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Types of cells - class-VII

Description: types of cells
Number of Questions: 39
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Tags: physics electricity
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Three types of electric cells which provide current are:

  1. Button cell, solar cell & secondary ceil

  2. Solar cell, electrolytic cell, electro chemical cell

  3. (A) and (B) both are correct

  4. Neither (A) nor (B) is correct


Correct Option: C
Explanation:

Answer is C.

When a primary cell is used, chemical reactions in the battery use up the chemicals that generate the power; when they are gone, the battery stops producing electricity and is useless. In contrast, in a secondary cell, the reaction can be reversed by running a current into the cell with a battery charger to recharge it, regenerating the chemical reactants. 
The types of cells mentioned in option A and option are correct.
Hence, option C is correct.

Which one of the following solutions can be electrolysed ?

  1. Mercury

  2. Distilled water

  3. Solution of common salt

  4. Milk


Correct Option: C
Explanation:

When dissolved in fluid, salts tend to break apart into their component ions, creating an electrically-conductive solution. Common salt is one such salt. common salt is  $ NaCl$ which gives $Na^+$ and $Cl^-$.

Which one of the following primary cells has e.m.f. $1.08  V$ and which remains fairly constant ?

  1. Daniel cell

  2. Simple voltaic cell

  3. Leclanche cell

  4. Dry cell


Correct Option: A
Explanation:

the Daniel cell is a type of electrochemical cell invented in 1836. it is consisted of a copper pot filled with a copper sulfate solution , in which was immersed an unglazed earthenware container filled with sulfuric acid and a zinc electrode. Daniel cell is also called Zn-Cu cell and has constant e.m.f of 1.08 volts.

To remove the polarisation defect in Daniel cell ?

  1. Zinc rod is coated with a thin layer of mercury

  2. Potassium bi-chromate is used

  3. The cell should be kept in open air

  4. Copper-sulphate is used


Correct Option: D
Explanation:

A depolarizer in electrochemistry is a synonym of electroactive substance, i.e., a substance which changes its oxidation state, or partakes in a formation or breaking of chemical bonds, in a charge-transfer step of an electrochemical reaction. In the cells, the term "depolarizer" has been used to denote a substance used in a primary cell to prevent buildup of hydrogen gas bubbles.

The hydrogen ions displace metal from the salt so that metal, instead of hydrogen, is deposited on the positive plate. For example, copper-sulphate in Daniel cell.

In a cell, by convention, electron is taken to be flowing from

  1. positive electrode to negative electrode.

  2. negative electrode to positive electrode.

  3. both A and B

  4. none of the above.


Correct Option: B
Explanation:

By convention, current is assumed to travel from positive to negative direction. The electrons travel from negative to positive. The direction of current is not the same as direction of flow of electrons; they are opposite.

Which among the following is a standard cell ?

  1. Daniel cell

  2. Cadmium cell

  3. Leclanche cell

  4. Lead accumulator


Correct Option: B
Explanation:

The ideal qualities of standard cells as follows:
(1) The cells must be constructed from high purity materials and be reproducible.
(2) Except when current is flowing there should be no chemical reaction taking place in the cell.
(3) When the cell is thermally cycled it must give the same emf at a given temperature regardless of its thermal history.
(4) When a current is passed through the cell, its emf may change, but it must recover rapdidly and completely on cessation of the current.

(1) to (4) above represent an ideal qualities which only the Weston Standard cell approaches. The Weston Standard cell is constructed with the basic materials- mercury, cadmium, sulfuric acid, and water- are all purified by distillation, starting with the purest materials available. Hence out of given cells cadmium cell is the standard cell.

In daily life, dry cell is used in 

  1. Fan

  2. Alarm clock

  3. Tubelight

  4. All out(Mosquito repellant)


Correct Option: B
Explanation:

Alarm clock uses Dry Cell. Rest of the components work on power supply.

When the ends of metal wire are not connected to a battery

  1. electrons move from positive electrode to negative electrode.

  2. electrons move from negative electrode to positive electrode.

