Home › Tamil Nadu SSLC (Class 10) › Physics › Electricity › A wire of resistance 10 ohm is stretched uniform…
A wire of resistance 10 ohm is stretched uniformly until its length becomes three times the original. What is its new resistance?
A3.3 ohm
B90 ohm
C30 ohm
D270 ohm
Answer & Solution
Correct answer: B. 90 ohm
1. List the data: original $R = 10\,\Omega$, new length $= 3L$, same volume of wire.
2. Since volume is constant, if length becomes $3L$ then area becomes $A/3$.
3. Resistance formula is $R = \rho \dfrac{L}{A}$.
4. So $R' = \rho \dfrac{3L}{A/3} = 9\,\rho\dfrac{L}{A} = 9R$.
5. Hence $R' = 9 \times 10 = 90\,\Omega$.
6. Trap A (3.3) only divides by 3; trap B (30) multiplies length by 3 but ignores the area change; trap D (270) over-multiplies by an extra factor of 3.
_Source: Samacheer Kalvi (TN SCERT) Class 10 Science, Unit 4 Electricity "Electricity", p.64_
Related questions
A charged comb picks up small pieces of paper that carry no net charge, because the paper Compared with the tiny nucleus, the electrons around it form a cloud that is:Benjamin Franklin explained early observations by supposing that one type of charge stayedA test charge or a source charge moves, and as a result the force between them:If the two ends of a dipole can be pulled apart, induction can create charged objects withPlaced in a uniform field, such a dipole experiences a turning effect that changes its angTwo equal and opposite charges separated by a small distance form a dipole, characterised Where those lines are packed more densely, the field is: