09 physics in circuits and gadgets (part 1)

7/27/2019 09 Physics in Circuits and Gadgets (Part 1)

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Maria Carmela T. Garcia

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1st

semester 2013-2014

Why is it that when you walk on a carpeted floor andreach for a door knob, you sometimes get a littleshock?

Why do you sometimes get this same little shock whenyour arms bumps against your friend as you arewalking in the mall?

Why does your hair stand on end after removing your

cap on a cold day?

What causes lightning?


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www.school-for-champions.com

safe4work.orgscienceblogs.com

Atoms primarily consist of

Positively charged protons

Neutral neutrons

Negatively chargedelectrons that orbit the

nucleus at high speeds.

www.universetoday.com


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The charged particles electrons and protons have the same magnitudeof charge, which is

e = 1.6 10-19 C

www.universetoday.com

Some materials hold their electrons verytightly.

These materials are called insulators.

Other materials have some loosely heldelectrons, which move through them veryeasily.

These are called conductors.


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Positively

Charged

Uncharged/

Neutral

Negatively

Charged

More protons than

electrons

Equal number of

protons and electrons

More electrons than

protons

7198.185.178.104

Unit of Charge: Coulomb, C

Static electricity is the imbalance of positive andnegative charges.

Conservation of Charges

Charges are neither created nor destroyed.

Theytransferfrom one object to another.

Properties of Charges


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Quantization of Charges

Electric charge (Q) always occurs as some

integral multiple of the fundamental

charge e

Properties of Charges

Like charges REPEL, unlike chargesATTRACT

Holzner, Stephen. 2006. Physics for Dummies. Wiley Publishing


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Charged objects can also attractsomething that is neutral.

Holding it near a neutral object will makethe charges in that object realign.

corresponds to a

rearrangement of thebound electrons in the

material.


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There are three ways to charge an object

By friction

By conduction

By induction


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whs.wsd.wednet.edu


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tutorvista.com

When the air is very dry, it becomes lessconductive

When the air is humid, the water in the air allowsthe electrons to move off you more quickly


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http://scijinks.nasa.gov/lightning


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www.frankswebspace.org.uk

Weve talked about how like charges attract, and

unlike charges repel

The presence of an electric charge produces a

force on all other charges present.

The electric force produces action-at-a-

distance; the charged objects can influence each

other without touching.

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What is the repulsive force between twoelectrons that are 1m apart?

Electrically charged object generatean electric field in the space aroundit

This field exerts the pushes or pullsto other charged objects in the

surrounding area. The electric field is a vector field.

The electric field is

a vector field.


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f i e l d l i n e s n e v e r i n t e r s e c t !

f i e l d l i n e s n e v e r i n t e r s e c t ! f i e l d l i n e s n e v e r i n t e r s e c t !

f i e l d l i n e s n e v e r i n t e r s e c t !

http://2.bp.blogspot.com/-sEfvf1izXBo/TeZZNGTopmI/AAAAAAAAAKo/7s1k1eWpdg0/s1600/E_field.png


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Electric field is expressed in Newtons perCoulomb (N/C) and use the symbol E.

What is the magnitude of the electric fieldE at a field point 2.0 m from a point chargeq = 4.0 nC?


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09 physics in circuits and gadgets (part 1)

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