Activity -4
To
study the field lines formed around a bar magnet
Objective
To study field lines
formed around the bar magnet.
Theory
- Magnets
have two types of poles: north poles and south poles.
- The
magnetic strength at the pole is the strongest.
- When
a bar magnet is suspended freely in a horizontal position, the bar magnet
will align itself in north-south direction, where the north pole of the
magnet points to the north pole of the Earth.
- Like
poles repel and unlike poles attract.
- Magnetic
materials such as iron, nickel, steel etc. are attracted by the magnets.
- Attractive
and repulsive force of magnet depends how strong the magnet is.
- Magnetic
force also depends on distance between the magnet and the object.
Materials :
White paper
sheet, drawing board, adhesive, bar magnet, iron filings and magnetic compass.
Procedure :
1.
Fix a sheet of white paper on
a drawing board using some adhesive material.
2.
Place a bar magnet in the
center of it.
3.
Sprinkle some iron filings
uniformly around the bar magnet.
4.
Now tap the board gently.
5.
Observe the pattern in which
the iron filings arrange themselves.
Observation
1.
The strength of the
magnetic field is inversely proportional to the distance between the field lines.
2.
Magnetic field lines
never cross each other. It is unique at every point in space.
3.
Magnetic field lines
begin at the north pole of a magnet and terminate on the south pole.
Activity -5
Magnetic field lines around current
carrying conductor
Objective:
To observe the magnetic
field lines around current carrying conductor.
Theory:
- Magnetic
effect of electric current is
one of the major effects of electric current in use, without the
applications of which we cannot have motors in the existing world.
- A
current carrying conductor creates a magnetic field around it, which can
be comprehended by using magnetic lines of force or magnetic field lines.
- The
nature of the magnetic field lines around a straight current carrying
conductor is concentric circles with centre at the axis of the conductor.
- The
strength of the magnetic field created depends on the current through the
conductor.
- The
direction of the magnetic field lines of force around a conductor is given
by the Maxwell’s right hand grip rule or the right
handed corkscrew rule. Imagine that you are holding a
current-carrying straight conductor in your right hand such that the thumb
points towards the direction of current. Then your fingers will wrap
around the conductor in the direction of the field lines of the magnetic
field. This is known as right hand thumb rule.
Apparatus:
A battery (12 V), a variable resistance (or a rheostat),
an ammeter (0–5 A), a plug key, and a long straight thick
copper wire.
Procedure:
- Fix the cardboard
and insert the wire through the centre of cardboard such that it is normal
to its plane.
- Connect the wire
with rheostat, ammeter, battery and plug key in series.
- Sprinkle the iron
filings uniformly on the cardboard.
- Keep the
variable of the rheostat at a fixed position and note the current
through the ammeter.
- Close the key and
gently tap the cardboard.
- Observe the
pattern of the iron filings over the cardboard.
Observations
1.
You will observe that
the magnetic field lines are formed in concentric circles around the current
carrying conductor. These lines do not intersect each other and are equidistant from
each other.
2.
The direction of
the field is perpendicular to the conductor.
3.
The magnetic
field (B) acting on the object O increases as the
current flowing through it increases.
4.
The field increases as object
O is closer to the conductor and decreases as
it moves away from the conductor.
5.
The direction of
magnetic field lines gets reversed if the direction of current is
reversed.
Activity -6
Force on a current
carrying conductor in a magnetic field
Objective:
To study
the force on a current-carrying straight conductor in a magnetic field and to
verify that the motion of the conductor is according to Fleming’s left-hand
rule.
Theory:
A current carrying conductor
placed in a magnetic field experiences a force. If the direction of the field
and that of current are mutually perpendicular to each other, then the force
acting on the conductor will be perpendicular to both and that can be
determined using the Fleming’s left-hand rule. When current establishes in the
conductor, it gets displaced which verifies the existence of a force on the
conductor.
Fig. - A current-carrying
rod, AB, experiences a force perpendicular to its length and the magnetic field
Fig. - Fleming’s left hand rule.
Apparatus:
A horse
shoe magnet, a small aluminium rod, an ammeter, two wooden
stands, two connecting wires, a battery, a plug key.
Procedure:
- Suspend the
aluminium rod horizontally from the stand using clean connecting wires.
- Place the
horse-shoe magnet in such a way that the rod lies in between both the
poles such that south pole is vertically above and north pole is
vertically below the rod.
