Section-A

EXPERIMENT 1

AIM
ineresistivity of twolthree wires by plotling a graph for potential difference versuscurrent.
APPARATUS
A woeietancewire (of different
such as copper, iron, constantan, etc), a
material
ammeter (0-3)A
appropriate range, a battery (battery
of
voltmeter (0-3) and an V
eliminator),a rheostat, a metre scale, one way
wires and a piece of sand paper. key, connecting

THEORY
According to the Ohm's law "the
current flowing through a
a:oronce across its ends, provided conductor is directly proportional
the physical conditions (temperature, to the potential
omains the same.IfI be the current flowing dimensions, pressure, etc.) of the
conductor
through a conductor and be the V
potential difference across its ends,
then according to Ohm's Law,

V«I or V= RI
where. R is the constant of
proportionality. It is known asresistance of the conductor.

We know, R=p,
where r isresistivity or sp. resistance.

L 4pL TDR
= p p= 4L
TD2
4
R depends upon the nature of material,
temperatureand dimensions of the conductor.
In SI units, the potential
difference V is measured in volt and the current I in ampere,the resistance
measured in ohm. R is
(1) Toestablish the current-voltage
relationship, it is to be shown that the ratio VI remains
given resistance. Therefore, a graph between the constant for a
potential difference (V) and the current ()must be a straight line.
(2) The constant ratio gives unknown
value of resistance,
-a)
CIRCUITDIAGRAM

Battery

Rheostat

A
Unknown resistance
wire

Fig.Cireuit diagram.

13
14
COMPREHENSIVE PHYSICS ACTIVITIES
VOL.
-XI|
PROCEDURE
1. Arrange the apparatus in the same manner as
given in the arrangementdiagram.
2. Clean the ends of the connecting wires with sand paper to remove the
insulations, if any.
8. Make neat, clean and tight connections according to thecircuit diagram.While
making connections en
sure that +ve marked terminals of voltmeter and
ammeter are joined towards the +ve terminal of the
battery.
4. Determine the least count of voltmeter and ammeter,and also note the
zero error, if any.
6. lnsert the key K,slide the rheostat
contact and see that ammeter and voltmeter
6. Adjust the sliding contact of the areworking properly.
rheostat such that a measurable
coil or the current passes through the resistance
resistance wire.
7.Note down the value of potential
difference V from voltmeter and
8. Shift the rheostat contact current I from ammeter.
not in fractions. slightly so that both ammeter and voltmeter
show full divisions readings and
9.Record the readings of the voltmeter
and ammeter.
Note.In case of battery
eliminator, follow these steps:
Turn the knob at2V in battery
record the reading and put the
eliminator contact point in rheostat at
in voltmeter fixed position. Now,
and ammeter.
Withoutdisturbing the rheostat,
turn the knob of battery
and record
volts to different voltages,
say 4, 6, 8, 10 and 12
corresponding readings in voltmeter and
10. ammeter.
Take atleast five sets of
independent observations.
11. Cut the resistance
wire at the points where
metre scale. it leaves the
terminals, stretch it and find its length by the
12. Record your
observations.
13. Next repeat
abovesteps by taking other
wires.

Rheostat
One-way
key

Cell (or Battery eliminator)

Resistance wire

luly
A

Ammeter

Voltmeter
Fig. Arrangement
diagram.
 15

EXPERIMENTS

OBSERVATIONS 4. Zero error

1. Length
Length of the resistance wire l=,...... Zero error in ammeter,e,= ......

Zero error in voltmeter, e, =......

2. Range
Rangeof the given ammeter = ..... 5. Zero correction
given voltmeter = Zero correction for ammeter,c,=-e,=.
Rangeof the
Zero correction for voltmeter, C =-e, =.
3. Least count
Least count of ammeter
=
voltmeter =......
Least count of

Table for Ammeter and Voltmeter Readings

6.

Wire 1
V() =R
Ammeter ReadingI(A) Voltmeter Reading
Serial No. of

Observed Corrected (Ohm)

Obs.
Observed Corrected

I=I,tej V=V,tcg
(36) (4)
(2a) (26) (3a)
(1)

1.

resistance, R=.... ohms.

Mean value of

CALCULATIONS Graph between Potential Difference and Current

Vand I for each set of observations.
1. Find the ratio of Scale :
difference V (column
3b)
: 1 cm =0.5 V of potential difference
Plot agraph between potential X-axis
=
2.
taking Valong X-axis
and I Y-axis :1 cm 0.25 mA of current
and current I (column 26), line
Y-axis. The graph
comes to be a straight
along
(passing through the origin).
from the following
The resistance can be
calculated

graph:
AB AI ...(1)
In AABC, tan
CB AV
amperes
in
AV
Or Cot = ...2)

0.5

AV
CurrentH
...3)
But, R= AI
R= cot
...(4)

1.0 2,0
30
R=..... Q. O0
(V) in volts
Potential difference

ofthe wire.
Constantratio resistance potentialdifference
I gives
8.
Fig. Graph between
cm-, S2 and current. It is a straight line.
4. Resistance of the wire per cm=....
16
COMPREHENSIVE PHYSICS ACTIVITIES
VOL.
XII
5, Finding the dianmeter of wire 1.

Table for diameter (D)of the wire 1

Serial No.Linear Scale Circular Scale Reading Observed diameter Corrected

of Obs. N
Reading
(mm)
No. of
scale
cireular Value D,=N+nx L.C. diameter
division n x (L.C.) (mm) D= D, +c
on (mm)
reference
(mm)
line(n)
(1)
(2)
(3a) (36) (4) (5)
1
(a)
(b)
D, (a) = D, (a) =
2.
(a) D, (6) = D, (6) =..
(6) D, (a) = D, (a) =.....
(a D, (b)= D, (6) =
D,(a) = D, (a) =
Mean D = D, (6)= D, (b)=
Area (A) =TD
4 -.... m²
6.Finding the lengths of the
wire 1.
Mean length, +Ly t Lg
whereL,Lg Lg are
L= m lengths of wire 1.

