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NCERT Class 10 Science Electricity: In-text questions (page 181) Solutions

Step-by-step working for every question of In-text questions (page 181) in NCERT's Class 10 Science book, chapter “Electricity”, written by Shishya. Each question is in our own short words; open the NCERT chapter for the exact wording and figures.

1. In-text (page 181) Q1

   On what factors does the resistance of a conductor depend?

   1. The resistance of a conductor depends on its length, cross-sectional area, material, and temperature.
   2. Resistance is directly proportional to the length of the conductor.
   3. Resistance is inversely proportional to the cross-sectional area of the conductor.
   4. Different materials have different resistivities, which affect the total resistance.
   5. For most conductors, resistance increases as the temperature rises.

   Answer: Resistance depends on length, cross-sectional area, nature of material, and temperature.

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2. In-text (page 181) Q2

   Does current flow more easily through a thick or a thin wire of the same material on the same source? Why?

   1. Resistance of a wire is directly proportional to its length and inversely proportional to its cross-sectional area.
   2. A thick wire has a larger cross-sectional area compared to a thin wire of the same length and material.
   3. Since resistance is inversely proportional to area, the thick wire has lower resistance than the thin wire.
   4. According to Ohm's law, current is inversely proportional to resistance for a constant voltage source.
      why?

      Ohm's law: at a steady temperature the current through a conductor is proportional to the potential difference across it, so V = IR (R = V/I, I = V/R).

   5. Therefore, current flows more easily through the thick wire because it offers less opposition to the flow of charge.

   Answer: Current flows more easily through a thick wire because it has a larger cross-sectional area, which results in lower resistance.

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3. In-text (page 181) Q3

   If the resistance of a component stays the same and the potential difference across it is halved, what happens to the current?

   1. According to Ohm's law, the current I flowing through a conductor is directly proportional to the potential difference V across it when resistance R is constant.
      why?

      Ohm's law: at a steady temperature the current through a conductor is proportional to the potential difference across it, so V = IR (R = V/I, I = V/R).

   2. The relationship is expressed as I = V ÷ R.
      why?

      Ohm's law: at a steady temperature the current through a conductor is proportional to the potential difference across it, so V = IR (R = V/I, I = V/R).

   3. Let the initial potential difference be V and the initial current be I₁ = V ÷ R.
   4. When the potential difference is halved, the new potential difference becomes V/2.
   5. The new current I₂ is calculated as (V/2) ÷ R.
   6. This simplifies to I₂ = (1/2) × (V ÷ R).
   7. Since I₁ = V ÷ R, the new current I₂ is equal to I₁ ÷ 2.
   8. Therefore, the current through the component is also halved.

   Answer: The current is halved.

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4. In-text (page 181) Q4

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

   1. Alloys have a higher resistivity than pure metals, which allows them to produce more heat for the same current.
      why?

      R = ρl/A: a wire's resistance grows with its length and falls as its cross-section grows; ρ (resistivity) depends only on the material and temperature.

   2. Alloys have a higher melting point than pure metals, so they do not melt when they get very hot during use.
   3. Alloys do not oxidize easily at high temperatures, which makes them last longer than pure metals in hot appliances.
      why?

      Oxidation is gain of oxygen (or loss of hydrogen); reduction is loss of oxygen (or gain of hydrogen). In a redox reaction one substance is oxidised while another is reduced.

   Answer: Coils are made of alloys because they have high resistivity, high melting point, and do not oxidize easily at high temperatures.

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5. In-text (page 181) Q5

   Using Table 11.2 (resistivities): (a) which is a better conductor, iron or mercury? (b) Which material is the best conductor?

   Uses a figure printed in the NCERT book — open the chapter above to see it.

   1. (a) Look at the resistivity values in Table 11.2 for iron and mercury.
      why?

      R = ρl/A: a wire's resistance grows with its length and falls as its cross-section grows; ρ (resistivity) depends only on the material and temperature.

   2. Iron has a resistivity of 0.000000010 Ω m.
      why?

      R = ρl/A: a wire's resistance grows with its length and falls as its cross-section grows; ρ (resistivity) depends only on the material and temperature.

   3. Mercury has a resistivity of 0.00000098 Ω m.
      why?

      R = ρl/A: a wire's resistance grows with its length and falls as its cross-section grows; ρ (resistivity) depends only on the material and temperature.

   4. Since iron has a lower resistivity than mercury, it offers less opposition to current flow.
      why?

      R = ρl/A: a wire's resistance grows with its length and falls as its cross-section grows; ρ (resistivity) depends only on the material and temperature.

   5. Therefore, iron is a better conductor than mercury.
   6. (b) Compare the resistivity values of all materials listed in Table 11.2.
      why?

      R = ρl/A: a wire's resistance grows with its length and falls as its cross-section grows; ρ (resistivity) depends only on the material and temperature.

   7. Silver has the lowest resistivity value of 0.000000016 Ω m.
      why?

      R = ρl/A: a wire's resistance grows with its length and falls as its cross-section grows; ρ (resistivity) depends only on the material and temperature.

   8. A lower resistivity indicates a better conductor.
      why?

      R = ρl/A: a wire's resistance grows with its length and falls as its cross-section grows; ρ (resistivity) depends only on the material and temperature.

   9. Thus, silver is the best conductor among the listed materials.

   Answer: (i) Iron is a better conductor than mercury; (ii) Silver is the best conductor.

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