Internal Resistance Of a Given Primary Cell Using a Potentiometer


To determine the internal resistance of a given primary cell using a potentiometer.


A potentiometer, a battery (or battery eliminator), two one-way keys, an id resistance, a galvanometer, a high resistance box, a fractional resistance box, an ammeter,  voltmeter, a cell (say Leclanche cell), a jockey, a set square, connecting wires and sandpaper.




When Key K2 is open and K1 is closed,
Let null point be obtained at a distance l1 from A
Therefore E = Kl1 –> (1)
When Key K2 is closed and K1 is open,
Let null point be obtained at a distance l2 from A
Therefore V = Kl2 –> (2)
(1) divided by (2)
E/V = l1/l2
(S+r)/S  = l1/l2
r = S*(l1-l2)/l2

Where S : the shunt resistance in parallel with given cell.
l1 and l2 : Balancing lengths without and with shunt respectively.
r : internal resistance of the cell.


  1. Make the connections as shown in circuit diagram.
  2. Clean the ends of the connecting wires with sandpaper and make tight connections. Tighten the plugs of the resistance box.
  3. Check the E.M.F. of the battery and cell and see that E.M.F. of the battery is more than that of the given cell otherwise null or balance point won’t be obtained. (E’ > E)
  4. Take maximum current from the battery, making rheostat resistance small.
  5. Insert the plug in Key K1 and adjust the rheostat so that a null point is obtained or the fourth wire of potentiometer.
  6. Insert the 2000 Ohm plug in its position in resistance box and obtain a null point by slightly adjusting the jockey.
  7. Measure the balancing length L1.
  8. Take out the 2000 Ohm plug from the resistance box. Introduce the plugs in Key K1, as well as in Key K2. Take act a small resistance from the resistance box R connected in parallel with the cell. Slide the jockey along the potentiometer wire and obtain a null point. Insert the 2000 Ohm plug back in its position in R.B. and make a further adjustment for a sharp null point.
  9. Insert the 2000 Ohm plug back in its position in R.B. and make a further adjustment for a sharp null point.
  10. Measure the balancing length l2 from end P.
  11. Remove the plugs keys K1 and K2. Wait for some time and respect the activity for the same current.
  12. Record your observations.


  • Range of voltmeter
  •  Least count of voltmeter
  •  E.M.F. of battery (or battery eliminator)
  •  E.M.F. of cell





The internal resistance of the given cell is…………… ohm.



  1. The e.m.f. of the battery should be greater than that of the cell.
  2. For one set of observation, the ammeter reading should remain constant.
  3. Current should be passed for a short time only while finding the null point.



You can also get Class XII Practicals on BiologyPhysics, and Physical Education.

Viva Voce – Questions on Protein, Fat, Carbohydrate Test

  • What are proteins? Name their basic unit.

Proteins are complex nitrogenous organic compounds of high molecular masses. Amino acids are the basic unit of proteins.

  • What is the ring due to in Molisch’s test?

Concentrated sulphuric acid (H2SO4) produces furfural or its derivative on reacting with carbohydrates.  This furfural forms a violet coloured compound on coupling with naphthol.

  • What is the chemistry of Acrolein Test?

Oil or fat gets hydrolyzed to free glycol which forms pungent smelling acrolein on further reaction.

Chemical Equation of Acrolein Test
Chemical Equation of Acrolein Test

You can also get Class XII Practicals on BiologyPhysics, and Physical Education.

Viva Voce – Questions on Preparation of Sols

  • What is a sol?

Sol is a colloidal suspension of a solid in a liquid.

  • What is the criteria for classifying sols? What type of sols are known?

Sols are classified based on their affinity for the dispersed phase for the dispersion medium. There are types of sols – lyophobic and lyophilic.

  • What is the difference between lyophilic and lyophobic sol?

A sol in which colloidal particles have an affinity for the dispersion medium is called lyophilic sol whereas, in a lyophobic sol, colloidal particles have no or very little affinity for the dispersion medium.

  • What is meant by ‘dialysis’?

The phenomena of purification of sols by passing through a semipermeable membrane is known as dialysis.

  • What is the special characteristic of the paper used in dialysis?

It only permits the electrolyte to pass through it and doesn’t allow the passage of colloidal particles.

  • What is the nature of charge on (i) ferric hydroxide and (ii) arsenious sulphide sols?

Ferric hydroxide sol is positively charged whereas arsenious sulphide is negatively charged.

You can also get Class XII Practicals on BiologyPhysicsChemistry, and Physical Education.

