Two cells of emf $E_1$ and $E_2$ and internal resistances $r_1$ and $r_2$ respectively are connected in parallel. The equivalent emf and internal resistance of the combination will be:

E.C.E. of $Cu$ and $Ag$ are $7 imes {10^{ - 6}}$ and $1.2\,\, imes \,{10^{ - 6}}$. A certain current deposits $14\,\,gm$ of $Cu$. Amount of $Ag$ deposited is

A cell of ${\rm{e}}{\rm{.m}}{\rm{.f}}{\rm{.}}\,\,E$ connected with an external resistance $R$, then p.d. across cell is $V$. The internal resistance of cell will be

A battery of $emf$ ${\rm{E}}$ produces currents ${I_1}$ and ${I_2}$ when connected to external resistances ${R_1}$ and ${R_2}$ respectively. The internal resistance of the battery is

A direct current of 4A and an alternating current of 4A flows through two identical resistors. The ratio of heat produced in the two resistances in same time interval will be

Which of the following is the basic structural and functional unit of life?

It is possible that any some constant value of emf, but the potential difference between the plates is zero?

A current of two ampere is flowing through a cell of ${\rm{e}}{\rm{.m}}{\rm{.f}}{\rm{.}}\,\,5\,\,volt$ and internal resistance $0.5\,\,ohm$ from negative to positive electrode. If the potential of negative electrode is $10\,\,V$, the potential of positive electrode will be

When a resistance of $2\,\,ohm$ is connected across the terminals of a cell, the current is $0.5\,\,ampere$. When the resistance is increased to $5\,\,ohm$, the current is $0.25\,\,ampere$. The internal resistance of the cell is

A voltmeter having a resistance of $998\,\,ohm$ is connected to a cell of e.m.f. $2\,\,volt$ and internal resistance $2\,\,ohm$. The error in the measurement of e.m.f. will be

Twelve cells, each having emf ${\rm{E}}$ volts are connected in series and kept in a closed box. Some of these cells are wrongly connected with positive and negative terminals reversed. This ${\rm{12}}\,{\rm{ - }}\,{\rm{cell}}$ battery is connected with an ammeter, an external resistance R ohm and a two-cell battery (two cells of the same type used earlier, connected perfectly in series). The current in the circuit when the ${\rm{12}}\,{\rm{ - }}\,{\rm{cell}}$ battery and ${\rm{2}}\,{\rm{ - }}\,{\rm{cell}}$ battery aid each other is ${\rm{3}}\,{\rm{A}}$ and ${\rm{2}}\,{\rm{A}}$ when they oppose each other. Then, the number of cell in ${\rm{12}}\,{\rm{ - }}\,{\rm{cell}}$ battery that are connected wrongly is