Lesson 3.1 - Electric Nature of Matter

VIDEO LESSON (42:55 min)
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GRADE 9 REVIEW

  • Matter is composed of charged and uncharged subatomic particles 
    • Electrons (negative)
    • Protons (positive)
  • Electrons are weakly bound to atoms and are able to move around (POSITIVE PROTONS DO NOT MOVE!)
  • Moving electrons is the basis of electricity (Static and Current)

LAW OF ELECTRIC CHARGES
  •  Like charges repel


  • Opposite charges attract


COULOMB'S LAW



Note: Strictly speaking this law is only valid for point charges. However, we can mathematically prove that any distribution of charge can act like a point charge at the centre of the charge distribution when viewed from the outside (using calculus).

RECALL


EXAMPLE PROBLEM #1

Determine the force between two \( 5.0 \mu C \) charges that are \( 15 cm \) apart if:
a) they are the same charge.
b) they have different charges.

SOLUTION:




EXAMPLE PROBLEM #2

An object with a \( +3.0 \mu C \) charge and one with a \( -5.0 \mu C \) charge are some distance apart and they exert a \( 2.0 N \) force on each other. They are then touched together and placed at the same distance. What is the new force between the two objects.

SOLUTION:



EXAMPLE PROBLEM #3

Three charges are placed according to the diagram below

What is the net force on C?

SOLUTION:



EXAMPLE PROBLEM #4

Two identically charged spheres (\( 2.0 \times 10^{-8} C \)) with mass of \( 1.0 g \). One is fixed and the other is attached to a string and is deflected by some angle when the charges are \( 3.0 cm \) apart. What is the angle of deflection?

SOLUTION:

 


Sửa lần cuối: Thứ hai, 19 Tháng 5 2025, 9:15 PM