Static Electricity Static Electricity accumulation of excess electric charges on an obj pg 194 Protons electrical charge Electrons electrical charge Example of electron transfer ID: 784353
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Slide1
Electricity 7-1, 7-2
Electric Charge and Electric Current
Slide2Static Electricity
Static Electricity-
accumulation of excess electric charges on an obj. pg. 194
Protons = + electrical charge
Electrons= - electrical charge
Example of electron transfer:
Walk on carpet, the electrons are transferred from carpet to your shoes
Shoes have a more - charge and carpet is more + = static electricity
Slide3Conservation of Charge
When an object becomes charged the charge is neither created nor destroyed (Law of Conservation of Charge)
Electrons move from one object to another
Slide4Opposites Attract
**Opposite charges attract- like charges repel
(+) charges are attracted to (–) charges.
Slide5Electric Field
Surrounds every electric charge- force that causes electrons to move
Slide6Conductors and Insulators
Conductors- material in which electrons move freely ex. Metal, skin
Insulators- material that doesn’t allow electrons to flow smoothly. Ex. Plastics, wood, glass, rubber
Slide7Transfer of Charge
Charging by contact-
process of transferring charge by touching or rubbing (rubbing balloon on head)
Fig. 7 pg. 198-
Charging by induction-
the rearrangement of electrons on a neutral object (static cling)
Lightning-
large amount of static discharge
Fig. 8
Slide8Detecting Electric Charge
Electroscope Fig. 10 pg. 199
No charge- leaves hang straight down
Object is charged- leaves repel (move apart)
Slide9Electric Current 7-2 Notes 813
I. Voltage Difference- the push that causes charges to move and is measured in
volts (V).
(
move from areas of high voltage to low voltage
)
An object may lose voltage as it flows through a circuit.
II. Circuit- a
CLOSED
, conducting path (must be closed to have a circuit)
III. Electric Current-
a flow of charges through a wire or any conductor.
Current is measured in
Amperes (A)
Current is the flow of electrons.
Most wall sockets are 120 V in our homes.
Slide10Batteries
Batteries keep current flowing in a circuit.
Dry Cell (D, C batteries)- electrons flow from positive to negative terminal.
Positive terminal is where carbon rod is located.
Wet Cell- car battery is a wet cell battery.
Slide11Resistance
The tendency for a material to oppose the flow of electrons, changing electrical energy into thermal energy and light.
All materials have SOME electrical resistance.
Resistance is
measured in ohms
pg. 205
Metals (conductors) have low resistance.
Insulators have high resistance.
Resistance as temperature
Thick v. Thin wire= Thin wire has a greater resistance.
Slide12Ohm’s Law
Increasing resistance causes the current to decrease. Increasing the pressure causes the current to increase.
Ohm’s Law- the current in a circuit equals the voltage difference divided by the resistance.
I = V / R current = volts/ resistance
or
V = IR volts= current x resistance
Practice Problems from Ohm’s Law
1. What is the voltage difference across a 70 ohm
resistor
if a .9A current is flowing through it?
2. A current of .24 A flows through a wire. What’s
the
resistance if the voltage is 70V?