  3. electrons move in random directions.

  4. protons move in random direction in such a way that their net movement in a unit volume is zero.


Correct Option: C
Explanation:

When the ends of the metal wire are not connected to a battery, no electric field is produced inside the wire. Thus no force acts on the electrons in the wire. So the electrons collide with each other and move in random directions.

Nickel Cadmium cells are used in

  1. very long-life applications

  2. devices with high limitation on spaces.

  3. portable machines that run on electricity.

  4. all of the above


Correct Option: C
Explanation:

Nickel cadmium cells are used in portable machines that run on electricity. It is rechargeable.

Button cell is also called as

  1. lithium cell.

  2. nickel-cadmium cell

  3. dry cell

  4. leclanche cell


Correct Option: A
Explanation:

Lithium cell has a negative plate of lithium iron phosphate and a positive plate of carbon. It is also called as button cell.

When an electron moves from negative electrode to positive electrode

  1. negative charge moves from negative electrode to positive electrode.

  2. positive charge moves from positive electrode to negative electrode.

  3. no charge flows from either electrode to other electrode.

  4. both A and B


Correct Option: D
Explanation:

Electrons are termed as negative charged particles. Thus when electrons move from negative electrode to positive electrode, we say that negative particles move from negative electrode to positive electrode. On the other hand, the positive charges get attracted towards the negative electrode, thus they move from positive electrode to negative electrode.

Which one works with the help of dry cell?

  1. Torches

  2. Transistors, toys

  3. T.V.remotes

  4. All of these


Correct Option: D

Out of the following the one which is a source of e.m.f is:

  1. voltaic cell

  2. dynamo

  3. thermocouple

  4. lous speaker


Correct Option: A
Explanation:

A voltaic cell is an electrochemical cell that produces electrical energy. In voltaic cell there is an anode where oxidation occurs and a cathode where reduction occurs. So, it produces current and thus emf is produced in voltaic cells.

For a cell reaction involing a two-electron change, the standard e.m.f of the cell is fonud to be$0.295V$ at $25^{o}C$. The equilibrium constant of the reaction at $25^{o}C$ will be:

  1. $10$

  2. $1\ \times 10^{10}$

  3. $1\ \times 10^{-10}$

  4. $29.5\ \times 10^{-2}$


Correct Option: D

The electric cell is a device to obtain ?

  1. electric charge

  2. electric force

  3. electrons

  4. electric energy from chemical energy


Correct Option: D
Explanation:

It is a common misconception that battery or cell delivers charge but this is not true at all.The battery as a whole is electrically neutral and its only job is to provide electrical energy.This is usually done using conversion of chemical energy to electric energy.

An electrochemical cell stops working after some time because

  1. Electrode potential of both the electrodes become zero.

  2. Electrode potential of both the electrodes become equal.

  3. One of the electrode is eaten away.

  4. The reaction starts proceeding in opposite direction.


Correct Option: A

A $100$ watt, $110$ volt lamp is connected in series with an electrolytic cell containing $CaSO _4$ solution, the weight of Cd deposited by the current for $10$ hrs is (Sl.wt. of Cd=112.4)

  1. $19.06$g

  2. $38.12$g

  3. $1.906$g

  4. $3.812$g


Correct Option: B

In an electric containing battery, the positive charge inside the battery.

  1. always goes from the positive terminal to the negative terminal

  2. may go from the positive terminal to the negative terminal

  3. always goes from the negative terminal to the positive terminal

  4. May go either side depending on the absolute value of the electric field.


Correct Option: D

The power supplied by a battery (or source) is maximum when the external resistance 'R' is equal to the 

  1. Internal resistance 'r'

  2. Half of the internal resistance 'r'

  3. Two times of initial resistance 'r'

  4. None of these


Correct Option: A

A cell of emf E is connected across a resistance r . The potential difference terminals of the cell is found to be V . The internal resistance of the cell must be 

