List of top Physics Questions on Current electricity asked in UP Board XII

Option 1: Depict the series and the parallel combination of cells. When is the series and when is the parallel combination suitable? A cell of e.m.f. \( E \) and internal resistance \( r \) is connected with an external resistance \( R \). Draw a graph between the voltage \( V \) across \( R \) and the current \( i \) flowing in it.
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Option 2: State Ampere's circuital law and, on its basis, find the formula for the magnetic field produced at a point due to an infinitely long straight current-carrying wire. A current of \( 10^{-4}\ \text{A} \) flows in a rectangular coil of dimensions \( 1.0\ \text{cm} \times 1.5\ \text{cm} \). The plane of the coil is parallel to a magnetic field of \( 0.6\ \text{N/A m} \). The coil has 30 turns. Calculate the torque acting on the coil.
Define current density \( (\vec{J}) \) and write its unit. Prove that \( \vec{J} = \sigma\vec{E} \), where \( \sigma \) is the specific conductivity (conductivity) of the conductor and \( \vec{E} \) the electric field inside the conductor.
Two resistances are connected in parallel. Equivalent resistance of combination is \(\tfrac{6}{5}\ \Omega\). When one resistance is broken out, resistance becomes \(2\ \Omega\). The resistance of broken wire was:

Obtain the formula for the current flowing in the resistor R, with the help of the circuit given above. (Two cells of e.m.f. \( E_1 \) and \( E_2 \) with internal resistances \( r_1 \) and \( r_2 \) are connected in parallel and feed a common external resistor R.)
What will be the effect on the drift velocity of electrons, when the current in a copper wire is passed in a wire, twice of its radius (the same current being maintained)?
Equivalent resistance \( R \) is obtained when \( n \) wires having the same length and same thickness of the same material are joined in parallel. The equivalent resistance on joining them in series will be:
Define and write the formula of mobility.
What is relaxation time? Find the equation of the relation between drift velocity and relaxation time.

Find the current supplied by the battery in the network shown in the figure. Also calculate the terminal voltage across the cell and the charge on the capacitor.
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What do you mean by electromotive force (EMF) of a cell? In the circuit shown, calculate the terminal voltage of the cell C. The battery B is of negligible internal resistance.
Two resistors \(R\) and \(2R\) are connected in parallel in an electric circuit. The thermal energies developed in \(R\) and \(2R\) are in the ratio:
Resistance of a wire is 16 ohm. By melting it, its length is stretched to half of its original length. What will be the resistance of the new wire?
Write Ohm's law. Deduce Ohm's law on the basis of drift velocity of electron.
Write the definition of specific conductivity and its unit.
Resistance of a wire is \( R \). If the length of the wire is stretched by \( n \) times the original length, then what will be the new resistance of the wire?
What do you understand by free electron and drift velocity? Deduce Ohm's law on the basis of the principle of drift velocity.
Write the definitions of electrical conductivity and specific conductivity.
Potential difference at the ends of a conductor of length \(l\) is \(V\). Diameter of the conductor is \(d\). What will be the effect on the electric field inside the conductor and its resistance, if (i) \(V\) is halved? (ii) \(l\) is doubled? (iii) \(d\) is doubled?
Explain Kirchhoff's laws related to electrical circuits.
Resistances of \( 10\ \Omega \) and \( 15\ \Omega \) are connected in parallel. The combination is connected with a battery of \( V \) volt. Choose the correct statement.