INDIAN LEARNER’S OWN ACADEMY -...

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INDIAN LEARNER’S OWN ACADEMY

KUWAIT

CLASS XII

PHYSICS PRACTICAL

ROUGH RECORD OF OBSERVATIONS

2018-19

NAME OF THE STUDENT:___________________________

CLASS : XII A

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General Instructions for Physics Practical

You will perform 15 experiments (7 from Section A and 8 from Section B)

during this academic year.

Always be in the group assigned to you.

You must bring your observation book while entering the lab.

Come prepared for performing the practical. Know the aim, apparatus

required, procedure and theory of the practical which you are going to

perform in the class.

Prepare your practical record with all entries [Aim, Materials required,

Theory , Procedure, Result, Precautions and Sources of error(on the RHS)

and Circuit Diagram/ Ray Diagram, Observations, Tabular Columns and

Expected shape of the graph, if any (on the LHS)], before the experiment is

conducted.

Follow the verbal and written instructions strictly while performing the

experiment. Do not perform anything which is not a part of the standard

procedure. When in doubt, ASK, do not assume things.

Tabulate your observations only in your observation note book and not on

loose or rough sheets.

Calculations should be neatly done in the space provided in the observation

book and all values must be written in ink.

Get the result of your experiment signed in your observation book on the

same day of the experiment or latest by the next working day.

Once the experiment is signed in your observation book, you may complete

your record for that experiment. Do not enter the values in your record

until it has been checked by the teacher in your observation book.

You must bring the completed record for correction when you come for

the next practical.

Follow the lab safety rules strictly.

Leave the lab neater than you found while entering.

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General Instruction for Physics Investigatory Project

It is mandatory for all the students to do any one investigatory project based

on class XII physics curriculum.

You may do it individually or form groups of maximum two students from

your class.

Topic for the project must be finalized and the hard copy of the first

draft of the project shall be submitted to the teacher by the first week of

April 2019.

You shall not change your project once it is approved.

For projects done in group, a group need to submit only a single copy of the

draft. However they have to submit individual final report at the end of the

project.

Students have to make their own arrangement for apparatus and equipment

for their project.

All have to work on your project before/ during the summer vacation

and shall complete the investigatory part by August 2019.

A soft copy of the project report must be given to the teacher, for any

necessary corrections, before taking the final print.

The final report of the project work with the working model must be

ready by the last week of August 2019.

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INDEX

SL.NO DATE BRIEF AIM REMARK SIGNATURE

SECTION A

1 To determine resistance per cm of a given wire by

plotting a graph for potential difference versus current.

2

To find resistance of a given wire using metre bridge

and hence determine the resistivity (specific resistance)

of its material.

3 To verify the laws of combination (series) of resistances

using a metre bridge.

4 To verify the laws of combination (parallel) of

resistances using a metre bridge.

5 To compare the EMF of two given primary cells using

potentiometer.

6 To determine resistance of a galvanometer by half-

deflection method and to find its figure of merit.

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To convert the given galvanometer (of known

resistance and figure of merit) into a voltmeter of

desired range and to verify the same.

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Experiment – 1

Ohm’s Law

Date of experiment:--------------------------

Aim: To determine resistance per cm of a given wire by plotting a graph for potential difference

versus current.

Apparatus Required: A resistance wire, a voltmeter (0-3) V and an ammeter (0-3) A of

appropriate range, a battery eliminator, a rheostat, a metre scale, one way key and connecting

wires.

Theory:

According to the Ohm’s law the current flowing through a conductor is directly proportional to

the potential difference across its ends provided the physical conditions of the conductor remains

the same. If I be the current flowing through a conductor and V be the potential difference across

its ends, then according to, Ohm’s Law,

V α I

V = IR

where the constant of proportionality R is the resistance of the conductor. The slope of V-I graph

gives R.

