List of top Physics Questions on Current electricity asked in CBSE CLASS XII

A student sets up the circuit as shown in the figure to find the value of unknown resistance X and records a set of readings of the voltmeter and the ammeter by using the rheostat.

Two wires of the same material and the same radius have their lengths in the ratio 2:3. They are connected in parallel to a battery which supplies a current of 15 A. Find the current through the wires.
In the circuit, three ideal cells of e.m.f. \( V \), \( V \), and \( 2V \) are connected to a resistor of resistance \( R \), a capacitor of capacitance \( C \), and another resistor of resistance \( 2R \) as shown in the figure. In the steady state, find (i) the potential difference between P and Q, (ii) the potential difference across capacitor C.
potential difference across capacitor C
The ratio of potential difference across AB in the circuit shown for the case (i) when switch S is closed and (ii) when S is open is:
The ratio of potential difference across AB in the circuit
\( n \) identical cells, each of e.m.f \( E \) and internal resistance \( r \), are connected in series. Later on, it was found that two cells ‘X’ and ‘Y’ are connected in reverse polarities. Calculate the potential difference across the cell ‘X’.
In the given figure, three identical bulbs P, Q, and S are connected to a battery.
three identical bulbs P, Q, and S

[(i)] Compare the brightness of bulbs P and Q with that of bulb S when key K is closed.

[(ii)] Compare the brightness of the bulbs S and Q when the key K is opened.
Justify your answer in both cases.
Two cells of emf 10 V each, two resistors of 20 \( \Omega \) and 10 \( \Omega \), and a bulb B of 10 \( \Omega \) resistance are connected together as shown in the figure. Find the current that flows through the bulb.
Two cells of emf 10 V each, two resistors
Two conductors A and B of the same material have their lengths in the ratio 1:2 and radii in the ratio 2:3. If they are connected in parallel across a battery, the ratio \( \frac{v_A}{v_B} \) of the drift velocities of electrons in them will be:
Calculate the value of the current passing through the battery in the given circuit diagram.
A conductor of length \( l \) is connected across an ideal cell of emf E. Keeping the cell connected, the length of the conductor is increased to \( 2l \) by gradually stretching it. If R and \( R' \) are initial and final values of resistance and \( v_d \) and \( v_d' \) are initial and final values of drift velocity, find the relation between:
\( R' \) and \( R \)
\( R' = 4R \)
Two wires made of the same material have the same length \( l \) but different cross-sectional areas \( A_1 \) and \( A_2 \). They are connected together with a cell of voltage \( V \). Find the ratio of the drift velocities of free electrons in the two wires when they are joined in: (i) series, and (ii) parallel.

A battery of emf \( E \) and internal resistance \( r \) is connected to a rheostat. When a current of 2A is drawn from the battery, the potential difference across the rheostat is 5V. The potential difference becomes 4V when a current of 4A is drawn from the battery. Calculate the value of \( E \) and \( r \).

A steady current \( I \) is passed through a conductor at room temperature for time \( t \). It is observed that its temperature rises by \( 0.5^\circ\text{C} \). If \( 2I \) current is passed through the conductor (at room temperature) for the same duration, the rise in its temperature will be approximately:
A conductor of length \( l \) is connected across an ideal cell of emf \( E \). Keeping the cell connected, the length of the conductor is increased to \( 2l \) by gradually stretching it. If \( R \) and \( R' \) are the initial and final values of resistance, and \( v_d \) and \( v'_d \) are the initial and final values of drift velocity, find the relation between (i) \( R' \) and \( R \) and (ii) \( v'_d \) and \( v_d \).
If \( R_s \) and \( R_p \) are the equivalent resistances of \( n \) resistors, each of value \( R \), in series and parallel combinations respectively, then the value of \( (R_s - R_p) \) is:
Two wires P and Q are made of the same material. Wire Q has twice the diameter and half the length of wire P. If the resistance of wire P is \( R \), the resistance of wire Q will be:
The figure shows the voltage (V) versus the current (I) graphs for a wire at two temperatures \( T_1 \) and \( T_2 \). One can conclude that:
voltage (V) versus the current (I) graphs
The above battery sends a current \( I_1 \) when \( R = R_1 \) and a current \( I_2 \) when \( R = R_2 \). Obtain the internal resistance of the battery in terms of \( I_1 \), \( I_2 \), \( R_1 \), and \( R_2 \).
Three wires A, B, and C of the same material have lengths and area of cross-sections as \( (2l, \frac{A}{2}) \), \( (l, A) \) and \( (\frac{l}{2}, 2A) \), respectively. If the resistances of these wires are \( R_A, R_B, R_C \) respectively, then:
Expression for internal resistance in terms of I1, I2, R1, R2:
A battery of emf E and internal resistance r is connected to an external resistance R.
(I) Expression for current I and maximum current:.
(II) Terminal voltage V and its maximum value:.
The figure shows the plot of current through a cross-section of wire over two different time intervals. Compare the charges Q1 and Q2 that pass through the cross-section during these time intervals.
plot of current through a cross-section
Derive an expression for the resistivity of a conductor in terms of number density of free electrons and relaxation time.
Two cells of EMFs \( E_1 \) and \( E_2 \), and internal resistances \( r_1 \) and \( r_2 \), are connected in parallel. Derive an expression for the EMF and internal resistance of the equivalent cell.
What is the difference between ‘emf’ and ‘terminal voltage’ of a cell?