Electricity

The Basics

The flow of electricity is actually the flow of _______________.

A. Electrons B. Protons C. Electric chargeD. Energy

The flow of electricity is actually the flow of _______________.

A. Electrons B. Protons C. Electric chargeD. Energy

Electricity

• Its all based on atoms – protons and electrons.– Protons are positive +– Electrons are negative –

• If electrons move from one atom to another, the first atom becomes positive and the second atom becomes more negative

• Electric Charges follow a code– Like charges (+,+) repel each other– Opposite charges (+, -) attract each other

When a balloon is rubbed against your hair and pulled away, your

hair clings to it because _________.

A. Rubber is very stickyB. The balloon is filled with heliumC. The hair and balloon are both positively

chargedD. The hair is positively charged and the balloon is

negatively charged

When a balloon is rubbed against your hair and pulled away, your

hair clings to it because _________.

A. Rubber is very stickyB. The balloon is filled with heliumC. The hair and balloon are both positively

chargedD. The hair is positively charged and the balloon is

negatively charged

Static Electricity

• “Static electricity is caused any time two different materials come in contact and then separate

• Blanket in the winter• Shoes on the carpet

• Static electricity is present in almost all substances

• The greater the difference in charge the more likely a discharge will occur.

Rubbing your hair with a balloon increases the static charge because

____________.

A. Protons are moving from your hair to the balloon.

B. The balloon is getting charge from your hair.

C. The rubber in the balloon is non-conducting so it allows the electricity to gather

D. Hair and rubber are compatible

Rubbing your hair with a balloon increases the static charge because

____________.

A. Protons are moving from your hair to the balloon.

B. The balloon is getting charge from your hair.

C. The rubber in the balloon is non-conducting so it allows the electricity to gather

D. Hair and rubber are compatible

Conductor/Insulator

• Substances which allow for easy electric charge movement are conductors– Metal

• All other substances are non-conductors or insulators– Glass

• Some substances can be conductors sometimes and insulators other times and are called semiconductors– microchips

Electric wires are wrapped with rubber or plastic in order to keep you from being electrocuted. This is because

the rubber or plastic is a good _____________.

A. InsulatorB. Conductor C. Transfer pointD. Bridge for the electrons

Electric wires are wrapped with rubber or plastic in order to keep you from being electrocuted. This is because

the rubber or plastic is a good _____________.

A. InsulatorB. Conductor C. Transfer pointD. Bridge for the electrons

Electric Force

• Created when objects have a charge.• Amount of force depends on amount of

charge and distance to another charge• Electric force either pushes away (repels) or

attracts• Amber rubbed with fur picked up small bits of

wood and cloth

Electric Force: Coulomb’s LawElectric Force: Coulomb’s Law

• F = force ; q = charge; r = distance from centers

• SI Unit for electric charge is coulomb

• Coulomb’s Constant – kc=8.99 X 109 N x m2/C2

• F = force ; q = charge; r = distance from centers

• SI Unit for electric charge is coulomb

• Coulomb’s Constant – kc=8.99 X 109 N x m2/C2

2

21

r

qqkF

ce

If you put your finger 1 cm from the Vandegraff, it will be attracted to it. If you move your finger to 3 cm from the

VGG, the attraction _______.

A. Stays the sameB. Decreases by 3C. TriplesD. Decreases by 9

If you put your finger 1 cm from the Vandegraff, it will be attracted to it. If you move your finger to 3 cm from the

VGG, the attraction _______.

A. Stays the sameB. Decreases by 3C. TriplesD. Decreases by 9

If I double the charge on one of two objects, the overall impact to

the force is _________

A. Doubled B. HalvedC. Unchanged D. Quadrupled

If I double the charge on one of two objects, the overall impact to

the force is _________

A. Doubled B. HalvedC. Unchanged D. Quadrupled

Gravity vs Electricity

• Gravity– Attractive – Based on distance and mass– Weak force

• Electricity– Attractive or repulsive– Based on distance and charge– Strong force

An object that does not allow electricity to flow is called an

insulator.

A. TrueB. False

An object that does not allow electricity to flow is called an

insulator.

A. TrueB. False

Charge Quantization

• Charge cannot take any arbitrary values• It can only have values that are integral multiples of the

fundamental charge (charge of proton/electron)• The fundamental charge is e = 1.602×10−19 coulombs• Quarks (what makes protons, neutrons and other Hadrons) do

have 1/3 e or 2/3 e but they have never been isolated, they always come as pairs (muons) or triplets (baryons), so they don’t violate the fundamental charge rule.

• You must know to challenge any claim on the AP test if they suggest that a charge do not follow this rule!!!