A 50Ω resistance wire is stretched such that its length is doubled and its cross section area becomes half. The new resistance is:
Correct answer: B. 200Ω
- A. 100Ω
- B. 200Ω
- C. 50Ω
- D. 150Ω
Explanation
The resistance R of a wire is given by the formula: R = ρL/A, where ρ is the resistivity, L is the length, and A is the cross-sectional area. When the wire is stretched such that its length doubles and its cross-sectional area is halved, the new length L' is 2L and the new area A' is A/2. The new resistance R' is given by:R' = ρ(2L)/(A/2) = 4ρL/A = 4RTherefore, the new resistance is four times the original resistance, which means R' = 4 * 50Ω = 200Ω.Options A (100Ω) and D (150Ω) are incorrect as they do not correctly account for the quadrupling of resistance. Option C (50Ω) is incorrect because it suggests no change in resistance, which is not possible under these conditions.
This question appeared on the ETEA MDCAT 2008 paper, which you can sit online with every answer explained.
Report an error
The more specific you are, the faster it gets fixed. A source beats an opinion.
Prefer email? [email protected]
About Resistance and Resistivity
Resistance measures opposition to current in a conductor and follows R = V/I for an ohmic conductor, while resistivity is an intrinsic property of the material. Questions use R = ρL/A, examine effects of length, cross-sectional area and temperature, and distinguish resistance, resistivity, conductance and conductivity.
Practise Current Electricity
1,052 free Current Electricity MCQs from Physics, each with the correct answer and an explanation. Unlimited attempts, no account needed.
Discussion
Stuck on an option, or know a faster way to get there? Ask or explain it here.
No comments yet. Be the first to explain this one.
Exams that ask Physics questions like this
Physics is on 16 papers prepared for on TestUstad, and all of them draw the same bank, so this question is worth knowing for every one of them.
More Resistance and Resistivity questions
Ohm's law is valid only for currents following in:
The resistance of the three arms of the balanced wheat stone bridge is 50 ohms. The resistance in the 4 ohm range is:
The unit of conductance is
An efficient voltmeter has:
The two metals having the same resistance can be differentiated by their value:
A wir of uniform cross section A, length I and resistance R is cut into two equal pieces. The resistivity of each piece will be