Viva Voce – Questions on Chromatography

  • What is chromatography?

It is a rapid and efficient technique for separating various components of a mixture.

  • What is a chromatogram?

The paper strip after running of the solvent and drying is called chromatogram.

  • What are the moving and stationary phases in paper chromatography?

Both phases are liquid. The solvent is the mobile on moving phase while the water absorbed in the pores of the paper acts as a stationary phase.

  • Why should the strip not touch the walls of the jar?

That is necessary to avoid the uneven flow of the developing solvent.

  • What do you understand by ‘Rf’?

Rf (Retention Factor) is the ratio of the distance travelled by the component from the origin line and distance travelled by solvent from origin line.

  • Why is the rate of movement of mobile phase less in ascending paper chromatography?

This is because the mobile phase moves against gravity.

You can also get Class XII Practicals on BiologyPhysics, and Physical Education.

Viva Voce – Questions on Salt Analysis Practicals

  • What is qualitative analysis?

The type of analysis that deals with the methods which are used to determine the constituents of a compound.

  • What is a radical?

A radical may be defined as an atom or group of atoms which carry charge & behaves like a single unit in chemical reactions.

  • What are preliminary tests?

The tests which are done for getting an indication of the radicals are called preliminary tests.

  • Name a few preliminary tests.

Physical examination of salt, dry heating, the action of diluted and concentrated sulphuric acid (H2SO4).

  • Which radicals are absent in a white salt?

Copper – Cu2+, Iron(II)-  Fe2+,  Iron(III) – Fe3+,  Cobalt – Co2+, and Nickel – Ni2+

  • Can sulphuric acid (H2SO4) be used for preparing the original solution?

No, because sulphuric acid (H2SO4) will produce sulphates of the cations and some sulphates like lead sulphate (PbSO4) are insoluble. So, we may not get the required clear original solution.

  • Explain how Aluminium (III) [Al3+] can be confirmed using cobalt nitrate.

Take a salt solution and add cobalt nitrate to it. Burn a filter paper which has been dipped into this solution. If you detect blue colour on black ash of filter paper, Aluminium (III) [Al3+] confirmed.

  • Why is ammonium chloride [NH4Cl] in III group? Can we add ammonium hydroxide (NH4OH) first?

NH4Cl is added to prevent precipitation of radicals other than III group as hydroxides by common ion effect. If we add NH4OH first, radical of group IV, V & VI will also precipitate and accordingly we cannot do it.

  • Why is it essential to boil off hydrogen sulphide [H2S] gas before precipitating III group?

If H2S isn’t boiled off group IV cations will also get precipitated.

  • How does the addition of ammonium hydroxide (NH4OH) help in precipitation of cations as sulphides?

Solubility product of Group IV sulphides is greater than those of group IV radicals. Thus, a higher concentration of S2- ions are required to precipitate Group IV radicals as sulphides. OH ions of ammonium hydroxide (NH4OH) with H+ ions of H2S, shift the equilibrium towards right or increasing the concentration of S2- ions.

  • Black precipitates in Group IV indicate which cations?

Presence of either Ni2+ or Co2+.

  • Why can sodium hydroxide [NaOH] not be used instead of ammonium chloride [NH4Cl] and ammonium hydroxide (NH4OH)?

NaOH is a very strong electrolyte and its ionization cannot be supressed. Moreover, it dissolves precipitates of Al3+, and Cr3+ as a result of formation of AlO2-, CrO42- complexes.

  • Can Barium Nitrate [Ba(NO3)2]solution be used instead of Barium Chloride [BaCl2]for testing sulphate ions [SO42-]?

Yes, since it is the Ba2+ ions which interact with SO42- and form the white precipitate of Barium sulphate [Ba SO4].

  • Sometimes a white precipitate is obtained in Group VI even in the absence of magnesium cation [Mg2+]. How?

This happens if the fifth group cations have not been precipitated there completely.

  • In the test for bromide ion [Br], why does only organic layer acquire brown colour?

Because Br2 formed is soluble in organic solvents.

  • Ammonium molybdate test applied for phosphate ions [PO43-] on a solution is positive but it doesn’t contain phosphate ions [PO43-] . How?

If the solution contains arsenate salt of arsenic, then this happens.

  • Why does Bromide not give chromyl chloride test?

Because chromyl chloride isn’t stable.

  • What is the chemical name of the yellow precipitate formed in Ammonium molybdate test of phosphate ion [PO43-] ?

