics
6.
S Y L L A B U S C O V E R A G E - Page no
Chemistry
Core and Extension
SCOPE DOCUMENT- Chemistry Page no
C
Learning Objectives
C
Cross Curricular Links
C
Suggested Activities
7.
Page no
8.
LESSON TEMPLATE- Chemistry
9.
S t u d e n t - T e a c h e r S u p p o r t Page no Material- Chemistry
10.
Rubrics of Assessment-Chemistry Page no -
11.
SYLLABUS COVERAGE- Biology Page no Core and Extension
12.
SCOPE DOCUMENT- Biology
Page noC
Learning Objectives
C
Cross Curricular Links
C
Suggested Activities
13.
LESSON TEMPLATE- Biology
Page no -
14.
S t u d e n t - T e a c h e r S u p p o r t Page no -
15.
Material- Biology
Rubrics of Assessment-Biology
SCIENCE UNIT-2
5
Page no-
Page no -
PHYSICS
LESSON TEMPLATE
Steps to be
followed
Pre content
Warming Up
Activity
Content
Development
Student Teacher
Material
1. Magnetic
Material
2. Magnetic
Domain
2.1 Types of
Magnet
Teacher's Activity
Student's Activity
Teacher may start the class by Students will understand the
discussing the devices which rely role of magnets for the
on magnets for their working.
working of some devices .
T e a c h e r m a y e x p l a i n t h e Students will try to answer
properties of magnetic materials t h e q u e s t i o n s a n d
with the help of activity 1.
differentiate between
magnetic and non magnetic
materials.
Teacher may explain the reason for Students will understand the
the property of attraction of w o r k i n g a n d t y p e s o f
magnets using Domain Theory. magnets through activities.
He/She may explain the different
types of magnets with the help of
activities and questions.
Activity 2 and 2.1
3. Properties of a
magnet
Teacher may demonstrate the
properties of a magnet With the
help of Experiments 3.1,3.2,3.3 and
3.4. He/She may also explain
earth's magnetism.
Students will understand the
properties of a magnet like, it
points towards north south
direction etc. with the help of
experiments.They will also
gain the knowledge about
earth's magnetism.
4.
Electromagnetism
Teacher may explain the term
electromagnetism with the help of
an activity. Teacher may
demonstrate the making of an
electromagnet and determining
the direction of the field around a
current carrying conductor using
the Right Hand Grip rule.
Students will understand the
term electromagnetism.
They will learn how to make
an electromagnet and find
the direction of magnetic
field around a current
carrying conductor.
4.1 Electromagnet
4.2 Maxwell's
RIGHT Hand
Grip Rule
PHYSICS
6
SCIENCE UNIT-2
Activity 4 and 4.1
http://www.metacafe.com/watc
h/1097288/build_an_electromag
net/
5. Uses of
Magnets
Teacher may explain the uses of Students will gain the
magnets using daily life examples. knowledge about the various
uses of magnets
Read more: Everyday Uses of
Magnets | eHow.com
http://www.ehow.com/facts_5314
850_everyday-usesmagnets.html#ixzz1GC0tXgZr
6. Force
Experienced
by a current
carrying
conductor
placed in a
magnetic field.
Teacher may explain that a current Students will understand
carrying conductor experiences a the concept through
force when kept in a magnetic field demonstrations.
with the help of a Java Applet and
an activity (activity 6). Teacher
may also explain the use of
Fleming's Left Hand Rule.
6.1 Flemings Left
Hand Rule
http://www.youtube.com/watch?
v=14SmN_7EcGY
7. Construction
and Working of
an Electric Motor
Teacher may use the PowerPoint Students will understand the
Presentation provided herewith to working and usage of electric
explain the construction and motor.
working of an electric motor.
8. Revision
T e a c h e r m a y a s s e s s t h e Students will attempt the
understanding of the unit by revision worksheets given to
using the given worksheets
them.
