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[CLASS XII- PHYSICS - PRACTICAL] 2022-
Note :
The record to be submitted by the students at the time of their annual examination has to include:
1. Record of at least 8 Experiments [With 4 from each section], to be performed by the students.
2. Record of at least 8 Activities [With 3 each from section A and section B], to be performed by the
students.
3. The Report of the project carried out by the students.
EXPERIMENT – 1
Aim: To determine resistance per cm of a given wire by plotting a graph of potential difference versus current. Apparatus: A metallic conductor (coil or a resistance wire), a battery, one way key, a voltmeter and an ammeter of appropriate range, connecting wires and a piece of sand paper, a scale.
Formulae Used: The resistance (R) of the given wire (resistance coil) is obtained by Ohm’s Law R
I
V
Where, V : Potential difference between the ends of the given resistance coil. (Conductor) I: Current flowing through it.
If l is the length of resistance wire, then resistance per cm of the wire =
l
R
Observation: (i) Range: Range of given voltmeter = 3 v Range of given ammeter = 500 mA
(ii) Least count: Least count of voltmeter = 0.05v Least count of ammeter = 10 mA (iii) Zero error: Zero error in ammeter, e 1 = 0
Zero error in voltmeter, e 2 = 0
Ammeter and Voltmeter Readings:
Sr. No.
Ammeter Reading I (A) Voltmeter Reading, V (v)
R
I
V
Observed Value Observed Value
1 50 500 mA 16 16x0.05=0.8 1.6
2 35 350 mA 11 0.55 1.57
3 32 320 mA 10 0.50 1.56
4 19 190 mA 6 0.30 1.58
5 10 100 mA 3 0.15 1.5
Mean R = 1.
Length of resistance wire: 28 cm
Graph between potential difference & current:
Scale: X – axis : 1 cm = 0.1 V of potential difference Y – axis: 1 cm = 0.1 A of current
The graph comes out to be a straight line.
Result: It is found that the ratio V/I is constant, hence current voltage relationship is established i.e. V I or Ohm’s
Law is verified.
Unknown resistance per cm of given wire = 5.57 x 10-2^ cm-
Precautions: Voltmeter and ammeter should be of proper range.
The connections should be neat, clean & tight.
Source of Error: Rheostat may have high resistance. The instrument screws may be loose.
EXPERIMENT – 2
Aim: To find resistance of a given wire using Whetstone’s bridge (meter bridge) & hence determine the specific resistance of the material. Apparatus: A meter bridge (slide Wire Bridge), a galvanometer, a resistance box, a laclanche cell, a jockey, a one- way key, a resistance wire, a screw gauge, meter scale, set square, connecting wires and sandpaper.
Formulae Used: (i) The unknown resistance X is given by:
X = R
l
l
Where,
R = known resistance placed in left gap. X = Unknown resistance in right gap of meter bridge. l =length of meter bridge wire from zero and upto balance point (in cm)
(ii) Specific resistance ( ) of the material of given wire is given =
L
X D
^2
Where, D : Diameter of given wire L : Length of given wire.
EXPERIMENT – 3
Aim: To verify the laws of combination (series & parallel) of resistances using meter bridge (slide Wire Bridge) Apparatus: A meter bridge, laclanche cell, a galvanometer, a resistance box, a jockey, two resistances wires, set square, sand paper and connecting wires.
Observations: Table for length (l) & unknown resistance (r):
Resistant Coil Obs. No.
Resistance from resistance box, R (ohm)
Length AB = l (cm)
Length BC = 100 – l (cm)
Resistance
r = R
l
l
Mean Resistant (ohm)
r 1 only
r 2 only
r 1 & r 2 in series
r 1 & r 2 in parallel
Calculations:
(i) In Series: Experimental value of RS = 2.72
Theoretical value of RS = r 1 + r 2 = 2.75
(ii) In parallel: Experimental value of RP = 0.66
Theoretical value of RP =
1 2
12
r r
rr
Result: Within limits of experimental error, experimental & theoretical values of RS are same. Hence the law of resistance in series i.e. RS = r 1 + r 2 is verified. (1) Within limits of experimental error, experimental & theoretical
values of RP are same. Hence law of resistances in parallel i.e. RS = 1 2
12
r r
rr
is verified.
