Distribution of ChargeDistribution of Charge

ElectroscopeElectroscopeSpherical vs. Irregular shaped Spherical vs. Irregular shaped

objectsobjectsLightning and Lightning rodsLightning and Lightning rods

The ElectroscopeThe Electroscope

A device that can be used to detect the A device that can be used to detect the presence of a nearby electrostatic chargepresence of a nearby electrostatic charge

Diagram:Diagram:

The ElectroscopeThe Electroscope

The electroscope can be charge by The electroscope can be charge by contact or by inductioncontact or by induction

Diagram of Charging by induction:Diagram of Charging by induction:Step 1:Step 1: Step 2: Step 2: groundinggrounding Step 3:Step 3:

Distribution of ChargeDistribution of ChargeThree RulesThree Rules to determine the location of charges to determine the location of charges

1.1. Charge is EVENLY DISTRIBUTED over the Charge is EVENLY DISTRIBUTED over the surface of a conducting spheresurface of a conducting sphere

Like charges repel, and want to get as far away from Like charges repel, and want to get as far away from each other as possible! each other as possible!

If charging by contact, the charged objects will have If charging by contact, the charged objects will have identical charge if the objects are identical. identical charge if the objects are identical. Otherwise, all we can be certain of is that the charge Otherwise, all we can be certain of is that the charge TYPE (- or +) will be the same.TYPE (- or +) will be the same.

2.2. Charge is ONLY found on the outside of a Charge is ONLY found on the outside of a conductor—there is no charge on the inside of conductor—there is no charge on the inside of a conducting materiala conducting material

Distribution of ChargeDistribution of Charge

Distribution of ChargeDistribution of ChargeThree RulesThree Rules to determine the location of charges to determine the location of charges

3.3. For irregular shaped conductors, the charge For irregular shaped conductors, the charge accumulates in regions of greatest curvatureaccumulates in regions of greatest curvature

For example, the sharpest point on an object will For example, the sharpest point on an object will collect the most chargecollect the most charge

Lightning!Lightning!Thunderstorms typically involve large Thunderstorms typically involve large

storm clouds that have strong updrafts and storm clouds that have strong updrafts and downdraftsdowndrafts

These up and down wind currents carry These up and down wind currents carry rain drops and hailstones up and down rain drops and hailstones up and down within the cloudwithin the cloud

Collisions between all the hailstones, etc. Collisions between all the hailstones, etc. cause the ionization of particles in the cause the ionization of particles in the clouds…For some reason, the negative clouds…For some reason, the negative charges tend to collect near the bottom of charges tend to collect near the bottom of the cloudthe cloud

Lightning!Lightning!

The strong negative charges in the cloud The strong negative charges in the cloud induces positive charges in the ground induces positive charges in the ground below the cloud:below the cloud:

When the charge buildsWhen the charge buildsup enough, the cloud up enough, the cloud will discharge in one of will discharge in one of three ways, dependingthree ways, dependingon what the closest on what the closest &/or easiest discharge &/or easiest discharge path is:path is:

Lightning!Lightning!

1.1. Cloud to groundCloud to ground: Discharge between the : Discharge between the bottom of the cloud and the closest and/or bottom of the cloud and the closest and/or most positively charged point on the groundmost positively charged point on the ground

- typically a pointed object, like a tree, a - typically a pointed object, like a tree, a steeple, TV antenna, etc.steeple, TV antenna, etc.

2.2. In-CloudIn-Cloud: Discharge occurring between the : Discharge occurring between the top and the bottom of the cloudtop and the bottom of the cloud

3.3. Cloud-to-CloudCloud-to-Cloud: Discharge between the : Discharge between the negative charges in one cloud and the positive negative charges in one cloud and the positive charges in another nearby cloudcharges in another nearby cloud

Lightning RodsLightning Rods Invented in the 1700’s in order to protect Invented in the 1700’s in order to protect

homes/barns/churches, etc. from lightning homes/barns/churches, etc. from lightning strikesstrikes

Lightning is “attracted” to tall pointed objects. If Lightning is “attracted” to tall pointed objects. If this happens to be the top of a house, then the this happens to be the top of a house, then the electricity will go through the house to get to the electricity will go through the house to get to the ground…typically starting a fireground…typically starting a fire

Lightning rods are designed to attract the Lightning rods are designed to attract the lightning strikeslightning strikes The lightning rods are made of pointed metal (like The lightning rods are made of pointed metal (like

copper, which is a great conductor) that is placed copper, which is a great conductor) that is placed above the highest point on a buildingabove the highest point on a building

The rod is connected with a strong conducting wire to The rod is connected with a strong conducting wire to a metal stake or plate, typically buried deep in the a metal stake or plate, typically buried deep in the groundground