- Connect the rod in
series to the battery, key and the rheostat.
- Now switch on the
current and observe the displacement of the rod.
- Reverse the
direction of the current and observe the change in the displacement of the
rod.
Observation:
On passing
current through a straight conductor (aluminium rod) kept in a magnetic field,
the conductor gets displaced upward or downward.
Inference:
- The direction of
displacement of the conductor rod changes with the change in the direction
of current through it.
- The displacement
of aluminium rod is in accordance with Fleming’s left-hand rule.
Activity -7
Electromagnetic Induction
Objective:
To study
the phenomenon of electromagnetic induction.
Theory:
The phenomenon of electromagnetic induction is the existence of an
induced current in a circuit (such as a coil) placed in a region where the
magnetic field motion changes with the time. The magnetic field may change due
to relative motion between coil and magnet placed near the coil as shown in the
Fig. 1. We know that a current-carrying conductor also produces magnetic field
that changes with a change in the current flowing through it. Thus if a coil is
placed near to a current-carring conductor, an induced current in the coil may
setup due to a change in the current through the current-carrying
conductor.
Fig.:
Moving a magnet towards a coil sets up a current in the coil circuit,
as
indicated by deflection in the galvanometer needle.
Apparatus:
Magnetic
bar, a galvanometer, coil and connecting wires.
Procedure:
- Take a coil of
wire having a large number of turns.
- Connect the end of
the coil to a galvanometer.
- Take a strong bar
magnet and move its north pole into the coil and observe the changes in
the galvanometer needle.
- Repeat earlier
step with the south pole of the bar magnet.
- Now repeat the
procedure with the coil having a different number of turns and the variation
in the deflection of the galvanometer needle.
Observations:
- When we move the
magnet in or out of the coil, the needle of galvanometer gets deflected in
different directions.
- When we insert the
north pole (N) of bar magnet into the coil, the needle gets deflected in
negative direction.
- When we insert the
south pole (S) of bar magnet into the coil, the needle gets deflected in
positive direction.
- When we move the
bar magnet in or out of the coil with varying speed, the speed of
deflection changes accordingly.
- As we increase the
number of turns in the coil, the deflection increases.
Inference:
- The deflection of
galvanometer needle indicates the presence of current in the coil.
- The direction of
deflection gives the direction of flow of current.
- The speed of
deflection gives the rate at which the current is induced.
- The deflection in
galvanometer changes with the change in number of turns in the coil - more
the number of turns in the coil greater is the deflection.
Activity -8
To find focal length of a
Concave Mirror
Objective -
To determine the focal
length of a concave mirror, by obtaining image of a distant object.
Theory
- A
concave mirror, like a plane mirror, obeys the laws of reflection of
light.
- Rays
of light from object - The rays of light coming from a distant object e.g.
sun or a distant building can be considered to be parallel to each other.
When these parallel rays of light fall on a concave mirror along its axis,
reflect and meet at a point in front of the mirror, which is called
as Principal focus of the mirror.
- A real, inverted and very
small image size is formed at the focus of the mirror.
- Focal
Length - The distance between the pole P of the concave
mirror and the focus F is the focal length of the concave
mirror. Thus, the focal length of a concave mirror can be estimated by
obtaining a 'Real image' of a distant object at its
focus, as shown in the figure.
Material Required -
A concave mirror, a
mirror holder, a white screen fixed on a stand or a white wall, an
object (candle) and a metre scale.
Procedure -
1.
Fix concave mirror to
mirror holder and place it on table.Turn the face of mirror towards a distant
object (a candle in this case). The selected object should be visible with your
naked eyes.
2.
Adjust the position of
the screen in such a way that it forms a clear image of the candle on the
screen.
3.
Measure the distance
between the concave mirror and the screen with a metre scale. Record your
observations in observation table.
4.
Repeat the experiment
two or three times and find the mean value of the focal length.
NOTE: STUDENTS WE WILL DRAW THE TABLE IN SCHOOL WHILE
PERFRMING THE EXPERIMNT AND WRITE RESULT SIMULTANEOUSLY.
Activity -9
To study reflection in
concave mirror
Objective:
To study reflection in
concave mirror and observe image formations for different positions of the
object.
