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Q.1
Based on: WBCS Prelims 2004
Which type of electrochemical cell stores chemical energy but converts it irreversibly during discharge?
A.Primary cell
B.Secondary cell
C.Fuel cell
D.Electrolytic cell
Explanation
Why Correct: Primary cells (non-rechargeable batteries) store chemical energy that is converted to electrical energy through irreversible chemical reactions during discharge. Once discharged, they cannot be recharged by electrical means. Distractor Analysis: Secondary cells (rechargeable batteries) store chemical energy reversibly. Fuel cells continuously convert chemical energy from external fuel sources. Electrolytic cells use electrical energy to drive non-spontaneous chemical reactions. Takeaway: Primary cells like alkaline batteries and zinc-carbon batteries operate through irreversible electrochemical reactions, making them single-use devices.
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Q.2
Based on: WBCS Prelims 2004
What fundamental property of matter is quantified by the SI unit coulomb?
A.Electric potential
B.Chemical energy
C.Electric charge
D.Electromotive force
Explanation
Why Correct: Electric charge is the intrinsic property of matter responsible for electromagnetic interactions. The coulomb measures the quantity of electric charge. Distractor Analysis: Electric potential is the work done per unit charge, measured in volts. Chemical energy is stored in molecular bonds and converts to other forms in batteries. Electromotive force is the maximum potential difference of a source when no current flows. Takeaway: The elementary charge carried by a proton or electron is approximately 1.6 × 10^-19 coulombs.
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Q.3
Based on: WBCS Prelims 2004
The work done per unit positive charge in moving it from infinity to a point in an electric field defines which quantity?
A.Electric current
B.Electric potential
C.Chemical energy
D.Electric charge
Explanation
Why Correct: Electric potential at a point is defined as the work done per unit positive charge in bringing it from infinity to that point against the electric field. Distractor Analysis: Electric current is the rate of flow of electric charge through a conductor. Chemical energy is stored in substances and released in reactions. Electric charge is the fundamental property measured in coulombs.
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Q.4
Based on: WBCS Prelims 2004
In a storage cell, what triggers the flow of electrons through an external circuit?
A.Chemical reactions at the electrodes
B.Electric charge accumulation
C.Electric potential difference
D.Lead or other metal oxidation
Explanation
Why Correct: Chemical reactions at the electrodes (oxidation at anode, reduction at cathode) create an electromotive force that drives electron flow through the external circuit. Distractor Analysis: Electric charge accumulation is a result of the chemical reactions, not the trigger. Electric potential difference (voltage) is the energy per charge that enables current flow but is caused by the chemical reactions. Lead or other metal oxidation occurs specifically in certain battery types but is not the universal trigger for all storage cells. Takeaway: All electrochemical cells, including both primary and secondary cells, rely on spontaneous redox reactions to generate electrical current.
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Q.5
Based on: WBCS Prelims 2004
Who invented the Daniell cell, the first practical primary cell that provided steady current?
A.Alessandro Volta
B.John Frederic Daniell
C.Gaston Planté
D.Georg Ohm
Explanation
Why Correct: John Frederic Daniell invented the Daniell cell in 1836. This primary cell used copper and zinc electrodes with copper sulfate and zinc sulfate electrolytes. Distractor Analysis: Alessandro Volta invented the voltaic pile, the first electrochemical battery. Gaston Planté invented the lead-acid battery, the first rechargeable battery. Georg Ohm formulated Ohm's law relating current, voltage, and resistance. Takeaway: The Daniell cell's design prevented polarization, allowing it to maintain steady current for extended periods unlike earlier voltaic cells.
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