In-text Questions — Resistance and Resistivity — Electricity

1. 12 marksNCERT Cl-10 Science, In-text Qs after §11.5, Q1

   On what factors does the resistance of a conductor depend?

   Hint. There are four separate factors — two geometric, one material-based, one environmental.

   Step 1 — Recall the formula. R = ρl/A.

   Step 2 — Read off the factors. Resistance depends directly on length (l), inversely on cross-sectional area (A), and on the nature of the material (ρ, resistivity).

   Step 3 — Add the factor outside the formula. Resistance (and resistivity) also varies with temperature, since heating a conductor changes how freely its charges move.

   ✦ Answer: Length (directly), cross-sectional area (inversely), the material's resistivity, and temperature.

   Where students slip. Leaving out temperature — the formula R = ρl/A captures three factors directly, but the text separately notes that resistance also varies with temperature.

2. 22 marksNCERT Cl-10 Science, In-text Qs after §11.5, Q2

   Will current flow more easily through a thick wire or a thin wire of the same material, when connected to the same source? Why?

   Hint. Compare their cross-sectional areas, then connect that to resistance.

   Step 1 — Compare cross-sectional areas. A thick wire has a larger cross-sectional area than a thin wire of the same material and length.

   Step 2 — Apply R ∝ 1/A. Since resistance is inversely proportional to area, the thick wire has lower resistance.

   Step 3 — Connect resistance to current. With the same source (same V) and lower resistance, more current flows (I = V/R).

   ✦ Answer: Current flows more easily through the thick wire, since its larger cross-sectional area gives it lower resistance.

   Where students slip. Reasoning that a thick wire 'has more material to resist current' — resistance actually decreases with more cross-sectional area, the opposite of what that intuition suggests.

3. 32 marksNCERT Cl-10 Science, In-text Qs after §11.5, Q3

   Let the resistance of an electrical component remain constant while the potential difference across the two ends of the component decreases to half of its former value. What change will occur in the current through it?

   Hint. Ohm's law directly links current to potential difference when resistance is fixed.

   Step 1 — Recall Ohm's law. I = V/R.

   Step 2 — Apply the change. Since R stays constant and V is halved, I = (V/2)/R is also halved.

   ✦ Answer: The current also decreases to half of its former value.

   Where students slip. Assuming current stays the same because 'resistance is constant' — resistance being constant is exactly what makes current track potential difference proportionally, not what keeps current fixed.

4. 42 marksNCERT Cl-10 Science, In-text Qs after §11.5, Q4

   Why are coils of electric toasters and electric irons made of an alloy rather than a pure metal?

   Hint. There are two separate reasons — one about resistivity, one about durability under heat.

   Step 1 — Resistivity reason. Alloys generally have higher resistivity than their constituent metals, producing more heat for a given current.

   Step 2 — Durability reason. Alloys also do not oxidise (burn) readily even at high temperatures, which is why they last longer than many pure metals under repeated heating.

   ✦ Answer: Alloys have higher resistivity (generating more heat) and resist oxidising at high temperatures, making them more durable for repeated heating than a pure metal would be.

   Where students slip. Giving only the resistivity reason — the oxidation-resistance reason is equally part of the book's own explanation and shouldn't be left out.

5. 52 marksNCERT Cl-10 Science, In-text Qs after §11.5, Q5

   Use the data in Table 11.2 to answer the following – (a) Which among iron and mercury is a better conductor? (b) Which material is the best conductor?

   Hint. Lower resistivity means a better conductor — scan the table for the smallest values.

   Step 1 — Compare iron and mercury. Iron's resistivity (10.0 × 10⁻⁸ Ω m) is much lower than mercury's (94.0 × 10⁻⁸ Ω m).

   Step 2 — Apply the rule. Since lower resistivity means a better conductor, iron conducts better than mercury.

   Step 3 — Find the overall best conductor. Silver has the lowest resistivity in the whole table (1.60 × 10⁻⁸ Ω m).

   ✦ Answer: (a) Iron is the better conductor of the two. (b) Silver is the best conductor overall.

   Where students slip. Assuming mercury (a liquid metal) must conduct better — its resistivity in the table is actually almost ten times higher than iron's, making it the poorer conductor of the two.

Solutions written by the tuition.in editorial team and checked against the NCERT Class 10 Science textbook, Reprint 2026-27 (jesc111.pdf) — seven in-text question sets (23 questions total, not 16 as some older manifests claim) plus one end-of-chapter Exercise (18 questions, correctly counted). Unchanged by rationalisation. Table 11.2's resistivity values (used for several answers) were read directly from the book, including nichrome's 100 × 10⁻⁶ Ω·m.. Questions are referenced from the NCERT textbook for identification.