Electricity

The shocking introduction

Electrical charges

• Everything in the universe is made up of atoms

• Those atoms are made up of subatomic particles

• Three main ones:– Neutrons– Protons– Electrons

Electric Charges continued

• Neutrons have no electric charge• Protons have positive electric charge• Electrons have negative electric charge• Even though protons are much larger than

electrons, their charge is exactly EQUAL AND OPPOSITE.

Moving charges

• Whenever charges move around (from current in a wire to lightning strikes), it is always ELECTRONS that move.

• That’s pretty much it for this slide.

Attraction and Repulsion

• Like charges repel• Unlike charges attract• Draw on the situations below to show which

are positive and which are negative charges.

Charges and neutrality

• Pretty much anything that you’ll come across starts off electrically neutral.

• This is why you don’t shock yourself when you touch stuff in your daily life.

• Sometimes, objects acquire excess electrons. These objects then become NEGATIVELY charged.

• Other times, objects lose electrons. These objects then become Positively charged.

Charge imbalances

• If something has a charge imbalance, that means that it has more/less charge than usual.

• If two objects with UNLIKE amounts of charge come into contact, charge will move from one to the other until they are equal.

• What kind of charges move?

Conductors and Insulators

• Just like for heat, some materials are good electrical conductors and some are good electrical insulators.

• Usually, the same materials are good conductors of heat and electricity, for the same reason.

• Electrons in conductors are not held tightly to their atoms, so they can wander off

• Let’s look at a picture:

Conduction of Electricity

http://thephysicstutor.com/notes/images/conduction.png

Conductors

• An important thing about conductors:– Any extra charge is on the outside

• A solid conductor won’t have any charge in the middle

• The reason for this is that the charges all want to get away from themselves as much as they can.

Zapping stuff

• So, let’s say you acquire an excess of electrons (like, say, by shuffling your feet across a carpet).

• You now have a negative charge.• Your younger brother/sister has a neutral

charge.• When you sneak up behind them and touch

their ear, what happens? Why?• Try this at home!

Electric Force

• All charges exert forces on all other charges.• Like charges push each other away• Unlike charges attract each other.• The magnitude of the force depends on the

amounts of charge and the distance between them.

• However, a charged object can exert a force on something that is neutrally charged. Why?

Force between charged object and neutral object

• Let’s say you have a negatively charged object (left) that is brought near a neutrally charged object (center).

• The negative charge in the first object repels the negative charge on the second object to the other side, leaving the closer side with a positive charge.

• So they will attract, even though the second one was initially neutral.

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Charging by Induction

http://etudeallegro.com/tuition/images/stories/POL/induction-charging-all-steps.jpg

Charge Polarization

• Look at page 512 in your book• In insulators, charges can’t move around like

they can in conductors.• However, they still TRY to rearrange

themselves.• So even insulators can experience electrical

forces.