Magnetic effect of current ppt

1. MAGNETIC EFFECT OF
CURRENT

4. • Oersted discovered that:
The wire carrying current deflected the needle of the magnetic
compass placed near the wire, this effect of current passing through a
wire (conductor) is known as magnetic effect of current.

5. • MAGNETIC FIELD:
The space around the magnet in which the force of attraction or
repletion can be detected.

6. 1)what is a compass needle? What happens when it is brought near a bar
magnet?
A compass needle is a small magnet. When a compass needle is brought
near a bar magnet a compass needle gets deflected.
2)In which direction the ends of a compass needle point? What is north pile
and south pole? Mention 1 property of a magnetic pole.
The ends of a compass needle points towards north, south direction. The
end pointing towards north is know as north pole and the end which is
pointing towards south is know as south pole.
Like poles repel reach other and unlike pole attract each other.
Magnetic poles exist in pairs.

7. 3) Why does a compass needle get deflected when it is brought near a
bar magnet?
A compass needle itself is a small bar magnet, it gets deflected because
it experiences a magnetic force.
• MAGNETIC LINES OF FORCE/ MAGNETIC FIELD LINES:
It is a straight or curved path in the region of magnetic field. It is used
to represent the magnetic field in the given region(or) it is the path
along which a free north poles tends to move if it is free to move.

8. 4)Some iron fillings are sprinkled uniformly around the bar magnet. When
the board is gently tapped. Why do the iron fillings arranged in a pattern.
What does the pattern indicates?
The magnet exerts its influence in the region surrounding it. Therefore, the
iron fillings experience a force. This makes the iron fillings to arrange in a
pattern.
The line along which the iron fillings align themselves represents the
magnetic field lines.
5)mention two methods by which the magnetic field around the bar magnet
can be observed?
1.By drawing, the magnetic field lines using a magnetic compass.
2.Iron fillings near the bar magnet align themselves along the magnetic field
lines.

9. • DIRECTION OF MAGNETIC FIELD:
Magnetic field is a vector quantity. It has both magnitude and direction.
The direction in which the north pole of the magnetic compass moves
in the magnetic field gives the direction of the magnetic field.

10. • Show by means of diagram the magnetic field around a bar magnet:

14. 1. A magnetic lines emerge from the north pole and merge at the
south pole.
2. Outside the magnet the direction of field lines is from north pole to
south pole.
3. Inside the magnet the direction of field lines is from south to north
pole.
4. Thus the magnetic field lines are closed curves.
5. No two magnetic field lines intersect each other.
6. The magnetic lines of force are closely spaced in the region where
the magnetic field is strong.

15. 7) No two magnetic field lines do not cross each other why?
Two magnetic field lines do not cross each other. If they cross it would
mean that at the point of intersection a compass needle would point
towards two direction which is not possible.
8)How can we identify the relative strength of magnetic field? What is
meant by a strong field?
The relative strength of magnetic field is identified by the degree of
closeness of the field lines. The force acting on the pole of another
magnet placed is greater where the field lines are crowded. This is
called as a strong field.

16. 9)What does he arrow in the magnetic field line indicate?
The arrow in the magnetic field lines indicates the direction of the
north pole of the magnetic needle of the compass.
10) A compass needle is placed parallel and over a copper wire caring
current. In which direction the north pole of the compass needle would
move?
The north pole of the compass needle would move towards east
direction.

17. 11)What will happen if
i) The polarity of the battery is changed, will tehre be any change in the direction
of reflection of the needle. If so, what is the direction of reflection.
ii) If the circuit is not close or key (K) is removed will there be deflection in the
magnetic compass.
iii) Show the direction of current in the copper wire if the polarity is reversed.
Ans=>
i) Yes there will be change in the direction of the deflection of the needle, the
direction will be towards west direction.
ii) No if the circuit is not closed or key is removed there will be no deflection in
magnetic compass.

18. Magnetic field due to straight current carrying
conductor:

19. 1. The magnetic field lines around a straight conductor carrying
currents are concentric circles whose center lines on the wire.
2. The direction of magnetic fields around the conductor carrying
current can be found by using right hand thumb rule.
3. The magnetic lines can be drawn with the help of a magnetic
compass.
4. Magnetic field∝current
5. Magnetic field∝
1
𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒

20. RIGHT HAND THUMB RULE

21. • A current carrying conductor is imagined to be held in the right hand
such that thumb points towards the direction of current.
• Then the direction in which the fingers encircle the wire will give you
the direction of the magnetic field .
• Magnetic field α current
• Magnetic field α
1
𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒

22. 12) The current flows in a straight conductor from north-south in which
direction a north pole of magnetic compass is expected to move?
Towards east direction
13) What could happen to the direction of deflection of the compass
needle if the polarity of the battery is reversed?
The deflection of the compass needle be towards west.

