Download Science 9 electricity powerpoint Topic 1

Science 9 Unit D
Section 1.0
Electrical Principles & Technologies
1.1 – Static Electricity
 Static electricity is produced when two objects rub
together
 This produces a buildup of charge on the objects
being rubbed together
 http://www.youtube.com/watch?v=fT_LmwnmVNM
How Static Electricity works
The Atom
Protons have a
POSITIVE CHARGE
Electrons have a
NEGATIVE CHARGE
Electrical Charge
 Positive and negative charges on an object are due to
the ratio of protons and electrons present in an object
 Objects are negative when they have more electrons
than protons
 Objects are positive when they have more protons than
electrons
 Objects are neutral when the amounts of positive and
negative charges are equal
Producing a Charge
 Charges are produced when electrons
move from one object to another
 An object that loses electrons becomes
positively charged while one that gains
electrons becomes negative
 Only the electrons move,
never the protons!
Charge Separation
 Charged objects cause charge separation
when they are brought near to neutral
objects
Electrical Discharge
 Static electricity generally does not move – it
remains stationary (or is static)
 However, a built-up static charge on an
object can be attracted to other objects and
jump to the object
 Often this creates a small spark, which is
known as an electrical discharge
Laws of Electrical Charges
 Opposite charges attract each other
 Like charges repel each other
 Neutral objects are attracted to charged
objects
Van de Graaff Generators
 A Van de Graaff Generator is used
to study electrical charges
 A rubber belt running in the
generator rubs against metal
“brushes” and creates a static
charge
 The charge is then transferred
to the metal sphere, where the
static charge builds up
Mythbusters
Van de Graaff generator
 http://www.youtube.com/watch?v=7qgM1A3pgkQ
1.2 – Current Electricity
 Static charges do not work very well for
operating electrical devices
 Electrical current is produced as charges move
in a continuous flow
 An electrical current flows until it is used up or
disconnected
 Think of it like water flowing until it is dammed
or its source drives up
Electric Eels
 http://www.youtube.com/watch?v=a3sviTa8hZw
World’s deadliest:
Six-Foot Electric Eel
Amperes
 The rate at which current flows is measured
in amperes (A)
 Called Amp for short
 Named after Andre-Marie Ampere
 Electrical current refers to the number of
electrons passing a point in a circuit per
second
How do we move electricity to its
destination?
 Answer: CONDUCTORS
Conductors are materials that electrical energy
can move easily through
Circuits
 A circuit is a path that controls the flow of
electricity
(just like pipes and taps in a water system
control the flow of water)
 In most pathways, electricity flow along
solid metal wires, but circuits can also include
gases, other fluids, etc
Parts of a Circuit
 A complete electrical circuit consists of:
LOAD: a device that converts electrical energy to
another form (ex. A lightbulb)
ENERGY SOURCE: source of electrical energy
(ex. Battery)
CONDUCTOR: pathway for electricity to flow
(ex. Wires)
Electrical Energy & Voltage
 Voltage is the measure of the amount of
electrical energy carried by each particle
 Voltage is also known as “potential difference”
 The unit for voltage is known as the Volt (V)
 Voltmeters are used to measure voltage
Measuring Voltage
 When setting up a voltmeter, the red lead must run to
the positive battery terminal, and the black lead
should run to the negative terminal
1.3 Electrical Safety
 Electricity has the ability to seriously injure or
kill
 This is because electrical current can interrupt
the function of the nervous system and
heart (both of which rely on their own electrical
current to operate)
Short Circuit
 A short circuit is an unintended pathway for
electricity
 The current bypasses part of the normal
circuit
Electrical Shock
 High voltage is more likely to cause damage than
low voltage
 However, the number of amps is much more
significant
 This is because you may only have a few high-energy
electrons flowing through you if there is a high
voltage and a low current
 However, high currents mean that lots of
electrons are flowing through your body
Current Effects
0.001 A:
0.015 A:
0.100 A:
Effects are likely not felt
Painful shock and loss of muscle control
Fatal
Protecting From Shock
 Insulators prevent the movement of electrical current
and will protect you from electrical shock
 Current does not move freely through insulators such as
wool, rubber, and air.