8.1 Worksheet 1
8.2 Worksheet 2
9. Projects
SCIENCE UNIT-2
Teacher may ask the students to Students will work on the
work on the given projects given projects.
individually or in groups
7
PHYSICS
TEACHER'S NOTES
FLOW CHART FOR MAGNETISM
Warm Up Activity
Activity on Properties of magnetic material
Questions for discussion
Activities on Magnetic Domain
Questions for Discussion
Hands on Experiments on properties
Questions for Discussion
Of Magnets
Demonstration on Electromagnetism
Questions for Discussion
Right Hand Grip rule
Model Making
Electromagnet
Explanation of uses of magnet
Suggestive Links
With the help of daily life Examples
Demonstration of Force on a current
Carrying conductor using Java Applet
Fleming's left hand rule
Questions
Demo of working of an electric motor
Using the given PPT
Project
Summative Assessment Sheets
PHYSICS
8
SCIENCE UNIT-2
WARM UP ACTIVITY;
THE MYSTERY OF MAGNETISM
Learning objective Identify a number of common items that rely on magnetism to work.
Each time we turn on a light, listen to our stereo, fly in an airplane, or watch TV, we are
depending on the principles of magnetism to work for us. Take a look at the pictures
below. Identify what these pictures have to do with magnetism?
Magnetic Particle Inspection Unit-
Hydroelectric Dam
Airplane Navigational Panel
Fan
Video Cassette Tape
Can you imagine how your life might be affected without these? What do you think
magnetism has to do with each of these things? Think about these questions as you
explore these materials on magnetism.
SCIENCE UNIT-2
9
PHYSICS
ACTIVITY 1 : MAGNETIC MATERIAL
Learning Objective:
Students will be able to identify what materials are magnetic and explain why we think
they are magnetic.
Material required: Magnet, pencil, ball, keys, glass prism, scissors etc.
Teacher will slide the magnet over the collected material and students will note down
the observations and answer the following questions.
Questions for discussion:
What conclusions can you draw about the items given in the activity?
What is a magnet?
How do you think something becomes a magnet?
What do you think is different about the items that get attracted to a magnet and items
that do not?
What do you think about the origin of magnetism?
How small can a magnet be?
PHYSICS
10
SCIENCE UNIT-2
Just like when the Greeks of the old times discovered the first naturally occurring
magnetic stones, or natural magnets, you have been observing a property of matter
called magnetism. Magnetism is observing the effects of the force of attraction or
repulsion in and around a magnet. Magnetism is relevant for all materials but it is
usually at such low levels that it is not easily appreciated. Certain materials such as
magnetite, iron, steel, nickel, cobalt and alloys of rare earth elements, exhibit
magnetism at levels that are easily detectable.
We usually think of a magnet as any piece of material that has the property of attracting
iron (or steel). Magnetite, also known as lodestone, is a naturally occurring rock that is a
magnet. This natural magnet was first discovered in a region known as magnesia and
was named after the area in which it was discovered. Magnetism may be naturally
present in a material or the material may be artificially magnetized by various methods.
Magnets may be permanent or temporary. After being magnetized, a permanent
magnet will retain the properties of magnetism indefinitely. A temporary magnet is a
magnet made of soft iron that is usually easy to magnetize; however, temporary
magnets lose most of their magnetic properties when the magnetizing cause is
discontinued. Permanent magnets are usually more difficult to magnetize, but they
remain magnetized. Materials which can be easily magnetized are called
ferromagnetic materials. We will talk more about making a magnet later on.
A magnet can be cut into smaller and smaller pieces indefinitely. However, we find that
even the smallest piece still acts as a small magnet. Thus, the cause of magnetism must
be from a property of the smallest particles of the material, the atoms. So what is it about
the atoms of magnets, or objects that can be magnetized (ferromagnetic materials), that
is different from the atoms of other material? For example, why is it that copper keys or
aluminum cans cannot be magnetized?
SCIENCE UNIT-2
11
PHYSICS
ACTIVITY 2 : MAGNETIC DOMAIN
Learning Objective:
Student will be able to define a magnetic domain.
Explain one way of magnetizing an object.
Material required; Magnet, a piece of metal {paper clip}
Teacher rubs the piece of given metal with a strong magnet repetitively in one sense
only and demonstrates the magnetic properties developed in the metal piece. Teacher
can use following diagrams to explain magnetic domains.
Step 1
Click and drag the magnet across the metallic strip.
The arrows represent the alignment of the atoms in the metallic strip.