23. 14) What could happen to the deflection of the compass needle placed at a
given point of
(i) The strength of current is increases.
(ii) Magnetic compass is taken away from current carrying conductor.
Ans=>
(i) Magnetic field∝ 𝑐𝑢𝑟𝑟𝑒𝑛𝑡
Magnetic field ∝
1
𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒
When the strength of current increases, magnetic field also increases.
Hence the deflection will be more.
(ii) When the distance from current carrying conductor increases, the
magnetic field decreases.

24. MAGNETIC FIELD DUE TO A CIRCULAR COIL
CARRYING CURRENT

26. 1. At every point of a current carrying circular coil (or) loop there are concentric
circles representing the magnetic field around it.
2. As we move away from the wire the circles become larger and larger.
3. At the center of the circular coil the arcs of the circle appears as straight lines
pointing in the same direction. Therefore, the magnetic field is strong at the center
of the loop.
4. The direction of magnetic field can be found by applying right hand thumb rule.
5. The magnetic field at the center
Magnetic field ∝ current(I)
Magnetic field ∝ number of turns(n)
Magnetic field ∝
1
𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒
.

27. UNIFORM MAGNETIC FIELD:
• If the magnetic field is the same at all points then the magnetic field
is said to be uniform.
Eg:
Magnetic field inside a solenoid.

28. NORTH AND SOUTH POLE IN A CIRCUALAR
COIL CARRYING CURRENT:

29. MAGNETIC FIELD DUE TO A CURRENT
CARRYING SOLENOID

30. A coil of many circular turns of insulated copper wire wound on a
hollow cylinder of insulated material is called a solenoid
1.When current is passed through the solenoid magnetic field is
produced .
2.The magnetic field of a solenoid is similar to that of a bar magnet.
3.As we move away from the wire the circles become larger and larger.

31. 4. Magnetic field at the centre is strong.
5.Magnetic field due to circular coil
Magnetic field α current (I)
α number of turns (n)
α
1
𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒
What is meant by uniform magnetic field?
If the magnetic field is the same at all points then the magnetic field is said to be
uniform.
Eg:
i) Magnetic field inside a bar magnet.
ii) Magnetic field inside a solenoid.

32. • What happens to the magnetic field produced in a solenoid when the
current is put off ?
The magnetic field will be lost.
• What is an electromagnet ?
The magnetic field produced inside a solenoid can be used to
magnetise a piece of magnetic material like soft iron when placed
inside the coil.
The magnet so formed is an electromagnet .

33. • A current carrying solenoid is suspended freely. What happens to the
solenoid?
It will align along north south direction.
• What is the magnetic field due to a current carrying long straight solenoid?
i) Outside the solenoid
ii) Inside the solenoid
Outside the solenoid:
It is very weak and it is almost zero.
Inside the solenoid:
A magnetic field is uniform and strong.

34. • Write short note on permanant magnets?
1. Permanent magnets are made of carbon steel, chromium steel,
tungsten steel and some alloys like Alnico and Nipermag .
2. If the rod which is magnetised using solenoid is made of steel, the
magnetism acquired will not be lost even after the removal of
current. Such magnets are called permanent magnet.

35. • NOTE
1. Alnico is an alloy of Aluminium, Nickel and Cobalt .
2.Nipermag is an alloy of Iron, Nickel ,Aluminium and Titanium

36. DIFFERENCE BETWEEN TEMPORARY MAGNET
AND PERMANENT MAGNET
TEMPORARY MAGNET
1.Magnetism acquired will be
lost after the removal of current
2.Magnetic poles can be changed by
reversing the direction of current.
3.Strength of the magnet can be
changed by increasing the current.
4.Very strong
5.Can be easily demagnetized.
PERMANENT MAGNET
1. Magnetism acquired will not be
lost .
2.Magnetic poles cannot be changed
.
3.Strength of the magnet cannot be
changed .
4.Not very strong like temporary
Magnet.
5.Cannot be easily demagnetized.

37. • Why the magnetic field is strong inside the solenoid ?
The magnetic field due to each turn of the solenoid gets added up so
the magnetic field is uniform and strong .

39. FORCE ON A LINEAR CURRENT CARRYING
CONDUCTOR

40. • When a current carrying conductor is placed in a magnetic field it
experiences a force.
• The direction of force experienced by the current carrying conductor
is found by using FLEMING’S LEFT HAND RULE.

41. • AB is the current carrying aluminium rod suspended horizontally
between the pole pieces a horse shoe magnet with the magnetic field
directed upwards.The circuit is arranged in such a way that the
current and the magnetic field are perpendicular to each other.
1.When current passes through the rod from B TO A the rod gets
displaced towards left.(west)
2. If the direction of current is revesed the displacement of the rod
also gets reversed.
3.The direction of the displacement of the rod also gets reversed if the
poles of the magnet is inter changed .

42. • The force on the current carrying conductor is perpendicular to the direction of current and the magnetic
field.
On what factors the direction of force on a current carrying conductor depends.
The direction of force on the current carrying conductor depends on
1) The direction of current
2) The direction of the magnetic field
3) The angle between the magnetic field and the current
When is the force on the current carrying conductor in the magnetic field is maximum.
F =BI Lsinθ
Θ =900
Sin90o=1
Then F = BI L
The current carrying conductor experiences maximum force, when the angle between the magnetic field and
the current is 900.

43. • When is the force on the current carrying conductor minimum.
F =Bi l sinθ
• When the angle between the magnetic field and the current is 00
Then sinθ=0
F =BI l x 0
F =0

44. • A current carrying solenoid is suspended freely what happens to the
solenoid.
It will align along north south direction.
• What is the ,magnetic field of a long straight solenoid.
I. Outside the solenoid.
II. Inside the solenoid.
III. Outside the solenoid: it is very weak almost zero.
IV. Inside the solenoid: the magnetic field is uniform and strong.

45. • A current carrying solenoid is used to magnetise a steal rod shown by
means of a diagram also indicate the poles induced in the steel rod.

46. • Mention some basic properties of a magnet.
1)Magnets attracts small pieces of iron,nickel,cobalt etc.
2) A freely suspended magnet comes to rest along north and south direction.
3) Like poles repel unlike poles attract.
4) Magnetic poles always exist in pairs.
• Mention the uses of
1. electromagnet –Electric bell ,loud speaker,electric motor
telephone,electric fan,crane
2. permanent magnet –microphone, electric clock,ammeter
,voltmeter,speedometer

47. • What type of magnetic field is produced due to a current carrying
a)straight conductor
b)straight solenoid
ANS=>
a) concentric loop in a plane perpendicular to the straight conductor with
the straight conductor as centre.
b)closed loops similar to that of a bar magnet.
• What happens if a bar magnet is cut into pieces?
1.transverse to its length
2. along its length
• In both cases we get two magnets each having north and south pole.

48. • When a bar magnetis cut transverse to its length
again we get two magnets.The pole strength of each part is same as
that of original magnet .But its magnetic moment is halved because its
length is halved.
• When a bar magnet is cut along its length
the pole strength of each part is halved so its magnetic moment is
also halved.
• NOTE : Magnetic moment = pole strength x length of the magnet .

49. • Mention some devices that use current carrying conductor and
magnetic field .
Electric motor, measuring devices like ammeter ,voltmeter and
galvanometer
• ELECTRIC MOTOR
• An electric motor is a device which converts electric energy into
mechanical energy.

50. • PRINCIPLE
1.When a current carrying coil is placed in a magnetic field it
experiences a force
2.The direction of force experienced by the current carrying conductor
is found using FLEMING’S LEFT HAND RULE.

51. ELECTRIC MOTOR

52. • CONSTRUCTION
It consists of a rectangular coil ABCD of insulated copper wire called
armature (wound over a rectangular iron core )
2.The coil is placed in a strong magnetic field.
3.The two ends of the armature coil are connected to split ring
commutator R 1 and R 2.
4.Two carbon brushes B 1 and B 2 are made to press lightly against the
split rings R 1 and R2.
5.The purpose of the split ring commutator is to reverse the direction
of current through the coil after every half rotation.

53. • The armature coil is free to rotate about an axis which is perpendicular to the
magnetic field. The battery connected across the carbon brushes supplies electric
current to the armature coil
• WORKING
1.Suppose the coil lies in the horizontal position when the current is switched on.
2. The direction of current through the armature coil along ABCD. The direction of
force action on the coil is given by Fleming’s left hand rule.
3. The arm AB of the coil experiences a downward force and the arm CD
experiences an upward force. The equal and opposite forces make the coil to rotate
in the anticlockwise direction.
4 When the coil reaches the vertical position the force on the coil becomes zero
and R2 looses contact with B! and B2.