Ammonium phosphomolybdate

You can also get Class XII Practicals on BiologyPhysics, and Physical Education.

Viva Voce – Questions on Titration Practicals

  • Why is diluted sulphuric acid [H2SO4] added while preparing standard Mohr’s solution?

It is added to prevent hydrolysis of ferrous salt.

  • Can you use hydrochloric acid [HCl] or nitric acid [HNO3] in potassium permanganate [KMNO4] titrations? Why?

No. HNO3 is itself an oxidising agent whereas HCl being oxidisable to chlorine and hydrogen consumes permanganate.

  • What is the oxidation number of manganese in potassium permanganate [KMNO4] ?

Oxidation number of manganese in KMNO4 is 7.

  • Why are hot solutions not poured into graduated apparatus like durette, measuring flask etc.?

Hot solutions may expand glass and thereby introduce errors in volume measurement.

  • Why do we heat the oxalic acid to 60o– 70o C?

Heating is done to enhance the rate of reaction and increase activation energy.

  • What happens if we heat oxalic acid above 100o C?

It may decompose oxalic acid into carbon dioxide [CO2] and carbon monoxide [CO].

  • What is autocatalysis?

The reaction in which product acts as a catalyst to the reaction.

  • Should a titration flask also be rinsed?

No, rinsing of the flask will increase the volume more than pipetted one.

You can also get Class XII Practicals on BiologyPhysics, and Physical Education.

Concept of Money and Money Supply (Macroeconomics)

Nature of Money and evolution

Exchange is a way of life and money is an instrument that facilitates exchange. Hence, we can say that nature of money is one that facilitates exchange.

Before money came into being, goods were exchanged for goods. This system is known as barter system of exchange. However, barter system proved to be inefficient considering the increased wants and greater need of exchange. Therefore, money was invented as a solution to the problem of not having a common medium of exchange.

Metal coins of gold and silver were the first to come followed by alloy coins and finally the paper currency. The 21st century saw the introduction of plastic money in form of debit cards and credit cards.

Barter system and its drawbacks 

It is an exchange system in which goods are exchanged for goods. For example, I am a dairy producer who sells milk and I need a pair of shoes. I would search for a person to whom I can sell milk in return of a pair of shoes. This is also known as double coincidence of wants. This means that my want of shoes must coincide with somebody’s want of milk. As you can see in the diagram, needs of two persons should coincide or match for barter system to work.

An economy where such system of exchange works is known as a C-C economy.  A C-C or Commodity to Commodity economy is one which is influenced by Barter system of exchange. Hence you can see that Barter System, double coincidence of wants and C-C economy are all related concepts.

The Barter system had its own drawbacks as well. If you remember I asked you to think over this question earlier. As you can see in the diagram, these are the four major drawbacks. We will talk about each of these drawbacks in detail now.

Difficulty of double coincidence of wants

For double coincidence of wants to exist, wants of two individuals should coincide. This possesses a major problem as you cannot always find a suitable person who wants your shirt and at the same time has rice that you want to buy. Hence, money was invented to solve this problem.

Lack of common unit of value

Under barter system, goods are valued against goods. For example, a bike would be valued against shoes. Or rice would be valued against a cow. This makes exchange difficult. With no common unit of value, it was difficult to estimate prices of products. Money provided that common unit value and a better financial accounting system.

Lack of system for future payments

In a barter system, it is difficult to do such payments which are to be given in the future. It is also problematic when payments for any service has to be made. For example, I hire a person to repair my tap. Now, it is difficult to conclude payments in the form of goods for the service he offered.

Money solved this problem as there is an option to pay the service man at a later date and time.

Lack of system for storage and transfer of value

Since there was no money in the C-C Economy, wealth was stored and saved in the form of goods which was a problematic issue. Moreover, transfer of wealth from one individual to another also was a herculean task. Evolution of money made storage and transfer easy.

Defining Money

Money can be described something that:

  • acts as an instrument of exchange
  • is a store of value
  • is a measure of value
  • a standard for deferred payments

These are the four major components of the definition of money. Basically, money performs or has the ability to perform these functions.

We can also define money from a narrow and broad perspective. As per the narrow concept, things which act as money will be included in money. For example, all the coins, paper currency and even cheques and deposits will constitute money.

As per the broad concept, something that can be converted into money at a later date is also included in the definition of money. These include term or fixed deposits. So, both money items and future money items (which can be converted into money at later date) together constitute broad definition of money.

