✓ Board-verified
Physics · 2025 · 2 marks
CBSE 2025 · Region 5 · Set 2 · Q18
A wire of resistance X ohm is gradually stretched till its length becomes twice its original length. If its new resistance becomes 40 Ω, find the…
A wire of resistance X ohm is gradually stretched till its length becomes twice its original length. If its new resistance becomes $\displaystyle 40 \Omega$, find the value of X.
Marking-scheme solution
$\displaystyle R=n^{2} x$
$\displaystyle 40=(2)^{2} x$
$\displaystyle x=10 \Omega$
OR
Volume of wire before and after stretching will remain the same:
$\displaystyle A_{1} l_{1}=A_{2} l_{2}$
$\displaystyle A_{2}=\frac{A l}{2 l}=\frac{A}{2}$
$\displaystyle R=\rho \frac{l_{2}}{A_{2}}$
$\displaystyle 40=4 \rho \frac{l}{A}$
$\displaystyle \therefore x=10 \Omega$
All Current Electricity questions2025 question paperNCERT solutions: Current ElectricityPractice Current Electricity →
More from Current Electricity
- A steady current flows through a metallic wire whose area of cross-section increases continuously from one end of the wire to the other. The…2023
- (i) Define mobility of electrons. Give its SI units. (ii) A steady current flows through a wire AB, as shown in the figure. What happens to the…2023
- What is the order of magnitude of drift velocity of electrons in a conductor? Deduce the relation between the current flowing through a conductor and…2026
- 'Current is a scalar quantity, although we represent current with an arrow.' Explain. Derive the balance condition of a Wheatstone Bridge.2026
- The number of electrons flowing through a conductor per second is 3 · 3 × 10^19. The current flowing through the conductor is:2023
- 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…2026
- Define current density and relaxation time. Derive an expression for resistivity of a conductor in terms of number density of charge carriers in the…2023
- A battery of e. m. f. 12 V and internal resistance 0.5 Ω is connected to a 9.5 Ω resistor through a key. The ratio of potential difference between…2025
CBSE Class 12 Physics past-paper question from the 2025 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.