STATIC ELECTRICITY

STATIC ELECTRICITY

THE STUDY OF CHARGES AT REST

KEY TOPICS

• ELECTRICAL CHARGES

• COULOMB’S LAW

• POLARIZATION

• ELECTRIC FIELD

• LIGHTNING

ELECTRICAL PHENOMENA

• ALL MATTER IS MADE FROM CHARGED PARTICLES

• THE ELECTRICAL PHENOMENA THAT WE EXPERIENCE IS DUE TO THE PRESENCE AND MOVEMENT OF COLLECTIONS OF ELECTRONS

RECOMMENDED ACTIVITY

MODEL OF AN ATOM – AIMS Activity

PhET SIMULATION

THE PhET SIM CALLED “JOHN TRAVOLTAGE” CAN BE USED TO SHOW HOW WALKING ACROSS A CARPET MIGHT CAUSE YOU TO GET A SHOCK

STATIC ELECTRICITY

• WHEN YOU RUB A BALLOON (OR STYROFOAM) ON YOUR HAIR, YOU SCRAPE ELECTRONS FROM THE ATOMS IN THE BALLOON ONTO YOUR HAIR

• THE ATOMS IN RUBBER AND STYROFOAM HAVE A STRONGER ATTRACTION FOR SOME OF THE ELECTRONS THAN THOSE IN YOUR HAIR

STATIC ELECTRICITY

• RUBBING AN OBJECT MADE OF RUBBER WITH HAIR IS A STANDARD PRACTICE FOR PRODUCING AN OBJECT THAT HAS AN EXCESS OF ELECTRONS

• AN OBJECT IN THIS CONDITION POSSESSES AN OVER ALL NET NEGATIVE CHARGE

STATIC ELECTRICITY

• OBJECTS CAN POSSESS A NET POSITIVE CHARGE IF THEY LOSE ELECTRONS

• OBJECTS CAN HAVE A NET POSITIVE OR NEGATIVE CHARGE IF THEY POSSESS A DEFICIENCY OR AN EXCESS OF ELECTRONS

• AN OBJECT IS SAID TO BE NEUTRAL IF THERE IS NO DEFICIENCY OR AN EXCESS OF ELECTRONS

VIDEO

TWO STYROFOAM CUPS CAN BE MADE TO REPEL EACH OTHER IF THEY BOTH POSSESS A NET NEGATIVE CHARGE

“Laws of Attraction”

Opposite Charges Attract

Like Charges Repel

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PhET SIMULATION

THE PhET SIM CALLED “ELECTRIC FIELD OF DREAMS” CAN BE USED TO SHOW HOW CHARGED PARTICLES INTERACT

LIKE CHARGES REPEL AND UNLIKE CHARGES ATTRACT

A COULOMB

• THE FUNDAMENTAL UNIT OF CHARGE

• IT IS EQUAL TO THE CHARGE OF 6.25 BILLION BILLION ELECTRONS

COULOMB’S LAW

ELECTRICAL FORCE BETWEEN TWO OBJECTS DEPENDS ON THE AMOUNT OF CHARGE ON EACH OBJECT AND THE DISTANCE BETWEEN THE OBJECTS

COULOMB’S LAW

• IF THE AMOUNT OF THE CHARGES IS GREATER, THE FORCE IS GREATER

• IF THE DISTANCE IS LESS, THE FORCE IS GREATER

VIDEO

• A STYROFOAM CUP THAT POSSESSES A NET NEGATIVE CHARGE WILL PICK UP VERY SMALL OBJECTS THAT POSSESS NO EXCESS CHARGE

• THIS CAN ONLY BE EXPLAINED BY POLARIZATION

PhET SIMULATION

THE PhET SIMULATION “BALLOONS AND STATIC ELECTRICITY” PROVIDES A VERY GOOD DEMONSTRATION OF HOW BALLOONS CAN PICK UP EXCESS ELECTRONS AND THEN EITHER BE REPELLED BY OR ATTRACTED TO OTHER OBJECTS

Polarization

• Polarized objects have an uneven distribution of charge.

• A polarized object has no net charge.

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Strong Force

Weak Force

FORCE AT A DISTANCE

• ELECTRICAL, MAGNETIC AND GRAVITATIONAL FORCES UPON OBJECTS HAVE SOMETHING IN COMMON

• THESE FORCES CAN BE APPLIED EVEN THOUGH THE OBJECTS INVOLVED ARE AT A DISTANCE FROM EACH OTHER

• CHILDREN HAVE A PROBLEM UNDERSTANDING THESE KINDS OF FORCES, BECAUSE THEY EXPECT OBJECTS TO BE IN CONTACT WHEN THEY EXERT A FORCE ON EACH OTHER

GRAVITY

THE CONCEPT OF GRAVITATIONAL FIELD IS OFTEN USED TO SHOW HOW THE EARTH CAN EXERT GRAVITATIONAL FORCES ON OBJECTS

ELECTRIC FIELD

THE CONCEPT CALL “ELECTRIC FIELD” WAS DEVELOPED TO HELP EXPLAIN HOW OBJECTS WITH ELECTRIC CHARGES CAN HAVE FORCES APPLIED TO THEM

PhET SIMULATION

THE PhET SIM CALLED “ELECTRIC FIELD OF DREAMS” CAN BE USED TO SHOW THE ELECTRIC FIELD NEAR A CHARGED PARTICLE

THE FIELD POINTS AWAY FROM A POSITIVE PARTICLE AND IS STRONGER NEAR THE PARTICLE

LIGHTNING

LIGHTNING IS AN ELECTRICAL DISCHARGE FROM CLOUDS THAT POSSESS A NET CHARGE

THE AIR THROUGH WHICH THE DISCHARGE OCCURS IS HEATED AND RAPIDLY EXPANDS TO CAUSE LIGHT AND SOUND

LIGHTNING

• CLOUD TO GROUND– THE CLOUD POLARIZES THE GROUND

AND THE DISCHARGE OCCURS WHERE THE CHARGE SEPARATION ON THE GROUND IS A MAXIMUM

• CLOUD TO CLOUD– IF CLOUDS POSSESS OPPOSITE

CHARGES, A DISCHARGE CAN OCCUR BETWEEN THEM

SUMMARY

• ELECTRICAL CHARGES– THE ATOM

• COULOMB’S LAW– ELECTRICAL FORCES

• POLARIZATION– CHARGES ATTRACT NEUTRAL OBJECTS

• ELECTRIC FIELD– FORCE AT A DISTANCE

• LIGHTNING– CHARGES IN CLOUDS