Procedure:

1. Make neat, clean and tight connections according to the circuit diagram.

2. Determine the least count of voltmeter and ammeter, and also note the zero error, if any.

3. Insert the key K and the readings in the voltmeter and ammeter.

4. Repeat the observations five times for different positions of the rheostat.

5. Taking current on X-axis and voltage on Y-axis and suitable scale, plot the straight line

graph passing through the origin.

6. The slope of the graph gives the resistance of the wire.

7. Measure the length of the wire using a metre scale.

8. Calculate the resistance per unit length of the wire.

Result: Resistance per cm of the wire is ____________ Ω/cm.

Sources of error:

1. The instrument screws may be loose.

2. Thick connecting wires may not be available.

3. Rheostat may have high resistance.

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Precautions:

1. The connections should be neat, clean and tight.

2. Thick copper wires should be used for the connections after removing the insulations

near their ends by rubbing with sand paper.

3. Voltmeter and ammeter should be of proper range.

4. A low resistance rheostat should be used.

5. The key should be inserted only while taking observations to avoid heating of resistance

Circuit Diagram

Expected Shape of Graph :

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Observation:

Least count of the Ammeter:________

Least count of the voltmeter:________

Length of the wire:___________

Observation Table:

Sl.no Ammeter Reading I (in A) Voltmeter Reading V (in V)

1

2

3

4

5

Calculations:

R from graph =slope = ________Ω

Resistance per cm =___________Ω/cm

Teacher’s Signature: …………………………….

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Experiment No: 2

MeterBridge I

Date of Experiment ………………….

Aim: To find resistance of a given wire using metre bridge and hence determine the resistivity

(specific resistance) of its material.

Apparatus: Metre bridge, Battery eliminator, Galvanometer, Resistance box, Jockey, One way key, A

resistance wire, Screw gauge, Metre scale and Connecting wires

Theory :

If the length AB is , then the length BC is ( 100-l ).

Then, according to Wheatstone’s principle;

Now, the unknown resistance can be calculated as,

The specific resistance or resistivity of the material of the wire can be then calculated by using the relation,

Where L be the length of the wire and r be its radius.

Procedure:

1. Make the connections as per the connections diagram.

2. Connect the resistance wire in the left gap and resistance box in the right gap.

3. Introduce some resistance in the circuit by taking out some resistance from the resistance box.

4. Plug the key. Bring the jockey in contact with the end A first, and then with C. Note the deflection on

the galvanometer.

5. If the galvanometer deflects in the opposite direction, the connections are right and the null point is in

between A and C.

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6. Now, slide the jockey slowly over the wire starting from one end till the balancing point is reached.

Note the balancing length ‘l’

7. Repeat the process for different values of R. The balancing length is measured each time.

8. We can calculate the unknown resistance of the resistance wire by using the relation,

9. Measure the diameter of the given resistance wire using a screw gauge. Hence, its

radius(r) can be found.

10. Also measure the length (L) of the wire using a metre scale.

11. From the measured values, the specific resistance (resistivity) of the given resistance wire

can be calculated

Result : The resistance of the wire = __________Ω

The resistivity of the material = _________ Ωm

Sources of error:

1. The wire may not be of uniform cross section

2. The end resistances may not have been considered

3. The screw guage may have backlash error

Precautions:

1. The plugs in the resistance box should be tight

2. The balance point or null point should preferably be between 40 cm and 60 cm.

3. The jockey should not be pressed on the wire.

4. The plug in the key should be inserted only when you record observation, to avoid

heating of the bridge wire.

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Circuit Diagram:

Observations:

a) To find unknown resistance X

Sl.No R (from the resistance

box)Ω

Balancing length (l)

cm

(100-l)

cm

1

2

3

4

5

Mean X = ____________ Ω

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b) To find the diameter of the wire using screw guage

Least count = __________mm

Zero error = ____________

Sl. No L.S.R H.S.R Observed diameter

(LSR+HSR x LC) mm Corrected diameter

1

2

3

4

5

Mean d= ________ mm

Radius = _________ mm = __________ m

Length of the wire = ________cm = ________m

= __________ Ωm

Teacher’s signature ………………………….