Step 2
A magnetic domain is region in which the magnetic fields of atoms are grouped
together and aligned. In the experiment above, the magnetic domains are indicated by
the arrows in the metal material. You can think of magnetic domains as miniature
magnets within a material. In an unmagnetized object, like the initial piece of metal in
our experiment, all the magnetic domains are pointing in different directions. But,
when the metal became magnetized, which is what happens when it is rubbed with a
strong magnet, all like magnetic poles get lined up and point in the same direction. The
metal became a magnet. It would quickly become unmagnetized when its magnetic
domains returned to a random order. The metal in our experiment is a soft
ferromagnetic material, which means that it is easily magnetized but may not retain its
magnetism very long.
PHYSICS
12
SCIENCE UNIT-2
Questions for discussion:
What happened to the piece of metal when you rubbed a strong magnet across it the
first time? The second time?
What do the arrows in the material represent?
Why do they become lined up when the magnet is brought in contact with the metal?
If you wanted to turn a paper clip into a magnet, how do you think you could do it?
We can turn a paper clip into a magnet by rubbing a strong magnet several times over
the surface of the paper clip. The more you drag the magnet over the paper clip, the
stronger the paper clip will become magnetized. The same thing happened with the
metal in the experiment. When we rubbed the magnet over the surface of the metal,
some of the magnetic domains aligned and the metal became partially magnetized.
When we rubbed the magnet over the metal a second time, more of the magnetic
domains became aligned and the metal became a stronger magnet.
In ferromagnetic materials, the magnetic moments of a relatively large number of
atoms are aligned parallel to each other to create areas of strong magnetization within
the material. These areas, which are approximately a millimeter in size, contain billions
of aligned atoms and are called magnetic domains. Magnetic domains are always
present in ferromagnetic materials due to the way the atoms bond to form the material.
However, when a ferromagnetic material is in the unmagnetized condition, the
magnetic domains are randomly oriented so that the magnetic field strength in the
piece of material is zero.
In the unmagnetized condition, the material will be attracted to a magnet but will not
act as a magnet. That is to say, two unmagnetized pieces of ferromagnetic material will
not be attracted to each other. When a ferromagnetic material is magnetized, the
magnetic domains align parallel to each other to produce a large net field strength in
the material and the material becomes magnetic.
SCIENCE UNIT-2
13
PHYSICS
ACTIVITY 2.1 : TYPES OF MAGNET
Learning Objective:
Student will be able to do the following:
Explain the differences between a permanent magnet and a temporary magnet.
Explain why some materials have magnetic properties only when a permanent magnet
is near them.
Material required:
Strong magnet, number of paper clips.
Teacher will demonstrate how a magnet attracts a
paper clip, which further attracts more clips. Students
will answer the following questions.
Questions for discussion:
What is happening in this experiment?
What conclusions can you draw about magnets and magnetism from this experiment?
We have noted, in previous discussions that magnets can be permanent or temporary.
A permanent magnet is more difficult to magnetize but will retain the properties of
magnetism indefinitely. A temporary magnet is generally made of soft iron and will
remain magnetized only as long as the magnetizing cause is present. From previous
experiments you saw how the difference in magnetized and unmagnetized material
depends on the motion and arrangement of the material's molecules. Bringing a
ferromagnetic object, like a nail, into the magnetic field of a strong magnet, can cause
the molecules of the iron material to line up and the nail to become a temporary magnet.
As long as it is in the magnetic field of the bar magnet, the nail acts like a magnet and
picks up other ferromagnetic materials. In this case it is the paper clip. Then, the paper
clip becomes a magnet and can pick up another paper clip, and so forth.
PHYSICS
14
SCIENCE UNIT-2
ACTIVITY 3 : PROPERTIES OF MAGNETS
Learning Objective:
Student will be able to
Explain what a compass is and how it is affected by a magnet.
Understand how a compass helps us to navigate on the earth.
Explain how two ends of the magnet behave.
Material required : Two Ordinary bar magnets, regular compass
Experiment 3.1 : Students will tie a bar magnet with a thread, tied at the centre and
suspend it freely with the help of a support.
