Electric Charges and Electric Fields
Electric Charges and Electric Fields
How are Objects Electrostatically Charged
How are Objects Electrostatically Charged
Examples of Electrostatic Charges
Examples of Electrostatic Charges
Sample
State and Explain what Happens to small neural metal sphere (suspended from string) when a positively charged rod is brought close to it.
- by induction → electrons attracted to the left side of the sphere since unlike charge attract, leaving the right side partially charged.
- small sphere will swing towards the left since the forces of attraction between unlike charges > forces of repulsion between like charges
Important
make comparison between forces
- also important to say that if a particle undergoes charge separation, how the fact that the negative/positive charge is closer to the other object results in greater forces of electrostatic attraction/repulsion and is thus attracted/repelled from other object - refer to below example
Sample
Dust particle attracted to TV screen
- when dust particles are near the screen, electrons in the dust are attracted to the side closer to the screen as unlike charges attract
- results in charge separation in the dust particles
- as negatively charged region in dust particle is nearer to screen, force of attraction is greater than force of repulsion (electrostatic) with the positively charged region in the dust
- resulting in overall electrostatic force of attraction to the screen.
Motion of transferring electrons = current flow.
- the sphere will oscillate for this setup
Note
If battery is connected to 2 plates, side connected to positive terminal is positively charged and side connected to negative terminal is negatively charged
Important
Electrostatic Attraction:
- The positively charged ball attracts negative electrons to the near side of the neutral ball.
- This leaves behind positive charges on the far side of the neutral ball, due to electrostatic forces of attraction
Sample
To explain Attraction
- Positively charged metal rod attracts electrons in the uncharged metal sphere to the side of the sphere nearer the rod, leaving excess of positive charges on the opposite side.
- this charge separation causes stronger forces of attraction between negative electrons on the metal sphere and positively charged rod (which is closer) than the positively charged force of repulsion between positively charged regions resulting in sphere being attracted to rod.
Explain How Charges Could Cause Ignition / Be Dangerous
- when there is sudden discharge of the excess charges, such as when a conductor is placed near the fuel / aircraft / object → a spark could be produced, igniting the fuel
Note
When you have 2 forces acting on an object → state how the electrostatic forces of attraction/repulsion are greater/smaller than electrostatic forces of attraction/repulsion. Hence attracts/repels as unlike poles attract/like poles repel
if you have a strip, one part is closer to charged object → it will experience a greater force of attraction compared to the part further away from charged object → thus would bend. more number of electrons also means stronger attractive/repulsive forces.
Key Words
- can use NET negatively/positively charged
- charges redistribute uniformly
Sample
explain how experiment shows there is electric field around rod
- plastic rod able to exert force on charged object without contact