Precautions: (i) The connections should be neat, clean & tight. (ii) Move the jockey gently over the wire & don’t rub it. (iii) All plugs in resistant box should be tight.
Sources of Error: (i) The plugs may not be clean. (ii) The instrument screws maybe loose.
EXPERIMENT – 4
Aim: To determine the resistance of a galvanometer by half-deflection method & to find its figure of merit.
Apparatus: A Weston type galvanometer, a voltmeter, a battery, a rheostat, two resistance boxes (10,000 and 500
), two one-way keys, a screw gauge, a meter scale, connecting wires and a piece of sandpaper.
Formulae Used: (i) The resistant of the given galvanometer as found by half-deflection method:
G =
R S
R S
Where R: resistance connected in series with the galvanometer S: shunt resistance
(ii) Figure of merit: k = ( R G )
E
Where E : emf of the cell
: deflection produced with resistance R.
Calculation: Mean G = 70.8
(i) For G : Calculate G using formula. Take mean of all values of G recorded in table. (ii) For k: Calculate k using formula & record in table. Take mean of values of k. Result:
S =
G 0. 0155
I I
I
o G
G
* Computing the length of the wire to make resistance of 0.155
b) Observations for diameter of the wire: (i) Pitch of screw gauge, p = 1 mm (ii) No. of division of circular scale = 100 (iii) Least count, a = 0.01 mm (iv) Zero error, e = 0.0 mm (v) Diameter of the wire = 0.98 mm, Radius = 0.049 cm
c) Specific resistance of material of wire, 1. 92 10 ^6 cm
d) Required length of the wire,
l S ^^ r^2 =
6
2
cm = 60.8 cm
Verification: Checking the performance of the converted ammeter: Current indicated by full scale deflection (No) of converted ammeter. Io = 3A
Least count of converted ammeter, k’^ = 0. 1 A / div.
N
I
o
o
Result:
Current IG for full scale deflection = 6.57 x 10 -4^ A
Resistance of shunt required to convert the galvanometer into ammeter, S = 0.0155
Required length of wire, l = 60.8 cm
As error l’^ – l is very small, conversion is verified.
Precautions & Sources of Error: (i) All connections should be neat & tight. (ii) The diameter of the wire for making shunt resistance should be measured accurately for diameter is taken in two mutually perpendicular directions. (iii) The terminal of the ammeter marked positive should be connected to positive pole of the battery. Also ammeter should be in series with circuit.
EXPERIMENT – 6
Aim: To find the value of v for different values of ‘u’ in case of a concave mirror & to find its focal length. Apparatus: An optical bench with three uprights. Concave mirror, a mirror holder, two optical needles, a knitting needle & a half – meter scale.
Formulae Used: The mirror formula is:
f u v
(^1) (^1) 1
We have, f =
u v
uv
Where, f = focal length of concave mirror. u = distance of object needle from pole of mirror. v = distance of image needle from pole of mirror.
Observation: Rough focal length of given concave mirror = 10.9 cm Actual length of the knitting needle, x = 15 cm
Observed distance between the mirror & object needle when knitting needle is placed between them, y = 15.2 cm. Observed distance between the mirror & image needle when knitting needle is placed between them, z = 15.8 cm. Index error for u , e 1 = y – x = – 0.2 cm Index error for v , e 2 = z – x = – 0.8 cm
Sr. No.
