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Electricity — Science STD 10 — Question

CBSE BoardEnglish MediumSTD 10ScienceElectricity5 Marks
Question
  1. What is meant by saying that the potential difference between two points is 1 volt? Name a device that helps to measure the potential difference across a conductor.
  2. Why does the connecting cord of an electric heater not glow hot while the heating element does?
  3. Electrical resistivities of some substances at $20^{0}\text{C}$ are given below:
Silver $1.60\times10^{-8} \Omega \text{ m}$
Copper $1.62\times10^{-8} \Omega \text{ m}$
Tungsten $5.20\times10^{-8} \Omega \text{ m}$
Iron $10.0\times10^{-8} \Omega \text{ m}$
Mercury $94.0\times10^{-8} \Omega \text{ m}$
Nichrome $100\times10^{-6} \Omega \text{ m}$
Answer the following questions in relation to them:
  1. Among silver and copper, which one is a better conductor? Why?
  2. Which material would you advise to be used in electrical heating devices? Why?
✓

Answer

  1. When 1 joule of work is done to move a charge of 1 coulomb from one point to another.
Device - Voltmeter.
  1. The heating element of the heater is made up of alloy which has very high resistance so when current flows through the heating element, it becomes too hot and glows red. But the resistance of cord which is usually of copper or aluminum is very law so it does not glow.
  2.  
  1. Silver is the best conductor of electricity and heat among all metals as it has more number of free electrons in the outermost shell. Its resistivity $\left(1.60 \times 10^{-8} \Omega m\right)$ is less than copper $\left(1.62 \times 10^{-8} \Omega m\right)$. Of couse, silver is the best conductor of electricity. Still, we find use of copper on a large scale in domestic wiring because silver is quite expensive.
  2. Nichrome is the best material for heating elements. It is because the resistivity of the nichrome is more than the resistivities of the metals used to make it and it does not oxidise at higher temperature.

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