54. But due to inertia of motion, the coil rotates further. The split rings R1 and
R2 change contact from one brush to the other (B1 to B2).
5. The change of contact reverses the direction of current through the coil .
The current flows along DCBA in the coil.
6. The side AB is now on the right side with upward force and the side CD is
on the left side with downward force coil again rotates in anticlockwise
direction.
7. Each time in its rotation the coil passes the zero force position. The
current through the coil reverses after half rotation.
8. The coil rotates continuously in the same direction (ie) anticlockwise
direction as long as the current passes through the coil.

55. • Uses of Electric Motor.
Used in domestic appliances such as electric fan mixie grinder.
Used in lift and locomotive.
In cars wind screen wiper is driven by electric motor. Engine is started by another
motor.
• Fleming’s Left hand rule:
Stretch the fore finger , the central finger and the thumbof the left hand so that
they are mutually perpendicular to each other.
If the fore finger points the direction of the magnetic field.
The central finger the direction of current.
Then the thumb points the direction of motion /force experienced by the current
carrying conductor.

56. ELECTROMAGNETIC INDUCTION
• DEFINITION
1. It is the phenomenon according to which a potential difference and hence
a current is induced in a closed coil whenever the magnetic field lines linked
with he coil changes.
The current induced is called induced current .
The voltage induced is called induced voltage or induced
e.m.f.(electromotive force )
2. It is the phenomenon due to which whenever a conductor moves inside a
magnetic field or a magnetic field is changing around a fixed conductor an
emf is induced in the conductor and hence a current is induced in the
conductor.

57. FARADAY”S EXPERIMENT

60. 1. When the magnet is moved towards the coil of wire, there is a
momentary deflection in the needle of the galvanometer say towards right.
This indicates the flow of current in the coil.
2.When the motion of the magnet stops the deflection becomes zero in the
galvanometer. There is no flow of current in the coil.
3. When the magnet is moved away from the coil the galvanometer deflects
towards left. This indicates the flow of current in the coil. The direction of
current is opposite to that when the magnet was moving towards the coil ,
therefore when ever the magnetic field lines linked with the coil changes.
there is induced voltage and hence induced current in the coil connected to
the galvanometer.

61. • Mention two ways by which the direction of current in the coil can be
changed in the above experiment?
1. When the north pole of the magnet is moved towards the coil, the
deflection of the needle in the galvanometer is to the right.
2.When the northpole of the magnet is moved away from the coil the
deflection in the galvanometer will be opposite.(left)
(or)When the south pole of the magnet is moved towards the coil then
also the deflection will be to the (left).

62. • GALVANOMETER:
• It is a device used so detect the presence of current in the circuit.
• The pointer in the galvanometer remains at zero when no current
flows through it.
• Depending on the direction of current the pointer deflects towards
left or right of the zero in the galvanometer.

63. FARADAYS EXPERIMENT 2.
EXPERIMENT

64. • When the current in the primary coil c1 changes, the magnetic field of
c1 changes thus the magnetic field lines associated with the secondary
coil c2 also changes.
• The change in magnetic field lines associated with the primary coil c1
Causes induced voltage in c2.Hence, induced current is produced in c2.
• whenever, the current in c1 changes a potential difference is induced
in c2 and hence induced current flows in c2.
• During the make and break of the circuit there is induced voltage in
c2.

65. • Mention two ways by which induced current can be produced in a coil?
1. By moving the coil in the magnetic field.(A.C generator)
2. By changing the magnetic field around the coil.
(Faradays' experiment).
• A current carrying coil in a magnetic field when the force experienced by the coil will be is
maximum?
When the direction of motion of the coil is at right angle to the magnetic field
Or
the angle between the magnetic field and the direction of current must be 900.
F=B l L sin𝜃
when 𝜃= 900
F=B I L (maximum)
Where 𝜃 is the angle between I and B

66. • State the rule used to find the direction of induced current?
Flemings right hand rule
Stretch the forefinger, thumb and the central finger of the right
hand so that they are mutually perpendicular to each other.
• If the forefinger points the direction of magnetic field.
• Thumb shows the direction of motion of the conductor.
• Then, the central finger gives the direction of induced current.