Moving on, now let’s talk about fiat money and fiduciary money. Money issued by the government authority is known as fiat money. Any Currency will be an example for this

On the other hand, money which is backed up by trust between payer and payee is known as fiduciary money. There is no issuing or ordering authority in this case. Cheque is an example for this. They work on the principle of trust between payer and payee.

Now let’s get a bit technical and understand the difference between money value of money and commodity value of money. Money value of money is something which is inscribed or printed on the money. For example, money value money of a 10 rupee note is 10 as that is printed over it.

Whereas commodity value of money is the intrinsic value of money or the value of material used in making the money. For example, value of steel in making a coin will be known as commodity value of money.

And finally, we will understand the difference between full bodied money and credit money. Full Bodied money is when the money value (value printed on the currency) is equal to the commodity value (value of the material of which the currency is made). On the other hand, credit money is when the money value is more than the commodity value.

Functions of Money

Functions of money can be broadly divided into four parts:

  • Primary functions
  • Secondary functions
  • Static Functions and
  • Dynamic functions

Primary Functions

1. Medium of exchange

Money acts as a medium of exchange between two individuals. For example, I can buy a good or a service by paying a certain amount for it. This allows for greater exchange of goods and services which was not the case in Barter System. Introduction of Money has also separated the acts of sale and purchase due to which the economic activities have increased.

2. Measure of Value

Earlier, value of a good was valued in terms of other good (in the barter system). Now, each good is valued in terms of money which means money serves as a measure of value. This is also known as unit of account which means that value of each good is measured in monetary terms. Exchange becomes easier considering money acts as a common denominator of value. For example, I can buy shoes or shirts by paying a certain amount.

Secondary Functions

1. Deferred Payments

Payments which are made in the future are referred to as deferred payments. Money has allowed for deferred payments to be made. Now, we can use a service or buy a product and pay for it later. One can also borrow money and pay it at a later date. This promotes economic activities at a faster pace.

2. Store of Value

Money allows storage of wealth or value conveniently which was not possible in the Barter system. This is possible because Money has the feature of general acceptability, is secure and does not require much space. This is also known as asset function of money. This also means that money can be used for investment and business purposes.

3. Transfer of Value

Transferring wealth has become easier because of money. For example, I can transfer money to another person allowing him to complete a purchase at a far-off place. This feature of money has allowed for increased economic activities considering purchasing power now can be transferred easily.

Static Functions

These include those functions which ONLY help in regulating the economy of a country. They do not aim for fostering growth and development. These include both primary and secondary functions (which we have already discussed).

Dynamic Functions

These are the functions which help in improving growth and development in the economy.  For example, any step by the government in either raising or decreasing the purchasing power will constitute as a dynamic function.

Supply of Money Concept

Supply of Money basically means the amount of money held by all the people of a country at a point of time. This is a stock concept and not a flow concept as it is concerned only with the money held for a particular period of time.

This concept does not include the government or the suppliers of money and only individuals who deal with money.

After we know what supply of mean, I think it’s important to know about the suppliers of money in the economy.

These are the three main suppliers of money who regulate the supply of money in the economy:

  • Government
  • Central Bank ( Reserve Bank of India)
  • Other commercial banks

Accordingly, these are not included while measuring supply of money.

Moving on, now we will discuss about measurement of Supply of Money. There are 4 ways of measuring it:

The first way of measuring supply of money is by combining the public currency, deposits with the bank and other deposits. As you can see in the slide, formula for M1 measurement is:


  • ‘C’ here refers to currency which the public has like coins and notes.
  • ‘DD’ refers to demand deposits with the banks.
  • ‘OD’ means other deposits which includes deposits of foreign banks, foreign governments and international financial institutions with the Reserve Bank of India

These are the formulas for m2 measurment, M3 measurment and M4 measurment

M2= M1+ Deposits of public with Post Office Saving Account

M3= M1+ Net Time Deposits (Deposits for fixed term like Fixed Deposits) with the commercial Banks

M4= M3+ Total Deposits with Post Office

M1 and M2 measure are narrower in approach whereas M3 and M4 are broader in approach while calculating the money supply.

You need to remember the M1 measurement as that is the basis for all other measurements.

You can also find Class XII Notes for for Business Studies, Accounts, Maths and Economics.

Determining resistance per cm of given wire by plotting a graph of potential difference versus current

AIM To determine the resistance per cm of a given wire by plotting a graph of potential difference versus current.

Battery, key, rheostat, voltmeter, ammeter, resistance wire (unknown resistance), connecting wires, meter scale, sandpaper.

