A potential divider is used to give outputs of $4\,V$ and $8\,V$ from a $12\,V$ source. Which combination of resistances, $(R_1 : R_2 : R_3)$ gives the correct voltages
A$2 : 1 : 2$
B$1 : 1 : 1$
C$2 : 2 : 1$
D$1 : 1 : 2$
Medium
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B$1 : 1 : 1$
b
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A current of $1.6\, A$ is flowing through a wire having cross-sectional area $1\, mm^2$. If density of free electrons in the material of the wire is $10^{29}\, per\, m^3$, the drift velocity of electrons will be
The charge flowing in a conductor varies with time as $Q = at -bt^2$. Then for current, which statement is incorrect.
$(A)$ decreases linearly with time
$(B)$ reaches a maximum and then decreases
$(C)$ fall to zero after time $t = a/2b$
$(D)$ changes at a rate $-2b$
Options :
A primary cell has an $e.m.f.$ of $1.5\,volts$, when short-circuited it gives a current of $3$ amperes. The internal resistance of the cell is .............. $ohm$
In the circuit shown below, the switch $S$ is connected to position $P$ for a long time so that the charge on the capacitor becomes $q _1 \mu C$. Then $S$ is switched to position $Q$. After a long time, the charge on the capacitor is $q _2 \mu C$.
A cylindrical resistance is connected across battery $\varepsilon $ . Cylinder has uniform free electron density, mid part of cylinder has larger radius as shown in figure. Then $V_d$ (drift velocity) $V/S$ (distance across the length of the resistance)