Experiment 3.2 : Students will move the given two bar magnets close to each other,
keeping the North pole of one pointing towards South pole of the other.
Experiment 3.3 : Students will move the given two bar magnets close to each other,
keeping the South pole of one pointing towards South pole of the other.
Experiment 3.4 : Teacher will tell the students to circle the compass needle around the bar
magnet and record / mark the direction of the compass needle at all
points. Alternatively students can be told to place a bar magnet on a
cardboard, sprinkle iron fillings around it and tap the board lightly.
SCIENCE UNIT-2
15
PHYSICS
Questions for discussion:
What happened to the blue pole of the compass arrow when it was brought close to the
north pole of the magnet?
What happened to the blue pole of the compass arrow when it was brought close to the
south pole of the magnet?
What is a compass and what direction does it always point?
What would you expect to happen if a magnet is suspended by a string and allowed to
hang freely?
From your observations, what can you conclude about the earth's magnetic properties?
What we have been observing is the behavior of the north and south poles of a magnet.
One end of any bar magnet will always want to point north if it is freely suspended. This
is called the north-seeking pole of the magnet, or simply the north pole. The opposite
end is called the south pole. The needle of a compass is itself a magnet, and thus the
north pole of the magnet always points north, except when it is near a strong magnet. In
Experiment 1, when we bring the compass near a strong bar magnet, the needle of the
compass points in the direction of the south pole of the bar magnet. When we take the
compass away from the bar magnet, it again points north. So, we can conclude that the
north end of a compass is attracted to the south end of a magnet.
This can be a little confusing since it would
seem that what we call the North Pole of the
Earth is actually its magnetically south
pole. Remember that a compass is a magnet
and the north pole of a magnet is attracted
to the south pole of a magnet. This situation
is also seen in Experiment 1 & 2. In
Experiment 2, when we move the north
pole of a magnet toward the south pole of
the other magnet, the two magnets attract.
However, in Experiment 3, when we move
the south pole of a magnet toward the
south pole of another magnet, the two
magnets repel each other and we cannot
move them together. The rule for magnetic
poles is that like poles repel each other and unlike poles attract each other.
PHYSICS
16
SCIENCE UNIT-2
Since the north seeking pole of a compass always wants to point north, then the
compass could be useful in helping us navigate. With a compass we can always tell
which direction is north and if we know north, then we know all of the other directions.
A compass and a map are essential tools when hiking in the woods. Since the north
seeking pole of the compass needle is always attracted to the north, then the earth must
be like a huge magnet with a magnetic pole at each end. This is exactly the case but
magnetic north is slightly different from the north defined for the axis of rotation of the
earth. Scientists believe that the movement of the Earth's liquid iron core and other
things are responsible for the magnetic field around the earth.
SCIENCE UNIT-2
17
PHYSICS
ACTIVITY 4 : ELECTRO MAGNETISM
After reading this section, students will be able to do the following:
Describe how a magnetic field is created.
Explain how the electromagnet and the solenoid work together.
Material Required; simple compass and piece of wire connected to a battery & on-off
switch.
Teacher will demonstrate that initially the compass will point North but when current
passes through the wire kept nearby and perpendicular to the plane containing the
compass, the needle deflects. When the direction of flow of current is reversed needle
deflects in opposite direction.
Questions for discussion;
What happens to the compass needle as the compass moves around the wire carrying
electrical current?
Why do you think this happens?
We can conclude from this experiment that an electric current causes a magnetic field
around it just like a magnet causes a magnetic field. When you moved the compass near
a bar magnet, the needle pointed toward the magnet's magnetic field and not toward
the north. When you put the compass near the electrical wire with current flowing
through it, the compass did not point north; instead, the compass needle pointed in the
direction of the current's magnetic field.
PHYSICS
18
SCIENCE UNIT-2
Historical Background:
In 1820, a Danish scientist named Hans Oersted
discovered that a magnetic compass could be deflected
from its resting position if a wire, carrying electric
current, was placed near the compass. This deflection of
the compass only occurred when current was flowing in
the wire. When current was stopped, the compass
returned to its resting position.
