A cell of $emf$ $E$ and internal resistance $r$ is connected in series with an external resistacne $nr.$ Then, the ratio of the terminal potential difference to $emf$ is
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In an aluminium $(A1)$ bar of square cross section, a square hole is drilled and is filled with iron ( $Fe$ ) as shown in the figure. The electrical resistivities of $A 1$ and $Fe$ are $2.7 \times 10^{-8} \ \Omega m$ and $1.0 \times 10^{-7} \ \Omega m$, respectively. The electrical resistance between the two faces $P$ and $Q$ of the composite bar is
A potentiometer wire of length $1\,m$ and resistance $10\,\Omega$ is connected in series with a cell of $emf$ $2\,V$ with internal resistance $1 \,\Omega$ and a resistance box including a resistance $R$. If potential difference between the ends of the wire is $1\, mV$, the value of $R$ is ............. $\Omega $
The resistance of the meter bridge $AB$ in given figure is $4\,\Omega $. With a cell of emf $\varepsilon \, = 0.5\,\,V$ and rheostat resistance $R_h = 2\,\Omega $ the null point is obtained at some point $J.$ When the cell is replaced by another one of emf $\varepsilon \, = {\varepsilon _2}$ the same null point $J$ is found for $R_h = 6\,\Omega .$ The $emf$ ${\varepsilon _2}$ is ................. $V$
The current $i_1$ and $i_2$ through the resistors $R_1(=10\,\Omega )$ and ${R_2}\left( { = 30\,\Omega } \right)$ in the circuit diagram with $E_1 = 3\,V$, $E_2 = 3\,V$ and $E_3 = 2\,V$ are respectively
In a meter bridge, as shown in the figure, it is given that resistance $Y=12.5\, \Omega $ and that the balance is obtained at a distance $39.5\, cm$ from end $A$ (by jockey $J$) . After interchanging the resistances $X$ and $Y$, a new balance point is found at a distance $l_2$ from end $A$. What are the values of $X$and $l_2$ ?
In a region $10^{19}$ $\alpha -$ particels and $10^{19}$ protons per second move to the left, while $10^{19}$ electrons moves to the right per second. The current is