11.8: Electric Discharge
pg. 492
Key Concepts:
1. Electric discharge can be harmful and must be treated with caution.
Electric Discharge: the rapid transfer of electric charge from one object to another.
- The sudden transfer of static charge could damage sensitive electronic equipment.
- When a negative or positive charged object touches a sensitive electronic device, a
static discharge is released.
- When two opposite charged object are brought together, a rapid discharge of electrons
occurs.
- Charges always occur from negatively charged objects to positively charged objects.
- The greater the charge imbalance the more noticeable the discharge.
- Rubbing your feet on a rug in a dry room and then touching a metal door knob, you will
see and feel a static discharge. Turn off the lights and you can see the sparks.
Figure 2: Charged objects, such as; the door handle in a) , can cause electric discharge.
In b), coming close to the negatively charged handle enables the excess electrons to be
transferred to the hand, producing an electric discharge. c) After the discharge, the
imbalance of electrons between the hand and the handle is gone.
Lightning
- Lightning is the electric discharge between the clouds and the Earth’s surface.
- Water molecules in the cloud rub together and become negatively charged. The water
droplets move to the lower portions pf the clouds.
- The Earth has a neutral charge.
- The negative charged clouds force the Earth’s surface to become positively charged as
the electrons in the ground move further away.
- If the difference is sufficient enough a static discharge occurs from the clouds to the
ground, creating lightning.
- The air becomes super heated and light and sound are produced.
- Lightning can also occur between clouds.
Figure 3: Lightning is an electric discharge that occurs between clouds or between
clouds and the ground.
Lightning Rods
- Lightning is dangerous to buildings and people.
- Metal (Copper or Iron) Lightning rods are placed on buildings at their highest points.
- Lightning will strike the highest conducting point. The lightning rod is wired to the
ground.
- The electrical discharge will travel down the lightning rod to the conducting wire
directly into the ground.
Figure 6: Lightning rods are common on homes and barns in the country, where large
open areas make these buildings more vulnerable to lightning strikes.
Evidence of Learning …. Students can
- understand how electric discharges occur.
- cite and explain examples of the problems or dangers posed by electric discharge.
- cite and explain the operation of several common antistatic devices.
- describe the basic causes of lightning and explain how lightning rods work.
Check Your Learning
Questions 1 – 5, page 495
Summary:
- An electric discharge is the rapid transfer of electrons from one object to another.
- Electric discharges can produce visible sparks.
- Lightning is a visible and dramatic electric discharge.
- Lightning rods are used to safely direct lightning into the ground.