  1. $\dfrac { \left( E-V \right) V }{ r } $

  2. $\dfrac { 2\left( E-V \right) V }{ r } $

  3. $\dfrac { \left( E-V \right) r }{ V } $

  4. $\left( E-V \right) r$


Correct Option: C

A cell drives a current of 1 A in to load of resistance $4W$. On doubling the load resistance. the current is found to be reduced by $40 \%$. The internal resistance of the cell is

  1. $0.5 W$

  2. $1 W$

  3. $4 W$

  4. $2 W$


Correct Option: A

The Zinc rod in leclanche cell is coated with a thin layer of mercury because

  1. The defect of polarization is removed.

  2. The defect of local action is removed.

  3. The cell does not remain dirty.

  4. The cell is brightened.


Correct Option: B
Explanation:

Local Action is the tendency for the chemically active components of a cell to react with each other, and so become exhausted even when no current is being drawn from the cell. Local action has the effect of reducing the 'shelf-life' of the cell - it uses up its chemical reserves and becomes exhausted even when not being used.

In a cell formed from zinc and copper electrodes suspended in a weak acid solution, local action can be seen. The zinc becomes coated with hydrogen bubbles, as a result of its reacting with the acid, even when no current is being drawn. After a while either the zinc will be entirely consumed, or the acid will be neutralised. To avoid this, a thin layer of mercury is coated on zinc rod.

Primary cell are connected in parallel to

  1. Increase voltage

  2. Decrease capacity

  3. Decrease internal resistance

  4. Make electric current constant


Correct Option: C
Explanation:

Equivalent resistance of parallel combination         $\dfrac{1}{R _{eq}}  = \dfrac{1}{R _1}+\dfrac{1}{R _2} + .......$


$\implies$ Equivalent resistance of the parallel combination is less than the minimum of the individual resistance used.

Hence primary cell are connected in parallel to decrease the internal resistance.

What is the e.m.f. of a dry cell ?

  1.  $1.5 V$

  2. $2.5 V$

  3.  $1.1 V$

  4. $-1.1 V$


Correct Option: A
Explanation:
A common dry cell is the zinc–carbon battery, sometimes called the dry Leclanché cell, with a nominal voltage of 1.5 volts, the same as the alkaline battery (since both use the same zinc–manganese dioxide combination).Hence the correct option A.

The depolariser used in Laclanche cell is

  1. Solution of ammonium chloride

  2. Porous pot

  3. Powdered carbon

  4. Manganese dioxide


Correct Option: D
Explanation:

A battery depolarizer takes up electrons during discharge of the cell and thus it is always an oxidizing agent. The term depolarizer has been used to denote a substance used in primary cell to prevent build up of hydrogen gas bubbles. Manganese dioxide is used as depolarizer in Leclanche cell and dry cell.

When the two terminals of a battery are connected directly with a wire then:

  1. more electrical energy is stored in the cell

  2. the chemical energy stored get used up very fast.

  3. no current flows in the wirc

  4. none of these.


Correct Option: B
Explanation:

Battery is the source of potential difference and wire is a conductor but can't be a perfect conductor. It has some resistance in which voltage gets dropped. As resistance of wire is much smaller so it will be large amount of current through battery and battery will get discharged much sooner.the chemical energy stored get used up very fast.

Electro chemical equivalent of substance is 0.0006735 ; its eq. wt. is :

  1. 65

  2. 67.35

  3. 130

  4. cannot be calculated


Correct Option: A

In a cell, electrons move from

  1. positive electrode to negative electrode.

  2. negative electrode to positive electrode.

  3. both A and B

  4. electrons do not move and only negative charge moves from one place to another place.


Correct Option: B
Explanation:

We know that the current flows from positive electrode to negative electrode in a cell. The direction of electrons is always opposite to the direction of the current. Thus, the electrons move from negative electrode to positive electrode.  

Which one of the following statement is not true for Daniel cell ?