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Experiment No. 3

Meter Bridge –II

Date of the experiment : ________________

Aim :- To verify the laws of combination (series) of resistances using a metre bridge.

Apparatus :- Metre bridge, Battery eliminator, Galvanometer, Resistance box, Jockey, One way key,

two resistance wire, and Connecting wires

Theory:-




Where R is the resistance taken out from the resistance box.

Equivalent resistance of two resistors connected in series, Rs = R1 + R2

Procedure:-

1. Make connections as shown in the circuit diagram, connecting a resistance box in one

gap and the first unknown resistance R1 in the other.

2. Introduce some resistance in the circuit by taking out some resistance from the resistance

box.

3. Plug the key. Bring the jockey in contact with the end A first, and then with C. Note the

deflection on the galvanometer.

4. If the galvanometer deflects in the opposite direction, the connections are right and the

null point is in between A and C.

5. Now, slide the jockey slowly over the wire starting from one end till the balancing point

is reached. Note the balancing length ‘l’

6. Calculate the unknown resistance using the formula.

7. Repeat the experiment with R2 in place of R1, then with series combination of R1 and R2.

8. Calculate the equivalent resistance in series using the measured values of R1 and R2 and

compare the measured values of the series combinations.

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Result:-

Resistance R1 = _________Ω

Resistance R2 = __________Ω

Value of Rs using the formula = __________Ω

Value of Rs from the experiment = __________Ω

% Error = ___________

Within the experimental limits the measured values of Rs are the same as the theoretical

value, hence proving the laws of combination of resistances in series.

Sources of error:



Precautions:






Circuit Diagram :

series :

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Observations

Sl.No

R (from the

resistance

box)Ω

Balancing

length (l) cm (100-l) cm

1

2

3

Mean Value of R1=

1

2

3

Mean Value of R2=

1

2

3

Mean Value of Rs=

Value of Rsfrom the formula Rs=R1+R2= ___________ Ω

Value of Rsfrom the experiment = __________Ω

% erro = __________

Teacher’s Signature …………………………

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Experiment No. 4

Meter Bridge –III

Date of the experiment : ________________

Aim :- To verify the laws of combination (parallel) of resistances using a metre bridge.

Apparatus :- Metre bridge, Battery eliminator, Galvanometer, Resistance box, Jockey, One way key,

two resistance wire, and Connecting wires

Theory:-




Where R is the resistance taken out from the resistance box.

Equivalent resistance of two resistors connected in parallel,

=

+

Procedure:-

1. Make connections as shown in the circuit diagram, connecting a resistance box in one

gap and the first unknown resistance R1 in the other.

2. Introduce some resistance in the circuit by taking out some resistance from the resistance

box.

3. Plug the key. Bring the jockey in contact with the end A first, and then with C. Note the

deflection on the galvanometer.

4. If the galvanometer deflects in the opposite direction, the connections are right and the

null point is in between A and C.

5. Now, slide the jockey slowly over the wire starting from one end till the balancing point

is reached. Note the balancing length ‘l’

6. Calculate the unknown resistance using the formula.

7. Repeat the experiment with R2 in place of R1, then with parallel combination of R1 and

R2.

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8. Calculate the equivalent resistance in parallel using the measured values of R1 and R2 and

compare the measured values of the parallel combinations.

Result:-

Resistance R1 = _________Ω

Resistance R2 = __________Ω

Value of Rp using the formula = __________Ω

Value of Rp from the experiment = __________Ω

% Error = ___________

Within the experimental limits the measured values of Rp are the same as the theoretical

value, hence proving the laws of combination of resistances in parallel.

Sources of error:



Precautions:






Circuit Diagram :

parallel :

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Observations

Sl.No

R (from the

resistance

box)Ω

Balancing

length (l) cm (100-l) cm

1

2

3

Mean Value of R1=

1

2

3

Mean Value of R2=

1

2

3

Mean Value of Rp=

Value of Rpfrom the formula = ___________ Ω

Value of Rpfrom the experiment = __________Ω

% erro = __________


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Experiment No-5

Potentiometer

Date of the experiment:…………………….

