1. Electricity
Physical Science

2. 20.1 – Electric Charge & Static Electricity
Electric charge is a property that causes subatomic particles such as protons and electrons to attract or repel each other.
Protons have a positive charge.
Electrons have a negative charge.
Like charges repel
Opposite charges attract

3. Names of charges are arbitrary
Positive Charge (+) - defined as the charge on glass after it is rubbed with silk
Negative Charge (-) – Defined as the charge on rubber or amber after it is rubber with fur
Pith ball demos

5. An excess or shortage of electrons produces a charge
In an atom, a cloud of negatively charged electrons surrounds the positively charged nucleus. The atom is neutral because it has equal numbers of positive and negative charges.
If an atom gains electrons, it becomes a negatively charged ion.
If an atom loses electrons, it becomes a positively charged ion.
An excess or shortage of electrons produces a charge

6. Charge The SI unit of electric charge is the coulomb (C).
It takes about 6.24 × 1018 electrons to produce a single coulomb.
A lightning bolt is about 10 to 20 coulombs of charge, and a camera flash is about coulombs.

7. Electric Forces Like charges repel Opposite charges attract
The force of attraction/repulsion between electrically charge objects is electric force

8. Electric Fields
The effect an electric charge has on other charges in the space around it is the charge’s electric field.
Strength of the field depends on amount of charge producing it and on the distance from the charge

9. Static Electricity
Study of the behavior of electric charges, including how charges are transferred between objects
Several ways charge can build up or move
Friction
Contact
Induction
Law of Conservation of Charge
Total charge in an isolated system is constant

10. Charging by Friction
Rubbing a balloon on your hair causes charging by friction.
Electrons move from your hair to the balloon because atoms in rubber have a greater attraction for electrons than atoms in hair.
The balloon picks up a net negative charge.
Your hair loses electrons and becomes positively charged.

11. Charging by Contact
A Van de Graaff generator builds a charge on a metal sphere. Touching the sphere transfers charge by contact.
The sphere is still charged, but its net charge is reduced.
Sphere is supplied a continuous flow of negative charge, which is then given to you…. And since the negative charges in your hair will repel each other your hair stands up on end

12. Charging by induction
Walking on a carpet builds a negative charge on your body. The negative charge in your hand repels electrons in a metal doorknob.
The doorknob is still neutral, but charge has moved within it This is induction, a transfer of charge without contact between materials.
Static Discharge – The shock you feel. Occurs when a pathway through which charges can move forms suddenly

13. Lightning
Lightning animation

14. 20.2 – Electric Current and Ohm’s Law

15. Electric Current Continuous flow of electric charge
Unit – Ampere, or Amp (A) which equal 1 Coulomb per sec
By convention, Current is the rate at which + charge flows in a circuit, in reality it is the negatively charged electrons that actually move

16. Conductors & Insulators
Electrical conductor
A material through which charge can flow easily
Electrons in atoms are not tightly bound to atom
Copper, Silver
Electrical insulator
Material through which charge cannot flow easily
Do not have free electrons (held more tightly to the nucleus)
Wood, Plastic, Rubber, and Air

17. Resistance Opposition to flow of charges in a material Unit is the Ohm
A materials thickness, length and temperature affect its resistance
As temp goes up, R goes up
As thickness decreases, R goes up
As length increases, R goes up

18. Voltage
In order for charge to flow in a conducting wire, the wire must be connected in a complete loop that includes a source of electrical energy.
Charges flow from a higher potential energy to a lower potential energy
PE depends on its position in an electric field.
Potential Difference is the difference in electrical potential energy between two places in an electric field.
Measured in Joules per Coulomb, or Volts. B/c of this potential difference is also called voltage
Voltage sources do work to separate charges, b/c of this they have a potential difference and can do work

19. Voltage
A pump lifts water to the top of the fountain, increasing the gravitational potential energy of the water. A voltage source increases the electrical potential energy of electric charges.

20. V = IR Ohm’s Law Voltage = Current x Resistance
Increasing the voltage increases the current, keeping the same voltage and increasing the resistance decreases the current

21. 20.3 – electric Circuits
Electric Circuit – A complete path through which charge can flow
Circuit Diagrams- use symbols to identify different components in a circuit
Open Circuit - Circuit is not complete -- Switch is “Off”, so no current can flow
The direction of Current is defined as the direction in which positive charges would flow….. Electrons in a wire flow opposite direction.

22. Series Circuit
Only one path for current to follow

23. Parallel Circuit
An electric circuit for two or more paths through which charges can flow
If one element stops working in a parallel circuit the others can still operate

24. Key IDeas
Differences between el conductors & insulators is explained by how freely the electrons flow through the material due to how firmly the electrons are held to the nucleus
Origin, motion and energy of electrons in circuits
Role of batteries as energy sources and resistors as energy dissipaters in circuits
By convention Current is the rate at which + charge flows in a circuit, in reality it is the negatively charged electrons that actually move
Current is measured in Amperes (1 Coulomb of charge per sec)
In a circuit the power source supplies the electrons already in a circuit electric potential energy by doing work to separate opp charges… this separation is what causes the electrons to flow
Resistors oppose the rate of charge flow in a circuit
Conceptual understanding of potential difference
Potential difference (voltage) is a measure of PE in Joules supplied to each coulomb of charge.
Potential difference is a property of the energy source and does not depend on devices in the circuit
Current and resistance and the relationship between them
Current increases as potential difference increases, or as resistance decreases