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Chapter 19: Electric Charges and Currents

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1 Chapter 19: Electric Charges and Currents
19-2: Static Electricity

2 Electric Charge All matter is made up of atoms, and atoms are made up of tiny particles called protons, neutrons, and electrons. Both protons and electrons have a basic property called charge - protons are positive and electrons are negative.

3 Charge and Force A force of attraction pulls objects together - this exists between 2 oppositely charged particles (negative-positive) A force of repulsion pushes objects apart - this exists between 2 like charges (neg-neg, pos-pos)

4 Like charges repel each other, unlike charges attract each other
Rule for Charges: Like charges repel each other, unlike charges attract each other

5 Electric Field Definition: the arrangement of field lines that determine the force per unit charge a small stationary charge would experience at each point in space The pattern of an electric field depends on the number, size, sign, and location of charges. The electric field is visualized by showing lines of force Force is stronger where lines are closer together - occurs when charges are close The direction of the force depends on whether the placed charge is positive or negative

6 Electric Field - Like Charges

7 Electric Field - Unlike Charges

8 Electric Field - Charges

9 19-2: Static Electricity Electrons may be loosely held to their atoms - so they can easily be separated from their atoms. An entire object can acquire a charge A neutral object acquires an electric charge when it either gains or loses electrons.

10 Methods of Gaining or Losing Charges:
Friction: removes the charges from an object and places them on another object.

11 Methods of Gaining or Losing Charges:
Conduction: electrons flow through one object to another by direct contact.

12 Methods of Gaining or Losing Charges:
Induction: charges are rearranged and line up in different positions.

13 Conductors and Insulators
Conductors: material which permits electrons to flow freely or transfers heat more easily than other substances. Ex: metals – silver, copper, aluminum Insulators: material made up of atoms with tightly bound electrons that are unable to flow freely – do not conduct electric charges well Ex: rubber, glass, wood, plastic, dry air Polarized: partial alignment of negative and positive charges in molecules in response to an electric field

14 Electric Discharge Transfer of electrons from one object to another results in a static charge on each object. Static electricity is the build up of unbalanced electric charges on an object Electrons that move from one object to another eventually leave the object Electric discharge: loss of static electricity as electric charges move off an object

15 Lightning Charges separate within the thunderclouds
There is a build up positive and negative charges in different parts of the cloud Objects on Earth become electrically charged by induction Charges move away from the cloud, positive charges are left closest to ground – transfer of electrons is lightning Lightning can be cloud to cloud Thunder is the expansion of air from the heat produced by lightning

16 Lightning Rods and Grounding
Benjamin Franklin – lightning rods Grounding: the Earth is extremely large and is a good conductor of electric charge. Earth can easily accept or give up electric charges. Lightning rod is put on top of buildings. A wire is run from the rod to the ground where lightning can pass through safely. The charge then goes into Earth.

17 Lightning Rods and Grounding

18 Electroscope Can detect electric charges
Consists of 2 leaves, a metal knob, and a metal rod A charge is put onto the knob which then flows down the metal rod into the leaves separating them. If an electroscope is touched by a negative charge, the negative charge flows down the rod into the leaves, giving both leaves a negative charge and causing them to separate (like charges repel). Same thing will happen if a positive charge is put to the electroscope.

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