Transcript Charge & Electricity

Unit 6 – Lecture 1
Review
 3 types of subatomic particles
 protons: + charged
 neutrons: non-charged
 electrons: - charge
 Equal p+ & e- = neutral
atom or compound
 Objects with no net charge
are called neutral
Charge
 Charge – a point source of electrical force
 two types – positive and negative
 opposite charges attract
 like charges repel
 most objects are neutral
Conservation of Charge
 Law of Conservation of Charge
 charges are neither created nor destroyed, they can
only be transferred from one object to another
Review
 “Sea of Electrons” – elements in a metallic bond do not
hold their electrons tightly, but share them between all
atoms
Static Charge
 static electricity –
the accumulation of excess
electric [negative]
charge on an object
 static = not in
physical motion
 “static cling” –
objects that are
oppositely charged
“stick” together
Static Charge
 static electricity – the accumulation of excess electric
[negative] charge on an object
 electrons are being transferred
from the carpet to your shoe
 electrical discharge – sudden
and momentary electric
current between two objects
Static Charge
 Lightening is a form of static discharge
 static charges are formed when the particles inside
the storm cloud rub against each other [because of
convection], separating charges.
Electric Field
 area around a charged object which exerts forces on
other electric charges
Review
 Conductor
 a material through which electrons can move easily
 best are metals [sea of electrons]
Review
 Insulator
 a material through which electrons are not able to
move easily
 plastic, wood, rubber, glass…etc
Charging Objects
 Charge by Contact
 transfer of charge by direct touch or rubbing
 static cling
Charging Objects
 Charge by Induction
 rearrangement of electrons in a neutral object
because of a charge from a nearby object
Electricity
 Electric Current [I]– the net movement of electric
charges in a single direction
 ex: spark between you and doorknob
 measured in Amperes [A]
 1 A = 6,250 million billion electrons per second
passing a single point
Electricity
 Volt (V) – unit of the PE of an electrical charge
 electricity flows from that of higher voltage to lower
voltage
Resistance
 Resistance [R] – a material’s
opposition to the flow of
current
 measured in Ohms (Ω)
 resistance will turn
electrical E
into thermal E and light
Resistance
 Resistance [R] – a material’s
opposition to the flow of
current
 conductor – less resistance
 insulator – more resistance
Resistance
 Increase resistance with…
 increase temperature
 increase length
 decrease thickness
Resistance
 Decrease resistance with…
 more, smaller batteries
 shorter, thicker wire
 more conductive metal
Electricity
 Ohm’s Law:
 Current = Voltage / Resistance
 I=V/R
 Voltage = Current * Resistance
V
 V=I*R
 Resistance = Voltage / Current
 R=V/I
I
R
Electricity
 Power (W) is measured in Watts
 Power = Voltage * Current
 Watts = Volts * Amps
P=V*I
P
V
I
Practice
 The current in a clothes dryer is 15 A when plugged
into a 240 V outlet. How much electrical power does
the clothes dryer use?
 3,600 watts OR 3.6 kilowatts
 Calculate the voltage difference in a circuit with a
resistance of 50 Ω if the current of the circuit is 0.7 A.
 35 volts
Electricity
 Electrical Energy is measured in kilowatt hours [kWh]
 Electrical Energy = Electric Power * time
E=P*t
 A microwave oven with a power
rating of 1,200 W is being used
for 0.25 h. How much electrical energy is being used by
the microwave?
 0.30 kWh
E
P
t
Homework
 For ALL problems, show ALL work:
1. Write Equation
2. Plug In Numbers
3. THEN Solve for Answer
ALL PROBLEMS MUST
HAVE THESE THREE STEPS
Homework
 p 199 #s 6-7
 p 212 #s 1-4
 p 205 #s 6-7
 p 213 #s 6-8
 p 211 #s 1-4