This graphic seems to indicate that any wire in which an electric current is flowing is
surrounded by an invisible force field called a magnetic field. For this reason, any time
we deal with current flowing in a circuit, we must also consider the effects of this
magnetic field. We have all probably had experiences with magnets at one time or
another. Magnets can easily attract certain types of material like iron but almost
nothing else.
The term electromagnetism is defined as the production of a magnetic field by current
flowing in a conductor. We will need to understand electromagnetism in greater detail
to understand how it can be used to do work.
Coiling a current-carrying conductor around a core material that can be easily
magnetized, such as iron, can form an electromagnet. The magnetic field will be
concentrated in the core. This arrangement is put to use in a device called a solenoid.
The more turns we wrap on this core, the stronger the electromagnet and the stronger
the magnetic lines of force become.
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ACTIVITY 4.1 : ELECTRO MAGNET
Learning Objectives : Students will be able to understand that
Wrapping the wire around a piece of iron creates a electromagnet.
Material required : One iron nail fifteen centimeters (6 in) long, Three meters (10 ft) of
22 gauge insulated, stranded copper wire, One or more D-cell batteries and a pair of wire
strippers
Teacher's instructions : Use a pair of wire strippers to remove a few centimeters of
insulation from each end of the wire. Neatly wrap the wire around the nail. The more wire
you wrap around the nail, the stronger your electromagnet will be. Make certain that you
leave enough of the wire unwound so that you can attach the battery.
When you wrap the wire around the nail, make certain that you wrap the wire all in
one direction. You need to do this because the direction of a magnet field depends
on the direction of the electric current creating it. If you wrap some of the wire
around the nail in one direction and some of the wire in the other direction, the
magnetic fields from the different sections fight each other and cancel out, reducing
the strength of your magnet.
Attach one end of the wire to the positive terminal of the battery and the other end of
the wire to the negative terminal of the battery. If all has gone well, your
electromagnet is now working!
Try experimenting with more number of turns of wire, increasing the current or
using different cores of varied thickness.
Caution! Too much current can be dangerous! As electricity passes through a wire,
some energy is lost as heat. The more current that flows through a wire, the more
heat is generated. If you double the current passing through a wire, the heat
generated will increase 4 times!
http://www.metacafe.com/watch/1097288/build_an_electromagnet/
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An electromagnet, which behaves just like a regular permanent bar magnet when
the current is flowing. Notice that all of the lines of force pass through the center of
the core material, regardless of how they extend outside the coil of wire. The
direction of magnetic polarity is determined by the direction of current flowing in
the coil of wire. The direction that the wire is coiled around the core also determines
the direction of magnetic polarity. This is important to know if we want to use the
electromagnet to apply a force to another material.
Review
A magnetic field is generated whatever an electric current flows through a
conductor.
The magnetic field around the conductor flows in closed loops.
Wrapping the wire into a coil creates an electromagnet.
Wrapping the wire around a piece of iron creates a solenoid.
Remember that electrons always have a negative electrostatic field surrounding
them. When energy, from a power source, such as a battery, is applied to a circuit,
making the electrons flow through a conductor, a new type of field is developed
around the wire. This is called an magnetic field.
We can see in the diagram below, the magnetic field that surrounds a currentcarrying conductor is made up of concentric lines of force. The strength of these
circular lines of force gets progressively smaller the further away from the
conductor we get. Also, if a stronger current is made to flow through the conductor,
the magnetic lines of force become stronger. As a matter of fact, we can say that the
strength of the magnetic field is directly proportional to the current that flows
through the conductor.
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The term magnetic field intensity is used to describe the strength of the magnetic
field. From now on we will use this new term to describe this field that is developed
around a conductor that is carrying electrical current.
4.2
Maxwell's Right Hand Grip Rule
We have observed that this magnetic force field is a result of current flowing in a
conductor. We have also shown that the pattern of this field is circular in shape.
What we do not yet know is what direction the circular field is in.
A number of different rules have been developed to help determine the direction of
the magnetic field relative to the current. "The right-hand rule" is the simplest to
remember and can be used to determine the direction of the magnetic field around a
current carrying conductor. With this rule, when the thumb of the right-hand is
pointing in the direction of current flow, the sense of curling, of the fingers will be
along the direction of the magnetic field.
Review
Field intensity is a term used to describe the strength of the magnetic field.