This Experiment is based on OHM’S LAW
Ohm’s Law states that the electric current passing through a conductor is directly proportional to the potential difference applied across its ends.
Mathematically, V=IR
The resistance R of the wire depends on the material of the wire and its dimensions.


internal resistance
Circuit Diagram – Determining Unknown Resistance


  1. Draw the circuit diagram as shown in figure above
  2. Arrange the apparatus as per the circuit diagram
  3. Clean the ends of the connecting wires with sandpaper and make them shiny.
  4. Make the connections as per circuit diagram. All connections must be neat and tight. Take care to connect the ammeter and voltmeter with their correct polarity. (+ve to +ve and -ve to -ve)
  5. Determine the zero error and least count of the ammeter and voltmeter and record them.
  6. Adjust the rheostat to pass a low current.
  7. Insert the key K and slide the rheostat contact to see whether the ammeter and voltmeter are showing deflections properly.
  8. Adjust the rheostat to get a small deflection in ammeter and voltmeter.
  9. Record the readings of the ammeter and voltmeter
  10. Take at least six sets of readings by adjusting the rheostat gradually
  11. Plot a graph with V along X axis and I along axis.
  12. The graph will be a straight line which verifies Ohm’s law
  13. Determine the slope of the V-I graph. The reciprocal of the slope gives the resistance of the wire.


  1. Range
    Range of the given Ammeter =  0-500m A
    Range of the given voltmeter =  0-5V
  2. Least Count
    Least Count of the given Ammeter = 10mA
    Least Count of the given voltmeter = 0.1V
  3. Zero Error
    Zero Error of the given Ammeter = 0A
    Zero Error of the given voltmeter = 0V
  4. Zero Correction
    Zero Correction of the given Ammeter = 0A
    Zero Correction of the given voltmeter = 0V
  5. Observation Table for Ammeter and Voltmeter Readings
S No Ammeter Observed (A) Ammeter Corrected (A) Voltmeter Observed (V) Voltmeter Corrected (V) Ratio (V/I) = R (ohm)
1 0.3 0.3 0.1 0.1 0.33
2 0.7 0.7 0.2 0.2 0.28
3 1.1 1.1 0.3 0.3 0.27
4 1.5 1.5 0.4 0.4 0.26
5 1.9 1.9 0.5 0.5 0.26


Voltage v/s Current Graph
Voltage v/s Current Graph

Mean Value of V/I from observations, R = 0.28Ω
Length of resistance wire = 40.2cm
Value of slope of VI graph =0.27 Ω
Resistance per unit length = 0.675 Ωm-1


  1. Ohm’s Law is verified as the I vs V graph is a straight line
  2. The resistance of the given wire = 0.28Ω
  3. The resistance per cm of given wire is 0.675 Ω m-1.


  1. All the electrical connections must be neat and tight.
  2. Voltmeter and Ammeter must of proper range
  3. The key should be inserted only while taking readings.


  • Give the mathematical form of Ohm’s law.
    V = RI,  is the mathematical representation of Ohm’s law.
  • State Ohm’s Law
    Ohm’s law states that the electric current ‘I’ flowing through a conductor is directly proportional to the potential difference V (voltage) across its ends (provided that the physical conditions, temperature, pressure, and dimensions of the conductor remain same).
  • What is the material chosen for rheostat wire and why?
    It is constantan alloy. It is chosen to make rheostat as its resistivity is very high and temperature coefficient of resistance is quite small.
  • What is the material used for making connection wires?
    Here, copper has been used.
  • What are the factors affecting resistance?
    The resistance depends upon length, the area of cross-section, nature of material and temperature of conductors.
  • What is electrical current? Define its S.I. unit?
    The flow of electric charge per unit time through a conductor is called the electric current. It’s S.I. unit is ampere (A). 1 Ampere is the amount of current flowing in a conductor which offers resistance 1 Ohm when 1 V potential difference is maintained across the conductor.
  • Define S.I. Unit of electric potential.
    S.I. unit of electric potential is Volt. 1 Volt is said to be the potential difference between two points if 1 joule of work is done in bringing 1 coulomb of charge from one point to the other.
  • Why is ammeter connected in series?
    To measure the current without any change in magnitude.
  • Why is voltmeter connected in parallel?
    A voltmeter is connected in parallel so that it can measure the potential drop without any change in its magnitude.

You can also get Class XII Practicals on BiologyPhysics, and Physical Education.