Electrical Safety Pointers
Plugs, Fuses & Breakers
 The third prong on electrical plugs is the ground
 This provides a route through which excess charge
can escape to the ground (instead of building up and
discharging through you!)
Plugs, Fuses & Breakers
 Both fuses and circuit breakers limit the amount of
current flowing through a circuit
 If a fuse or breaker receives too much current, the
circuit is broken and the current stops
Lightning
 The current in a lightning
strike can be as high as
30 000 A
 To avoid being hit by
lightning, avoid the
following:
- standing on hilltops or
under trees
- standing near metal objects
Lightning Rods
 Lightning rods are often added to tall building peaks
 They are connected to the ground with wires
 Any discharge from a lightning strike is conducted
harmlessly to the ground (instead of destroying the
building or its wiring)
1.4 – Cells and Batteries
 An electrochemical cell is a device that provides a steady
current that is produced by a chemical reaction
 Some people have problems with the electrical signal that
controls beating of the heart, a PACEMAKER can be surgically
inserted to send small amounts of current to keep the heart
beating normally
 Electrochemical cells come in two types:
Wet cells and dry cells
Dry Cells
 A dry cell is an
electrochemical cell that
uses chemicals in a
paste form
 The cell consists of two
different metals and
an electrolyte
 http://www.youtube.co
m/watch?v=KkRwuM4S
8BQ
Dry Cells - Terms
 An Electrolyte is a paste or liquid that conducts
electricity
 An Ion is an atom or group of atoms that has come
electrically charge through the loss or gain of electrons
 An Electrode is a metal that the electrolyte reacts with
Wet Cells
 A wet cell uses an aqueous
solution as the electrolyte
 Wet cells are less common
than dry cells
Why?
 They are more expensive,
not as reliable and can leak
Chemical Reactions &
Electrochemical Cells
 In a wet or dry cell, the electrolyte reacts with the two
metals
 One metal loses electrons and becomes positively charged
 The electrons are passed through the solution and are deposited
on the other metal, which becomes negatively charged
 When connected to a circuit, the electrons leave the negative
electrode and move through the circuit to the positive electrode
Rechargeable Cells
 Some dry and wet cells are primary cells
(they cannot be recharged)
 Secondary cells (which are rechargeable) can regain stored
charge if an electrical current is run “backwards”
through the cell
 These cells use chemical reactions that can be relatively easily
reversed
Batteries
 A battery is a collection of cells connected together
 “AA”, “AAA”, “C” and “D” type cells are not batteries –
they are single electrochemical cells
 Larger batteries such as 9-V and 12-V batteries are true
batteries
Volta
 Made the first practical battery
 He piled many copper and zinc discs on top of each other,
separating them with electrolyte-soaked paper discs
Electrolysis
 Electrolysis is a technique that is used to break free
atoms from compounds
 This is done by running a current through the substance
 For instance, electrolysis can be used to produce oxygen
and hydrogen from water
 Or separate pure metals from
molten compounds
Electrochemistry
 Is the study of chemical reactions involving electricity
Electroplating
Electroplating
 A thin layer of metal can be plated onto a cheaper
metal using electricity
 The item to be plated is immersed in an electrolyte
along with an electrode that consists of the metal that will be
used for plating
 Electricity flows from the plating metal to the
object being plated, and as a result the metal moves
across the solution and builds up on the surface of the object
being plated
Other Applications of Electrochemistry
 Anodizing – aluminum is coated with a layer of aluminum
oxide, which is much harder than regular aluminum
 Electrorefining – impurities are removed from impure metals
by placing the metal in an acid and running a current through it