Download Electricity

Electricity
The flow of charges
Atoms
 Made up of:
 Nucleus: Protons
and neutrons
 Electrons:
negative charge
orbit nucleus
Current
 Flow of electrons
 Measured in Amperes (Amps)
Electrons passing per second
Circuit
 Must have complete, unbroken
path for current to flow
 3 Parts:
1. Load: device run by electricity
2. Wires: path for electron flow
3. Source: moves the electrons
through the wire
 Battery, generator, wall socket (power
plant)
A break in the circuit stops electricity
from flowing
Conductors
 Materials allowing electrons to flow
 Examples:
 metals: electrons loosely held, move easily
 Copper is one of the best
Insulators
 Do not allow electricity to flow
 Examples: rubber, plastic
 Electrons held tightly, will not move easily
Voltage
 Measures the force “pushing”
electrons
 Volt (v) as unit
 Higher voltage is higher potential to push
electrons through circuit
 Water dam
Lower Potential energy =Low
voltage
Higher Potential
energy=high voltage
Resistance
 Force working against (“resisting”)
the flow of electrons
 Measured in Ohms (Ω)
 All parts of circuit “slows the flow”
Ohm’s Law
 Tells how current, voltage, resistance
are related
 Current =
I=
voltage
resistance
V
R
Practice Ohm’s Law
 A 9 volt battery is used to light 3 bulbs with a
resistance of 0.5 Ω each. Wires and a switch add
another 3 ohms of resistance. How much current
(amps) is flowing through the circuit?
 Plan
 What information is given?
 9 volts, 3 bulbs x 0.5 ohms = 1.5 ohms plus 3 ohms for
total of 4.5 ohms.
 What formula do I use?
 I=v/r
 I = 9 v / 4.5 Ω
 Solve
 I = 2 amps
 Check:Does it make sense?
 The current is less than the voltage because the
resistance is reducing the flow
Circuits and Current
Direction
Series Circuit
 Only one path for
electricity to flow
 What happens if
one bulb goes out?
 Will the bulbs be
dimmer or brighter
than a parallel?
Load (bulb)
Switch
Parallel circuit
 More than one path
for electricity to
flow
 Each load on
separate circuit
 What happens if
one bulb goes out?
 Compare
series/parallel to
water supply
Current Direction
 Current always flows in one direction:
From negative to positive
AC vs. DC
Direct Current
DC
 Charges always flow in same
direction, from negative terminal to
positive terminal
 Battery (cells)
Cells
and
Batteries
9
Volt
Battery
plastic seal
anode collector
plastic sleeve
anode
steel jacket
 Convert chemical
Case sleeve
energy to electrical
energy
Cell straps
 Potato clock
cathode
Electron acceptor
Negative terminal
cathode collector
electrolyte
Positive terminal
Electron donor
Other sources of DC
 Thermocouple: convert heat to
electricity
 Solar cells: convert solar energy to
electricity
Alternating Current
AC
 Charges flow from negative to
positive but switch directions back
and forth (alternate)
 House current
Producing AC current
 Induction: Coil of wire and magnet produce
electricity
 It’s electro-magnetism!
 Generator: converts mechanical energy
to electrical energy
 Motor: converts electrical energy to
mechanical energy
Electromagnetism
 Magnetism and Electricity are closely
related
 Electric current causes magnetic
fields
 Cell phones, television, light
 Magnets can cause an electric current
to flow
 Generators
Power
 Measures how fast energy is
transferred from one form to another
 Measured in Watts
 Power = voltage x current
 P= V I
 A 100 watt light bulb changes or uses
electrical energy to light energy twice as
fast as a 50 watt bulb
 Brainpop on current