THEORY
- Reflection:
Whenever light, travelling in one medium, comes in contact with surface of another medium, a part of it is returned into the first medium. The phenomenon of returning of light into first medium is known as reflection of light. - Concave
mirror:
A concave mirror is that spherical mirror in which the reflection of light takes place at the concave surface i.e. bent-in surface. - Pole:
It is the center of the reflecting surface of the concave mirror also called vertex of mirror, generally denoted by letter ‘P’.
- Center
of curvature:
It is the center of that sphere of which the concave mirror forms a part, denoted by letter ‘C’. - Principal
axis:
The straight line passing through the center of curvature and pole of concave mirror is called its principal axis. - Principal
focus:
A beam of light incident parallel to the principal axis, after reflection from the spherical mirror, either actually converges to or appears to diverge from a fixed point on the principal axis. The fixed point is called the ‘Principal focus’, denoted by letter 'F'. - Laws
of Reflection:
1) The angle of incidence is equal to the angle of reflection.
2) The incident ray, the reflected ray and the normal at the point of incidence, all lie in the same plane. - Types
of images:
1) Real image: If the reflected rays actually meet at a point, then the image formed is real. It can be obtained on screen.
2) Virtual Image: If the reflected rays do not actually meet at a point but appear to diverge from a point, then the image formed is virtual.
Images of an object, formed by a concave mirror, when the
object is placed at various positions:
When object is at
infinity.
|
When object is beyond
centre of curvature('C').
|
When object is at
centre of curvature ('C').
|
When object is between
'C' and 'F'.
|
When object is at
focus 'F'.
|
When object is between
'P' and 'F'.
|
Materials required:
A concave mirror, a
mirror holder, a semi transparent screen fixed to a stand and a small candle
with stand.
Procedure
- Fix
the concave mirror in the mirror holder and place it on edge of the table.
- Mount
a small candle vertically on a stand. Place it in front of the concave
mirror on the left hand side (i.e. shiny surface) say on focus 'F'.
- Place
the screen such that the lower level of screen must be so arranged that it
remains just above the principal axis of the mirror.
- Locate
a sharp image of candle by adjusting the position of the screen. Note and
record the position and nature of the image formed on the screen.
- Repeat
the experiment by placing candle at different positions .
Activity -10
To study refraction of
light in rectangular glass slab
OBJECTIVE:
To trace the course of different rays of light through a rectangular glass slab
at different angles of incidence, measure the angle of incidence, refraction
and verify Snell`s law. Also measure the lateral displacement.
Apparatus:
A drawing board, rectangular glass slab, office pins, sheet of
white paper, a protractor and sharply pointed pencil.
Procedure:
- Fix a sheet of
white paper on a drawing board with drawing pins. Place the given glass
slab nearly in the middle of the sheet.
- Mark the boundary
of the glass slab with a sharp pencil and label it as PQRS after removing
the slab from its position.
- On the line PQ
mark a point E and draw a normal N1EN2 at it. Draw a line AE making angle
AEN1 with the normal.The angle should neither too small nor too large (say
about 40 degree).
- Now place the
glass slab again on its boundary PQRS and fix two pins A and B vertically
about 10 cm apart on the line AE (say points A and B).
- Look through the
glass slab along the plane of the paper from the side SR and move your
head until the images of the two pins A and B are seen clearly. Closing
your one eye ,adjust the position of your head in such a way that the
images of the pins A and B lie in the same straight line.
- Fix two other pins
C and D vertically in such a way that the images of the pins A and B and
pins C and D, all these four, lie in the same straight line. Ensure that
the feet of the pins ( not their heads ) lie in the same straight line.
- Remove the slab
and also the pins from the board and encircle the pin-pricks on the
paper,with a sharp pencil.
- Join the points D
and C and produce the line DC towards the slab so that it meets the
boundary line RS at the point F. Join the points e and F. Thus for the
incident ray represented by line AE, the refracted ray and the emergant
ray are represented by EF and FD respectively.
- On the line RS
draw a normal N1'FN2' at point F. Now, with a protractor, measure
angle AEN1, angle FEN2 and angle DFN2' labelled as angle i, angle r and
angle e respectively.
- Now place the
glass slab at some other position on the sheet of paper fixed on the board
and repeat all the above steps again taking another angle of incidence.
- Measure the angle
of incidence i.e angle of refraction, angle of emergence, again.
- Make a record of
your observations in the observation table as shown below.
Observation Table :
status 2020
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