Position Corrected Distance (^) 1/ u (cm-^1 )
1/ v Mirror P (cm)^ Concave Needle O^ Object Needle I^ Image u^ PO cm v cm^ PI^ (cm-^1 ) 1 0.0 18 26 17.8 25.2 0.056 0. 2 0.0 17 30.3 16.8 29.5 0.06 0. 3 0.0 16 33.4 15.8 32.6 0.063 0. 4 0.0 26 18 25.8 17.2 0.038 0. 5 0.0 30.3 17 30.1 16.2 0.033 0. 6 0.0 33.4 16 33.2 15.2 0.030 0.
Calculations: (i) u – v graph: Explanation: from mirror formula applied to point A:
f u v
(^1) (^1) 1
As u = v, 2 2
(^1 22) andf uorv v
or f u
Hence, f = OD^ 10. 5 cm
Graph Scale: X’ axis: 1 cm = 5 cm of u Y’ axis: 1 cm = 5 cm of v
Also f = OB^ 10. 5 cm
Mean value of f = -10.5 cm
(ii)^1 1 graph :
v
and
u
The focal length, f = cm OA OB
Graph Scale: X’ axis: 1 cm = 0.01 cm-1^ of
u
Y’ axis: 1 cm = 0.01 cm-1^ of
v
Result: The focal length of the given concave mirror: (i) From u – v graph is : f = – 10.5 cm
(ii) From
u v
1 ^1 graph is: f = – 10.47 cm
Precautions: (i) The uprights should be vertical. (ii) Tip-to-tip parallax should be removed between the needle I and image of needle O. (iii) To locate the position of the image the eye should be at least 30 cm away from the needle. **Sources of Error: *** The uprights may not be vertical. * Parallax removal may not be perfect
EXPERIMENT – 8
Aim: To find the focal length of a convex lens by plotting a graph:
(i) between u and v
(ii) between
v
and
u
Apparatus: An optical bench with three uprights, a convex lens, lens holder, two optical needles, a knitting needles & a half-metre scale.
Formula Used:
The relation between u, v and f for convex lens is:
f v u
Where f: focal length of convex lens
u: distance of object needle from lens’ optical centre.
v: distance of image needle from lens’ optical centre.
Observations:
(i) Rough focal length of the lens = 10 cm (ii) Actual length of knitting needle, x = 15 cm. (iii) Observed distance between object needle & the lens when knitting needle is placed between them, y = 15.2 cm. (iv) Observed distance between image needle & the lens when knitting needle is placed between them, z = 14.1 cm. (v) Index correction for the object distance u, x – y = – 0.2 cm (vi) Index correction for the image distance v, x – z = +0.9 cm
Observation Table:
S. No.
Position of: (cm) Object u (cm) v (cm) 1/v (cm-^1 ) 1/u (cm-^1 ) needle Lens^
Image needle 1 66 50 26 16 24 0.041 0. 2 67 50 27 17 23 0.043 0. 3 68 50 28 18 22 0.045 0. 4 70 50 30 20 20 0.05 0. 5 75 50 33 23 17 0.058 0. 6 80 50 34 24 16 0.062 0.
Calculation of focal length by graphical method: (i) u – v graph: The graph is a rectangular hyperbola: Scale: X’ axis: 1 cm = 5 cm of u Y’ axis: 1 cm = 5 cm of v AB = AC = 2 f or OC = OB = 2 f
^ f =
OC
andalsof
OB
Mean value of f = 10.1 cm.
(ii) :
graph
u v
The graph is a straight line.
Scale; X’ axis: 1 cm = 0.01 cm-1^ of
u
Y’ axis: 1 cm = 0.01 cm-1^ of
v
Focal length, f =^1 110. 2 cm.
OP OQ
Result:
(i) From u-v graph is, f = 10.1 cm
(ii) From
u v
1 ^1 graph is, f = 10.2 cm
Precautions:
(i) Tips of object & image needles should be at the same height as the centre of the lens. (ii) Parallax should be removed from tip-to-tip by keeping eye at a distance at least 30 cm. away from the needle. (iii) The image & the object needles should not be interchanged for different sets of observations.