Aim :- To compare the EMF of two given primary cells using potentiometer.

Apparatus :- Potentiometer, Daniel cell, Leclanche cell, Jockey, Battery eliminator, Resistance box,

Galvanometer, One way key, Two way key, Rheostat and Connecting wires

Theory:- The potentiometer works on the principle that when a constant current flows through a wire of

uniform cross sectional area, potential difference between its two points is directly proportional to the

length of the wire between the two points.

or, ; where k is the potential gradient along the wire.

Thus it is possible to compare the emf’s of two given cells by measuring the respective balancing lengths

l1 and l2

and

Or,

Procedure :-

1. Arrange the required materials on a table and make the connections as per the connection

diagram.

2. To test the connection, insert plug in the one way key k1 and also in between the terminals a and

c of the two way key. Introduce a sufficiently high resistance on the resistance box (R.B). Place

the jockey at the two end points of the wire. Press the jockey at both end of the potentiometer

wire and note the deflection in galvanometer. If the galvanometer shows opposite deflection, the

connections are correct.

3. Now, gently slide the jockey along the potentiometer wire and stop when null point is obtained.

4. Measure the length l1 between this point and the end P of the potentiometer. It is the balancing

length for the cell E1.

5. Disconnect the cell E1 by removing the plug from the gap ac of the two way key and connect the

cell E2 by inserting plug into the gap bc of the two way key.

6. Again slide the jockey along the potentiometer wire to obtain the null point. Measure the new

balancing length l2 for the cell E2 based on this point.

7. Repeat the experiment adjusting the rheostat and record the observations.

8. Each time, the ratio between the emf’s of the given cells can be calculated using the relation,

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Result :- The ratio ________

Sources of error:

1. There may be some contact resistance at the ends of the wire.

2. The heating of the potentiometer wire may cause some error

3. Potentiometer wire may not be of uniform cross section

4. Error in detecting null deflection in the galvanometer

Precautions:

1. The jockey should not be pressed along the potentiometer wire.

2. The emf of the auxiliary battery in the potentiometer circuit should be greater than the emf of the

primary cells.

3. The current should be adjusted to obtain a considerably large balancing length.

Circuit Diagram

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Observations

Sl.No Balancing Length

Leclanche Cell

l1 cm

Daniel Cell

l2 cm

1

2

3

4

5

Mean ratio of emfs = ______________


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Experiment No-6

Galvanometer-Figure of merit

Date of the experiment:…………………………..

Aim: To determine resistance of a galvanometer by half-deflection method and to find its figure of merit.

Apparatus:- A weston type galvanometer, A battery or battery eliminator, Two resistance boxes, Two

one-way keys and Connecting wires.

Theory:-

The figure of merit of a galvanometer is the current required to produce a deflection of one division in the

galvanometer scale. It is represented by the letter k, and is given as,

If the deflection in the galvanometer is θ when the resistance R is connected in series to the galvanometer

and θ/2 when the shunt resistance S is also connected, then the resistance of the galvanometer,

Procedure:-

a) Resistance of galvanometer by half deflection method :

1. Arrange the components on a table and connect them as per the circuit diagram.

2. Take out a high resistance from the resistance box 1 and insert the key k1.

3. Adjust the resistance from this resistance box to get maximum galvanometer deflection.

4. Note the deflection and record it as θ in the tubular column.

5. Insert the key k2 also, without changing the value on the resistance box.

6. Now, adjust the resistance from the low resistance box such that galvanometer shows deflection

which is exactly half of the previous reading.

7. Record the value of low resistance box.

8. We can repeat the experiment by changing the value of high resistance R and adjusting low

resistance S.

9. The resistance of the given galvanometer can be calculated each time by using the relation

G=RS/(R-S).

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b) Figure of merit of the galvanometer :

1. Release key k2 from the connection. Insert key k1.

2. Adjust the value of R such that the galvanometer shows a certain deflection.

3. Record the observations in a tabular column.

4. Repeat the experiment by changing the value of R and note the galvanometer deflection each

time.