  1. The e.m.f. of this cell changes rapidly

  2. Some crystals of copper sulphate are added in it to make the solution saturated

  3. This cell was made first of all in 1850 by the scientist Daniel

  4. The hollow cylinder or the vessel of copper acts as the positive plate


Correct Option: A
Explanation:

The e.m.f of a Daniel cell always remains constant and is equal to $1.08$ volts.

And  all the other statements given are true.

Direction of electric current inside the cell is from

  1. positive electrode to negative electrode.

  2. negative electrode to positive electrode.

  3. positive electrode to positive electrode.

  4. negative electrode to negative electrode.


Correct Option: B
Explanation:

When an external circuit is connected across the cell, electrons flow from negative electrode to positive electrode(current flows opposite to this) in the external circuit. Inside the cell, negatively charged ions are attracted to negative electrode because it is depleted of electrons. Similarly, inside the cell, positively charged ions are attracted to positive electrode. 

Hence inside the cell, current flows from negative electrode to positive electrode.

The common dry cell produces a voltage of

  1. $1.5 V$

  2. $4 V$

  3. $2 V$

  4. $3 V$


Correct Option: A
Explanation:

A common dry cell is zinc-carbon cell with a normal voltage of 1.5 V , same as the alkaline cell.

A battery converts chemical energy into

  1. mechanical energy

  2. solar energy

  3. electrical energy

  4. none of these


Correct Option: C
Explanation:

A battery converts chemical energy into electrical energy.


Answer-(C)

Which of the following is not the storage cell?

  1. Acid cell

  2. NIFE cell

  3. Edison cell

  4. Dry cell


Correct Option: D
Explanation:

Dry cell being primary cell, cannot be recharged.
Acids cell are used as car batteries.
The nickel-iron battery (Ni-Fe battery)( also called Edison Cell)  is a rechargable battery having nickel(III) oxide-hydroxide positive plates and iron negative plates, with an electrolyte of potassium hydroxide. It is a very robust battery which is tolerant of abuse, (overcharge, overdischarge, and short-circuiting) and can have very long life even if so treated.

First electro chemical cell was designed by?

  1. Laclanche

  2. Faraday

  3. Galvanic

  4. Some one other than those mentioned above


Correct Option: D
Explanation:

The battery made by Volta is credited as the first electrochemical cell. It consists of two electrodes: one made of zinc, the other of copper. The electrolyte is either sulfuric acid mixed with water or a form of saltwater brine.

In which of the following cells polarisation is the major defect?

  1. Voltaic cell

  2. Daniel cell

  3. Leclanche cell

  4. Fuse cell


Correct Option: A
Explanation:

The chemical action that occurs in the cell while the current is flowing causes hydrogen bubbles to form on the surface of the anode. This action is called POLARIZATION. Some hydrogen bubbles rise to the surface of the electrolyte and escape into the air, some remain on the surface of the anode. If enough bubbles remain around the anode, the bubbles form a barrier that increases internal resistance. When the internal resistance of the cell increases, the output current is decreased and the voltage of the cell also decreases.

Voltaic cell has a lot of polarization due to ongoing reactions.Daniell cell is 
an improvement on the voltaic cell using two electrolytes and solves the problem of polarisation.

Which of the following effect of electric current is used in charging a battery of motor car?

  1. Magnetic

  2. Heating

  3. Chemical

  4. Induction


Correct Option: C
Explanation:

The charging of all secondary batteries are based on conversion of electric energy to chemical potential energy with the user of battery charger. The negative terminal of the cell has to be connected to the negative terminal of the voltage source and the positive terminal of the voltage source with the positive terminal of the battery. Further, the voltage output of the source must be higher than that of the battery, but not much higher: the greater the difference between the power source and the battery's voltage capacity, the faster the charging process, but also the greater the risk of overcharging and damaging the battery.

A cell constructed by coupling a standard copper electrode and a standard magnesium electrode has emf of $2.7$ volts. If the standard reduction potential of copper electrode of $+0.34\ V$, that of magnesium electrode is

  1. $+3.04\ V$

  2. $-3.04\ V$

  3. $+2.36\ V$

  4. $-2.36\ V$


Correct Option: D
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