EXPERIMENT – 10
Aim: (i) To determine angle of minimum deviation for a given prism by plotting a graph between angle of incidence & angle of deviation. (ii) To determine the refractive index of the material (glass) of the prism. Apparatus: Drawing board, a white sheet of paper, prism, drawing pins, pencil, half metre scale, office pins, graph paper & protector.
Formulae Used:
The refractive index, of the material of the prism is given by:
sin 2
sin 2 A
A Dm ^ Where Dm^ is the angle of minimum deviation & A is the angle of prism.
Calculations:
From graph between angle of incidence, i and angle of deviation, we get the value of Dm (angle of minimum
deviation): Dm = 37.8o
Thus,
^ sin 2
sin 2 A
A Dm
o
o
sin 30
sin^97.^8
Result:
(i) From i D graph we see that as i increases, D first decreases, attains a minimum value (Dm) & then again
starts increasing for further increase in i.
(ii) Angle of minimum deviation = Dm = 37.8o (iii) Refraction index of material of prism, 1. 5077
Precautions: (i) The angle of incidence should be between 30o^ – 60 o. (ii) The pins should be fixed vertical. (iii) The distance between the two pins should not be less than 8 cm.
Sources of Error: (i) Pin pricks may be thick. (ii) Measurement of angles maybe wrong.
EXPERIMENT – 11
Aim: To determine the refractive index of a glass using travelling microscope.
Apparatus: A marker, glass slab, travelling microscope, lycopodium powder.
Formulae Used:
Refractive index 2 1
3 1
r r
r r
apparentdepth
realdepth
Observations:
Least count of travelling microscope = 0.001 cm or 0.01 mm Mean values: r 1 = 0 mm r 2 = 6.81 mm r 3 = 10.25 mm
Observations: Reading of Microscope focused on:
S. No. (^) rMark without slab 1 = M + n x LC min
Mark with slab on it r 2 = M + n x LC min
Powder on top of slab R 3 = M + n x LC min 1 0 6.5 + 29 x 0.01 = 6.79mm 10 + 23 x 0.01 = 10.23mm 2 0 6.5 + 31 x 0.01 = 6.81mm 10 + 25 x 0.01 = 10.25mm 3 0 6.5 + 33 x 0.01 = 6.83mm 10 + 27 x 0.01 = 10.27mm
Calculations: Real depth = dr = r 3 – r 1 = Mean dr = 10.25 mm Apparent depth = da = r 2 – r 1 Mean da = 6.81 mm
Refractive index,
a
r
d
d
apparentdepth
real^ depth 1. 52
Result:
The refractive index of the glass slab by using travelling microscope is determined as 1.52 =
Precautions:
(i) Microscope once focused on the cross mark, the focusing should not be disturbed throughout the experiment. Only rack and pinion screw should be turned to move the microscope upward. (ii) Only a thin layer of powder should be spread on top of slab. (iii) Eye piece should be so adjusted that cross-wires are distinctly seen.
Calculations:
Graph is plotted between forward – bias voltage (VF) (on x-axis) and forward current, IF (on y – axis) Scale: X – axis: 1 cm = V of VF Y – axis: 1 cm = mA of IF Graph is plotted between reverse bias voltage, VR (along X’ axis) and reverse current, IR (along Y’ axis).
Scale: X’ axis = 1 cm = V of VR Y’ axis = 1 cm = A of IF
Result: The obtained curves are the characteristics curves of the semi-conductor diode.
Precautions: (i) All connections should be neat, clean & tight. (ii) Key should be used in circuit & opened when the circuit is not being used. (iii) Forward bias voltage beyond breakdown should not be applied. Sources of error: The junction diode supplied maybe faulty.
NOTE: Beside Practical File ONE Activity file with SIX Activities (A-3, A-4, A-6 and B-8, B-11, B-12 From Any Physics Practical File) and ONE Project Report has to be made by
each student from the Elite Manual.