Field intensity is determined by the amount of electrical current flowing in the wire.
The right-hand rule can be used to describe the direction of the magnetic field.
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ACTIVITY 5 : USES OF MAGNETS
Magnets are also used to design electric motors and generators. Without these
electric motors and generators we would not have telephones, electric lights,
electric heaters, television, or computers.
1.
Sometimes magnets are used to sort magnetic and non-magnetic materials.
Food manufactures use magnets to keep small metal filings from getting into food.
Candy and coke venders use magnets to separate coins from slugs that are put into
their machines.
2.
At home, we use magnets to hold things up or to pick up small things: Some
examples of this are:
sewing pins
electric can openers
Magnets can hold things to the refrigerator.
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3.
Magnets are also used in compasses to show attraction and repulsion. Magnetized
compasses are used to detect underground metal pipes. A magnetic compass helps
us in finding direction also.
4.
Magnets are a simple, reliable way to latch doors on refrigerators and cabinets.
5.
From tiny ear buds to stadium PA systems, every speaker has a magnet in it. The
stronger the magnet, the better the sound quality.
6.
DC motors have a set of permanent magnets and electromagnets inside. When
connected to a battery, the electromagnets repel the permanent magnets and make
the motor spin.
7.
Credit cards have a strip of magnetic material on their back side. Account data are
recorded on it in a special, machine-readable format.
8.
According to Chinese inscriptions in 2000 BC, 'lodestones' were used in
acupuncture treatments. Hindu sacred writings also refer to the use of 'lodestones'
in the treatments of disorders. Likewise, the Greeks and the Egyptians also utilized
them to cure various diseases. Ancient physicians described how magnets had the
ability to cure melancholy, arthritis, and baldness.
Nowadays, tectonic magnets are used by many sportsmen to reduce or relieve pain.
They are placed on the innersoles of shoes, and are designed in such a manner that
they would make contact with the acupressure points present on the soles of the
feet. This technique is proven to be helpful for the feet, especially on long walks.
Magnetic mattress pads also provide relaxation to the body, and are very helpful for
insomniacs. Magnetic beds are used to provide easiness to the nervous system,
which may make a person emotionally and physically loosened up. Magnets are
also used in X-Rays, and Magnetic Resonance Imaging (MRI) technology, which
enables one to know how body tissues respond to the magnetic fields.
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9.
Magnets are a very important part of a televisions. The Cathode Ray Tubes (CRT)
consist of an electron gun in their neck, which shoots a stream of electrons on the
screen. Generally, the electrons are released in a straight line, and impact the center
point of the screen. Electromagnets which are present in the tube's neck turn away
the electrons towards the top, bottom, right, or left side of the tube. This process
makes the inside coating of the screen to glow, which enables images and videos to
be shown on the television.
10.
Magnets also play an important role in computer disks which are coated with iron
material that store small magnetic fields in a specific format. Moreover, magnets are
incorporated in computer monitors who work in the same manner as a television.
Video tapes consist of same components along with iron compounds, which enable
the magnetic fields to be stored in a particular fashion on the tape.
11.
Household accessories and items like loudspeakers, home theaters, headphones,
telephone receivers, etc., also include magnets in their mechanism.
12.
Powerful magnets such as conveyor magnets are used in industries to carry out
their manufacturing operations. During the production process, goods are
transferred from one place or process to the other, using conveyor belt systems. This
is usually done in the case of plastic, wood, or food processing. The conveyor
magnets are responsible for removing all metal waste materials from the goods on
the conveyor belt, leaving only the pure needed components for further processing.
The magnet prevents the metal waste from being included in the later processes
such as grinding. In the same manner, magnets are installed in large machinery
which makes their respective operations easy and quick.
13.
Some items that use electromagnets are: Maglev trains, car crushers, scrap metal
sorters, telephones, computers, doorbells, tape recorders etc.
Maglev trains use super conducting magnets in the track and on the underside of
the train to "float" above the track. Maglev trains use magnetic repulsion. Maglev
trains can travel very fast, up to 480 km/h (300 mph). These Maglev trains are being
used in Japan. This train line opened in April 1997. In April of 1999 this train was
clocked at an incredible 343 miles
an hour!
