Q14
1 markMCQSection A

Assertion (A): At high temperatures, metal wires have a greater chance of short circuiting.

Reason (R): Both resistance and resistivity of a material vary with temperature.

Electricity
Factors on which the Resistance of a Conductor Depends

Options

(i)Both (A) and (R) are true and (R) is correct explanation of the assertion (A).
(ii)Both (A) and (R) are true, but (R) is not the correct explanation of the assertion (A).
(iv)(A) is false, but (R) is true.
(iii)(A) is true, but (R) is false.
Official Answer

Option ii is correct.

insulation meltsshort circuitresistance and resistivity vary with temperaturenot the correct explanation

Marking Scheme

  • 10.5 marks for evaluating the truth value of Assertion and Reason.
  • 20.5 marks for correctly identifying that Reason is not the correct explanation of Assertion.

Hint

Think about what causes a short circuit (insulation failure) versus how resistance/resistivity of the metal itself changes with temperature.

Quick Oral Answer

Assertion is true because high temperatures melt the wire insulation, leading to direct contact (short circuit). Reason is also true because resistance and resistivity of metals increase with temperature, but this variation does not explain the melting of insulation.

Analysis & Explanation

  • Why Option ii is correct:
  • Assertion (A) is true: At high temperatures, the insulating cover (like PVC) of electrical wires can melt. This allows the live and neutral wires to come into direct contact, resulting in a short circuit. Thus, high temperatures increase the risk of short circuiting.
  • Reason (R) is true: The NCERT text states, 'Both the resistance and resistivity of a material vary with temperature.'
  • Explanation connection: While both statements are scientifically correct, the variation of a metal's resistance/resistivity with temperature does not explain why wires short circuit at high temperatures (which is due to insulation failure). Thus, (R) is not the correct explanation of (A).
  • Why other options are incorrect:
  • Option i: Incorrect because (R) is not the correct explanation of (A).
  • Option iii: Incorrect because (R) is true.
  • Option iv: Incorrect because (A) is true.

Common Mistakes

  1. 1Assuming that the change in resistance of the metal wire directly causes the short circuit.
  2. 2Thinking that resistivity variation with temperature is false.

Interesting Facts

Short circuits can cause extremely high currents to flow, leading to sparks, fires, and explosions if safety devices like fuses or circuit breakers are not present.

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2020?

This question carries 1 mark in the CBSE Class 10 Science 2020 examination.

Which chapter does this question come from in Science?

This question is from the chapter "Electricity" in the CBSE Class 10 Science syllabus.

What topic does this question cover in Science?

This question covers the topic "Factors on which the Resistance of a Conductor Depends" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2020 paper?

This is a MCQ question from Section A in the CBSE Class 10 Science 2020 paper.