Current electricity is central to CBSE Class 12 and also forms the base for many JEE/NEET questions involving drift current, internal resistance, combinations of cells, and effective resistance/power in circuits. Mastery of these concepts helps you solve both numerical and conceptual problems quickly and accurately.
20
Minutes
15
Questions
1 / -0
Marking
Q1. A copper wire of radius carries a steady current of . The free electron density in copper is and the elementary charge is . Using , estimate the drift speed of electrons in the wire.
Q2. A conductor in the shape of a right circular cone of length has radius at one end and radius at the other. Its resistivity is and current flows along the axis between the two ends. By writing and using the linear variation of radius, the resistance between the ends is:
Q3. Two cells with emfs , and internal resistances , are connected in parallel and the combination is connected across an external resistor . What is the magnitude of the current through ? (Treat the parallel cells correctly by finding the equivalent Thevenin emf and internal resistance.)
Q4. Two identical cells each of emf and internal resistance are used to drive an external resistor . Let be the power delivered to when the cells are connected in series, and the power when they are connected in parallel. Which statement is correct?
for every value of .
if , if , and when .
if , and reverse if .
for all only if .
Q5. In a potentiometer experiment with a uniform wire and a driver of fixed emf, a test cell of emf gives a balancing length when connected open-circuit. When a load resistor is connected across the test cell, the balancing length becomes . Assuming the potential gradient along the wire is unchanged, the internal resistance of the test cell is:
Q6. A copper wire of radius carries a steady current of . The free electron number density in copper is . Using , the order of magnitude of the drift speed of electrons in the wire is closest to
Q7. Two straight uniform wires made of the same material have equal mass. Wire A has length and radius . Wire B has length . Each wire is separately connected across the same potential difference . If and are the currents through A and B respectively, the ratio is
Q8. A battery of emf and internal resistance is connected in series with resistors and . A voltmeter of resistance is placed across . The reading of the voltmeter (in volts) is approximately
Q9. Two identical filament bulbs, each of resistance , are connected in parallel across a battery of emf and internal resistance . Initially both bulbs glow. One filament fuses (becomes open) leaving the other intact. If is the power dissipated in one bulb before fusing and is the power dissipated in the remaining bulb after fusing, which statement is correct?
(the remaining bulb becomes twice as bright)
(brightness of the remaining bulb remains unchanged)
Q10. Twelve identical resistors each of resistance are placed along the edges of a cube. The equivalent resistance between two opposite vertices of the cube (across the space diagonal) is
Q11. A battery of emf and internal resistance is connected to an external resistor of . The heat produced per second (power dissipated) inside the battery due to its internal resistance is:
Q12. A battery of emf and internal resistance is connected to a variable resistor in series with two identical resistors each of resistance that are connected in parallel (the two are in parallel and that combination is in series with ). For what value of is the power dissipated in the variable resistor maximum?
Q13. Two identical cells, each of emf and internal resistance , are used to drive a load resistor . Compare the power dissipated in when (I) a single cell is used and (II) the two cells are connected in series across the same . Which statement is correct?
The power with two cells in series is greater than with a single cell but less than times the single-cell power (i.e., lies between and ).
The power with two cells in series is always exactly times the single-cell power.
The power with two cells in series is always exactly times the single-cell power.
The power with two cells in series is always less than the power with a single cell.
Q14. A cylindrical conductor of length has uniform resistivity , but its cross-sectional area varies linearly from at one end () to at the other end (). The resistance between the two ends is:
Q15. Consider an infinite network of identical resistors (each of resistance ) connected between terminals and as follows: from a resistor connects to node 1; from node 1 another resistor connects to node 2; and so on ad infinitum. Additionally, from each node there is a resistor that connects directly to terminal . The equivalent resistance between and is: