Solve this question 18,19,20

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 Ans. 18-
An electrical conductor is a substance in which electrical charge carriers, usually electrons, move easily from atom to atom with the application of voltage .
Five conductor example
  1. Copper
  2. iron
  3. silver
  4. Gold
  5. Aluminium

Ans. 19

Universal law of gravitation- Every particle in the universe attracts every other particle by a force along a line joining them. The force is directly proportional to product of their masses and inversely proportional to the square of distance between them.

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