The United States
government has set aside 1 billion
dollars to build a Maglev train.
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An electromagnet is being used to sort metals in a scrap yard.
Electricity is used to make a temporary magnet, called an electromagnet to run a car
crusher. As long as the electric current is on, the iron crane is a magnet and can pick up
ferromagnetic objects. When the electricity is turned off, the magnetizing cause is no longer
present, so the object is not attracted to the iron crane and it falls into the crusher.
Magnets are important components in
most of the things that we use daily. As
technology progresses, there would be
more and more functions and uses of
magnets coming up in various systems
and machinery.
Read more: Everyday Uses of Magnets |
eHow.com
http://www.ehow.com/facts_5314850_everyday-uses
magnets.html#ixzz1GC0tXgZr
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SCIENCE UNIT-2
6.
Force on a current- carrying conductor in a magnetic field
Oersted's experiment shows that a current carrying wire exerts a force on a
magnetic needle and deflects it from its usual north-south position. The reverse
must also be true, which was proved by the French scientist Andre Marie Ampere,
who suggested that a magnet must also exert an equal and opposite force on the
current carrying conductor. The above mentioned concept can be best understood
by way of a demonstration as explained below.
http://www.youtube.com/watch?v=14SmN_7EcGY
ACTIVITY : 6
Demonstration activity to be done by the Teacher
Learning Objectives:
1.
A current carrying conductor experiences a force when placed in a magnetic field.
2.
The direction of force is reversed when the direction of current in the conductor is
reversed.
A small aluminum rod AB (5 cm in length) is connected to the wires and suspended
horizontally as shown in the fig.
A strong horse-shoe magnet is placed in such a way that the magnetic field is
directly upwards and is placed vertically.
The rod AB is connected in series to a battery, a key and a rheostat. Current is
switched on and the rod AB gets displaced.
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Teacher can repeat the experiment by changing the direction of flow of current and
also by reversing the direction of magnetic field. Students can be told to note and
explain why the rod gets displaced in reverse direction in each case.
ACTIVITY 6.1. FLEMING'S LEFT HAND RULE
Fleming's left hand rule helps us to predict the movement of a current carrying
conductor placed in a magnetic field.
According to this rule, extend the thumb, forefinger, and the middle finger of the left
hand in such a way that all the three are mutually perpendicular to each another. If
the forefinger points in the direction of the magnetic field and the middle finger in
the direction of the current, then, the thumb points in the direction of the force
exerted on the conductor.
Devices that use current carrying conductors and magnetic fields include electric
motors, generators, loudspeakers and microphones.
ACTIVITY 7 : ELECTRIC MOTOR
An electric motor is a device which converts electrical energy into mechanical
energy. A common motor works on direct current. So, it is also called DC motor.
Principle
When a rectangular coil carrying current is placed in a magnetic field, a torque acts
on the coil which rotates it continuously.
When the coil rotates, the shaft attached to it also rotates and thus it is able to do
mechanical work.
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Construction and Working - Parts of a DC Motor
Armature
A D.C. motor consists of a rectangular coil made of insulated copper wire wound on
a soft iron core. This coil wound on the soft iron core forms the armature. The coil is
mounted on an axle and is placed between the cylindrical concave poles of a
magnet.
Commutator
A commutator is used to reverse the direction of flow of current. Commutator is a
copper ring split into two parts C1 and C2. The split rings are insulated form each
other and mounted on the axle of the motor. The two ends of the coil are soldered to
these rings. They rotate along with the coil. Commutator rings are connected to a
battery. The wires from the battery are not connected to the rings but to the brushes
which are in contact with the rings.
Brushes
Two small strips of carbon, known as brushes press slightly against the two split
rings, and the split rings rotate between the brushes.
The carbon brushes are connected to a D.C. source.
Working of a DC Motor
When the coil is powered, a magnetic field is generated around the armature. The
left side of the armature is pushed away from the left magnet and drawn towards
the right, causing rotation.
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When the coil turns through 90°, the brushes lose contact with the commutator and
the current stops flowing through the coil.
However the coil keeps turning because of its own momentum.