5. We can find the figure of merit of the galvanometer by using the equation, k= E/(R+G)θ.

Result:- 1. The resistance of the given galvanometer is ………..Ω

2. The figure of merit of the galvanometer is ………… A/div

Sources of error:-

1. The plugs of the resistance box may not be tight

2. The divisions on the galvanometer may not be evenly graduated.

Precautions:-

1. All the connections should be neat, clean and tight

2. The deflection in the galvanometer before connecting the shunt should be even number of

readings.

3. The value of R should be large to keep the deflection within the scale.

Circuit Diagram

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Observations:

Emf of the battery eliminator = ………. V

Sl.

No

Resistance

R

Deflection

θ

Shunt

Resistance S

Half

deflection θ/2

1

2

3

4

Mean Value of G =---------------------- Ω

Mean Value of K = -----------------------A/div


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Experiment -7

Galvanometer – Voltmeter

Date of experiment:………………………

Aim : - To convert the given galvanometer (of known resistance and figure of merit) into a voltmeter of

desired range and to verify the same.

Apparatus :- A Weston type galvanometer of known resistance and figure of merit, a battery, a rheostat,

one-way key, A resistance box of the range 0 to 10,000 ohm, a voltmeter of 0-3 volt range, connecting

wires

Theory

A galvanometer can be converted into a voltmeter of desired range by connecting a suitable high

resistance R in series with the galvanometer. Let G is the resistance of the galvanometer which gives full

scale deflection when Ig current flows through it. Let V is the range of the voltmeter, the series resistance

R required for the conversion is given by,

Procedure:-

1. Note down the given value of galvanometer resistance G and its figure of merit K. Also note the

total number of divisions n on either side of the zero of the galvanometer. Complete the value of

Ig with the help of the relation, Ig = Nk. Calculate the value of required series resistance R to be

connected in series with the galvanometer for the conversion of the given galvanometer into

voltmeter of the given range

2. Connect the resistance box of range 0 to 10,000 ohm in series with the galvanometer and take out

the plugs of resistance R from it. Now galvanometer with this resistance in series is converted

into voltmeter of the given range V volt.

3. For verification of the converted voltmeter, make the connections shown in the circuit diagram.

4. Take out the plugs of calculated resistance R from the resistance box of the range 0 to 10,000

ohm and insert the key K and adjust the rheostat so that the deflection in galvanometer becomes

maximum.

5. Note the readings of standard voltmeter and galvanometer.

6. Convert the galvanometer reading into volt and find the difference between them, if any. This

difference gives the error.

7. Take the four observations more by changing the resistance with the help of the rheostat over the

whole range of the voltmeter. Record all the observations in the table.

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Result:-

The value of required high resistance = ________Ω

The value of the current for full scale deflection, Ig = ________A

Hence, conversion of the given galvanometer into voltmeter of the given range is verified.

Precautions:-

1. All the connections should be neat, clean and tight.

2. All the plugs in both of the resistance boxes should be tight.

3. First the high resistance R from the resistance box should be introduced, then the battery key K1

plug should be inserted to avoid any damage to the galvanometer.

4. The e.m.f. of the battery should be constant.

5. The value of R should be large as compared to G.

Circuit Diagram

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Observations:-

Given resistance of the galvanometer, G = _______Ω

Given value of the figure of merit of the galvanometer, K = ________amp/division

Total number of divisions on either side of the zero of the galvanometer, n = ________divisions

Current for full scale deflection, Ig = nK = ________A.

Range of conversion of the converted voltmeter, V = _______V

Value of the required series resistance, R = __________Ω

Least count of the converted voltmeter = 𝑉 𝑛 = _______V

Least count of the standard voltmeter = _________ V

Observation Table:

Sl.No Reading of Converted Voltmeter

Standard Voltmeter Reading V2 (Volts) Error (V2- V1) Deflection θ PD V1 = θ x LC

1

2

3

4

5

Mean Error = ____________

Teacher’s Signature ………………………………………

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