Table for
unknown resistance (X)
Serial No. of
Resistance from the
Obs. Length AB =l
resistance box Length
(cm)
BC =(100 -) Unknown
X=R
resistance
00-)
(1) (ohm)
(cm)
(2)
1. (3
(ohm)

2
(4)
(6)
3.

RESULT
X, = .....

(i)
Resistivity of the
(ii) The graph wire is
betweenV and I is
..... 2m.
Note.By astraight line,
noting the passing
resistivity (or
specific
throughthe
PRECAUTIONS resistance)from
origin,.

1.The thetable,
connections should percentage error
2. Thick beneat,clean can be
wires and tight. calculated.
with sand shouldbeused for the
paper. connections after
3.Voltmeter
and removing the
4. A low ammeter should
be of proper insulations near their
5.The resistance ends by
key should berheostat should be used. range. rubbin
inserted only
resistance will while taking
increase).
observations to
SOURCES OF ERROR avoid
heating of
resistance
1. The (otherwiseite
instrumentscrews may
2.Thick be loose.
connecting wires may
3.Rheostat not be available,
may have high
resistance.
 EXPERIMENT 2

AIM
Bedresistance ofagiven wirelstandard resistor using netre bridlge.

APPARATUS
Ametre bridge (slide wire bridge), a Leclanche cell (orBattery eliminator), a galvanometer, a resistance box,
a one-way key, a resistance wire, square connecting wires and a piece of sand paper.
jockey,
a
THEORY
The unknown resistance X is given by

X= (100 – ) xR

where R is in the left gapandunknown resistance

known resistance placed X in the right gap of metre bridge. l cm

is the length of netre bridge wire from zero end upto balance point.

CIRCUIT DIAGRAM
Known resistance Unknown resistance

R
RB
Resistance
I
box

Galvanometer

10 20 30 40 50 60 70 80 90 100
luu,
uuauuluaunuunualnumluu

A
(100 – )
K

(Battery eliminator)
Leclanche cell
diagram--Metre bridge.
Fig. Circuit

PROCEDURE
For Resistance
diagram.
Arrange the apparatus as shown
in the
C and B. Take
1,
in the right gapbetween
resistance wire whose resistance is to be determined
2. Connect the
wire forms a loop.
care that no part of the B.
hand gap between A and
box of low range in the left
3. Connect resistance
as shown in the circuit diagram.
4. Make all the
other connections
the key K.
2 ohm) from the resistance box, plug
(say
5. Take out some resistance wire.
at right end of the bridge
atleft end and then
Touch the jockey gently first
6.

17
 COMPREHENSIVE PHYSICS
ACTIVITIES
7. Note the deflectionsinthe VOL.
-XIL
galvanometer,Ifthe galvanometer shows
the connections are correct. deflections in opposite
If the deflection is one side only, then there is
Check or take help of your some fault directions,
teacher and rectify the fault. the circuit.
8. Move (slide) the jockey
gently along the wire from left
The to right till galvanometer
point where the jockey is touching gives Zero
9.
the wire is null point D.
Choose an deflection.
appropriate value
fromthe resistance box
of R
nometerwhen the jockey is suchthat there is no deflection
nearly in the middle in
of the wire (i.e., the galva-
10. Note the between 45 cm to 55 cm).
11. Take at
position of point D
(with the help of
a set-square) to know
12. Record
least four sets of
observations in the
same way by changing
balancing length,AD 1. =
your observations. the value of in R steps.

One-waykey

)
Leclanche cell

Resistancebox

=? Unknown
wire

10 20 30
(100-I) 40
70 80 50 60
A 90 100
Auuululuuhunhuluuluulunlualuluuluuluuuuuuubuu
Scale

Bridge wire

Galvanometer
Fig.
Arrangement diagram.
OBSERVATIONS
1. Length
of
given
wire,L=.... cm.
2.
Table for
Serial No. of unknown resistance (X)
Resistance from
Obs. the
resistance boxc
Length AB=l
Length
BC =(100-) Unknownresistance
(cm)

(ohm)
R
X=R (100 -)
(1)
(cm)
(2)
(3) (ohm)
(4)
2.
(5)
3.
X
4.
X, =
......
VITIES VOL. I-X
EXPERIMENT'S
osite
directions.
t in the circuit. CALCULATIONS for X
1. Calculation

zero deflection. )
ie) From position of D, find cm and write in column
-
l

6) Find length (100 cm and write in column 4.

e) Calculate X and write in column
of Table 1.

5.
on in
m).
the galva
Mean X A1t X2 +
4
X +X, ohm
D =l. Shondard value of the resistance of the given wire (from resistance bx),
teps. X, = ...... ohm-m
X- X
x 100
Percentage error

=...... %.

RESULT
1. The value of unknown resistance, X= ...... 2
2.Percentage error =
PRECAUTIONS
1. The connections shouldbe neat, clean and tight.
2. the plugs in the resistance box should be tight.
All
wire and do notrub it.
3. Move the jockey gently over the bridge
when the observations are to be taken.
4. The plug in key K should
be inserted only

5. should be brought between 45 cm and 55 cm.

Null point
error of parallax.
6. Set square shouldbe used to note null point to avoid
7. The wire shouldnot make a loop.

SOURCES OF ERROR
1. The instrument screws may be loose.
The plugs may not be clean.
2.
thickness.
3. The wire may not have uniform
like back lash error and wrong pitch.
4. The screw gauge may
have faults

ce