In the given circuit the current $I_1$ is .............. $A$
A$0.4$
B$-0.4$
C$0.8$
D$-0.8$
Diffcult
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B$-0.4$
b (b) The circuit can be simplified as follows
Applying $KCL$ at junction $A$
${i_3} = {i_1} + {i_2}$.….$(i)$
Applying Kirchoff’s voltage law for the loop $ABCDA$
$ - 30{i_1} - 40{i_3} + 40 = 0$
$ \Rightarrow \,\,\,\,\,\, - 30{i_1} - 40({i_1} + {i_2}) + 40 = 0$
$ \Rightarrow \,\,\,\,\,\,\,7{i_1} + 4{i_2} = 4$ .….$(ii)$
Applying Kirchoff’s voltage law for the loop $ADEFA.$
$ - 40{i_2} - 40{i_3} + 80 + 40 = 0$
$ \Rightarrow \,\,\,\,\, - 40{i_2} - 40({i_1} + {i_2}) = - 120$
$ \Rightarrow \,\,\,\,\,\,{i_1} + 2{i_2} = 3\,$…….$(iii)$
On solving equation $(ii)$ and $(iii)$ ${i_1} = - 0.4\,A$.
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A current of $5\; {A}$ is passing through a non-linear magnesium wire of cross-section $0.04\; {m}^{2}$. At every point the direction of current density is at an angle of $60^{\circ}$ with the unit vector of area of cross-section. The magnitude of electric field at every point of the conductor is ....${V} / {m}$ (Resistivity of magnesium is $\rho=44 \times 10^{-8}\, \Omega m$)
Two resistance of $100\ \Omega$ and $200\ \Omega$ are connected in series with a battery of $4 \mathrm{~V}$ and negligible internal resistance. $A$ voltmeter is used to measure voltage across $100 \Omega$ resistance, which gives reading as $1 \mathrm{~V}$. The resistance of voltmeter must be ___$\Omega$.
.............. $A$ the current flowing through the resistance $R_2$ of the circuit shown in fig if the resistance are equal to $R_1 = 20\ \Omega, R_2 = 30 \ \Omega$ and $R_3 = 60 \ \Omega$ and potentials of points $1, 2$ and $3$ are equal to $V_1= 20\, V,$ $V_2 = 30\ V$ and $V_3 = 60\ V$