Now when the coil turns through 180°, the sides get interchanged. As a result the
commutator ring C1is now in contact with brush B2 and commutator ring C2 is in
contact with brush B1. Therefore, the current continues to flow in the same direction.
Refer to ppt 'Magnetic Effects of Current’
The Efficiency of the DC Motor Increases by:
Increasing the number of turns in the coil
Increasing the strength of the current
Increasing the area of cross-section of the coil
Increasing the strength of the radial magnetic field
REVISION
8.1. WORKSHEET 1
Q.1
Name two important properties of a magnet.
Q.2
What is the direction of magnetic field lines inside a magnet?
Q.3
Draw magnetic field lines to depict uniform magnet field.
Q.4
What type of magnetic field lines represent uniform magnetic field?
Q.5
What is the form of magnetic field lines due to a straight current carrying
conductor?
Q.6
Name the rule used to find the direction of magnetic field due to a straight current
carrying conductor.
Q.7
How do we determine the direction fo magnetic field at a point due to a given
source.
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Q.8
Name the unit of magnetic field.
Q.9
What is a solenoid?
Q.10 For what purpose do we apply clock rule (end rule)?
Q.11 What is the effect of inserting a soft iron core inside a current carrying solenoid?
Q.12 What type of core is used to make an electromagnet?
Q.13 What are permanent magnets made of?
Q.14 Why is soft iron not used for making a permanent magnet?
8.2 WORKSHEET 2
1.
2.
3.
If one doubles the number of coils and doubles the voltage applied across a coil,
what would be the increase in magnetic strength?
(a)
It would remain the same, since 2 / 2 = 1
(b)
It would be 4 times as strong, since 2 x 2 = 4
©
You can't increase magnetism by increasing the voltage
Why should the wire around the iron core be insulated?
(a)
So that you don't create a short circuit
(b)
To keep the iron from getting too warm
(c)
To insulate the magnetism
Why does an iron core increase the magnetic field of a coil of wire?
(a)
The iron atoms line up to add to the magnetic field
(b)
Iron attracts things, including magnetic fields
(c)
The iron core actually decreases the field, allowing it to be turned off
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4.
Draw the pattern of the magnetic field produced by electric current flowing through
a straight wire and through a wire coil:
Explain your answer using either the right-hand rule (conventional flow) or the lefthand rule (electron flow).
5.
If an electric current is passed through this wire loop, in which position will it try to
orient itself?
If this experiment is carried out, it may be found that the torque generated is quite
small without resorting to high currents and/or strong magnetic fields. Devise a
way to modify this apparatus so as to generate stronger torques using modest
current levels and ordinary magnets.
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SCIENCE UNIT-2
9.
PROJECTS
Visit www.novitachopra.blogspot.com to further understand the concepts of Lenz
Law and ac generator through Java applets and complete the assignment titled
"Magnetic Effects of Current".
Visit www.physicsmantra.ning.com to learn making of simplest electric dc motor
and generator through videos and submit a working model of dc motor under your
physics project.
Make ppt/brochure/handouts to illustrate the daily life impact of magnetic effects
of current and use of electric motors and generators in domestic affairs
Study the electrical circuit of your house {under parental supervision}, collect data,
draw circuit diagrams and make a presentation on precautions and safety measures
to be taken in domestic electrical circuits and appliances to avoid overloading and
shock.
Research work - visit a hospital / pathology lab or take a virtual tour on the net and
talk to experts to study Magnetic Resonance Imaging {MRI}. Investigate further
how magnetism can be used in medicine
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RUBRICS OF ASSESSMENT FOR LEARNING
Unit 2 - MAGNETISM
Parameter
Learner is able to
Beginning
(1)
Approaching Meeting
(2)
(3)
Exceeding
(4)
Describe and identify magnets
and magnetic materials.
Describe properties of
magnet.
Differentiate between
permanent magnet and
electromagnet.
Describe magnetic field
around a current carrying
wire and a solenoid.
Explain uses of magnets and
electromagnets.
Understand and describe that
a current carrying conductor
when placed inside a
magnetic field experiences a
force.
Describe factors that affect the
force on a current carrying
conductor placed in a
magnetic field.
State and explain Fleming's
left hand rule.
Describe the construction and
working of an electric motor.
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