DAILY QUESTION REVIEW · 13 SEPTEMBER 2026
Resistance and temperature: first check the reference
In the September 13 daily set, 24 of 29 answered attempts on the verified question version did not match the stored key. But the wording left something important unstated: the temperature at which the coefficient applies. We should have stated that reference clearly. We need to explain it before interpreting the results.
The original question
A metallic wire has a resistance of 10 Ω at 20°C. If the temperature coefficient of resistance of the metal is 0.004 °C⁻¹, its resistance at 100°C will be:
A: 13.2 Ω · B: 14.0 Ω · C: 10.32 Ω · D: 6.8 Ω
Stored key: A, 13.2 Ω. The original wording above is preserved, with mathematical notation formatted for reading. It does not say “coefficient at 20°C”.
What the recorded answers show
For September 13 (IST), the verified form has 34 recorded first attempts: 29 answered and 5 explicit skips. Of the answered attempts, 5 matched the stored key and 24 did not: 24/29 = 82.76%. Skips are outside that denominator.
| Option | Count |
|---|---|
| A: 13.2 Ω | 5 |
| B: 14.0 Ω | 11 |
| C: 10.32 Ω | 7 |
| D: 6.8 Ω | 6 |
B was the most-selected option that did not match the key: 11/29 answered attempts (37.93%), or 11/24 key-mismatching attempts (45.83%). Four additional records with an unverified form are excluded: A: 2, C: 1, skip: 1.
These counts describe this set's records, not all NEET students. An option alone does not reveal a student's reasoning. Because the original wording is ambiguous, the mismatch rate does not establish how difficult the question is or prove that each mismatch was a conceptual error.
A clarified version for learning
This is a rewrite, not the question students saw: a wire has resistance 10 Ω at 20°C. Its temperature coefficient of resistance, referenced to 20°C, is 0.004 °C⁻¹. Using a linear resistance–temperature model, find its resistance at 100°C.
The model relates resistance at a temperature to resistance at its reference temperature. Use the coefficient for that reference. OpenStax: temperature dependence and resistance.
ΔT = 100 − 20 = 80°C
R₁₀₀ ≈ R₂₀[1 + α₂₀(100 − 20)]
R₁₀₀ ≈ 10[1 + 0.004 × 80] = 13.2 Ω
Under this stated assumption, 14.0 Ω can result from inserting 100 instead of the change of 80. That is a possible route to B, not evidence that all 11 people used it.
Why the missing reference matters
As an alternative interpretation, suppose 0.004 °C⁻¹ is referenced to 0°C. Within the same linear model, use both temperatures relative to zero:
R₁₀₀/R₂₀ = (1 + 0.004 × 100)/(1 + 0.004 × 20)
R₁₀₀ ≈ 10 × 1.4/1.08 ≈ 12.96 Ω
That value is not listed. This is an illustrative alternative assumption, not a claim that the original specified 0°C. A defensible interpretation deserves checking; students should not be blamed for information the question omitted. This explainer does not claim that the app's question or scoring has already been changed.
Take this into your next attempt
Write the reference temperature beside the coefficient before substituting numbers. If it is missing, flag the assumption you use.
Disagree with our answer? Explain your reasoning—we'll check it. Include the reference temperature and calculation you used. We will check reported errors and correct confirmed mistakes.
Counts are per account, not verified unique people; known staff/bot records excluded. Data cutoff: 14 September, 09:22 IST. Late or missing records remain possible. Display language was not recorded per attempt; no language-specific result is claimed.
Source and question version
Question record: daily-2026-09-13 · itm_3efd6a596a8ac5a7 · 2026.09.09-1411 · form 93bb11cf4ea79aae.
Original question and stored key: PrepArena archived set records. Explanation version: 1, 14 September 2026.