Electricity

Charges

• Atoms contain particles called protons, neutrons, and electrons.

• Protons (+)• Electrons (-)• Neutrons (0)

Charges & Forces

• Electric Charge – a property that causes subatomic particles to attract (unlike charges) or repel each other (like charges)

• Electric Forces – the force of attraction or repulsion between electrically charged objects (depends on distance)

Charging Objects

• Rubbing two materials together can result in a transfer of electrons.

• Then one material is left with a positive charge and the other with an equal number of negative charges.

• The process of transferring charge by touching or rubbing is called charging by contact.

Charging Objects

• Conduction – the contact of a charged object to a neutral object.

• Friction – when two objects are rubbed together, one becoming negatively charged and the other becomes positively charged.

• Induction - A method used to charge an object without actually touching the object to any other charged object.

Charging Objects

• Law of Conservation of Charge – charge cannot be created or destroyed only transferred.

• The accumulation of excess electric charge on an object is called static electricity.

Conductors

• A material in which electrons are able to move easily is a conductor.

• Metals are the best electrical conductors because they have freely moving electrons.

Insulators

• A material in which electrons are not able to move easily is an insulator.

• Plastic, rubber, and glass are good insulators because they hold onto their electrons tightly.

Electricity

• Electric Current – the continuous flow of electric charge (Measured in Amps (A))

• Electrons in metals are in constant motion in all directions.

• When an electric current flows in the wire, electrons continue their random movement, but they also drift in the direction that the current flows.

Electricity

• An electric field surrounds every electric charge and exerts the force that causes other electric charges to be attracted or repelled.

• Any charge that is placed in an electric field will be pushed or pulled by the field.

Voltage

• Voltage • causes current to flow through an electrical

circuit • measured in volts - V• A Voltage Source (battery or generator) is

required to maintain the electrical potential in a circuit.

Resistance

• Resistance• opposition the flow of electrons• measured in ohms ()

Copper - low resistance

Tungsten - high resistance

Resistance

• Resistance depends on the conductor (wire)• thickness - less resistance in thicker wires• temp - less resistance at low temps• length - less resistance in shorter wires

Circuit

• A circuit is a closed path through which electrons can flow

Circuits

Scientist usually draw electric circuits using symbols

Circuits

A - battery C - light bulbB - switch D - resistor

Circuits

• ipad activity… making circuits!!!

Circuits

• A closed (on) switch means that the circuit through the switch is connected, this is called a closed circuit.

• A broken wire or an off switch both leave gaps in a circuit this is called an open circuit.

Circuits

• Series Circuit• current travels in a single path• one break stops the flow of current• current is the same throughout circuit • lights are equal brightness• each device receives a fraction of the total

voltage • get dimmer as lights are added

Circuits

• Parallel Circuits• current travels in multiple paths• one break doesn’t stop flow• current varies in different branches• takes path of least resistance• “bigger” light would be dimmer• each device receives the total voltage• no change when lights are added

Circuits

• Safety Features:• fuse - metal melts, breaking circuit• circuit breaker - bimetallic strip bends

when hot, breaking circuit

Voltage

Ohm’s Law• V – Volts (V)• I – Current (amps, A)• R – Ohms ()• If voltage remains constant: current &

resistance are inversely proportional

V = IR

IV

R÷

Voltage

Practice Ohm’s Law1.What is the voltage if the resistance is 3 ohms

and the current is 3 amps?V = IRR = 3 ohmsI = 3 ampsV = 9 volts

Voltage

2. A light bulb with a resistance of 160 ohms is plugged into a 120-V outlet. What is the current flowing through the bulb?

V = 120 voltsR = 160 ohmsI = V/RI = 0.75 A

Voltage

3. What voltage produces a current of 200 amps with a resistance of 20 ohms?

4. What is the resistance of a lamp operating at 100 volts and using 0.5 amps of current?

5. How much current is used when a 10 ohm heater is connected to a 120 volt source?

6. What is the voltage if the resistance is 6 ohms and the current is 5 amps?

Power

• Electrical Power – rate at which electrical energy is converted to another form of energy.

• P = power (W)• I = Current (A)• V = potential difference (V)

P = IV

IP

V÷

Power

Electrical Power Practice1.A calculator has a 0.01-A current flowing through it. It operates with a potential difference of 9 V. How much power does it use?I = 0.01 AV = 9VP = 0.09 W

Power

2. How much power does a 27 A clothes dryer use if it is connected to a 240 V electrical source?

3. A power tool used about 12 amperes of current and has a power rating of 1440 watts. What voltage does the tool require?

4. A stereo receiver used a current of 2.2 amps from a 120 volt line. What is its power?

Vocabulary

1. Electric Charge2. Electric Force3. Contact4. Conduction5. Friction6. Induction7. Law of Conservation of

Charge8. Static Electricity9. Conductor (Example)10. Insulator (Example)

11. Electric Current12. Electric Field13. Voltage14. Resistance 15. Circuit16. Open Circuit17. Closed Circuit18. Series Circuit19. Parallel Circuit20. Power