## Monday, March 17, 2014

### ELECTRICITY - CHEAT SHEET

ELECTRICAL EQUATIONS
Voltage = Volts                        Current = Amps                       Resistance = Ohms
Voltage = Current  x Resistance
Current = Voltage / Resistance
Resistance = Voltage / Current
Watts = Joules/second
Volts * Amps = Watts
Electric Power = rate @ which energy is transformed from one form to another
Power = Watts
1 Kilowatt is 1,000 watts

• 1 watt is equal to 0.001 kilowatt.
Watts * Time = Joules or total energy consumed

Increasing Voltage increase the current
Increasing the Resistance will decrease the current
Voltage & current are directly proportional
Current & Resistance are inversely proportional

HOW STATIC ELECTRICITY IS PRODUCED
1. When two different objects that are insulators (such as a plastic rod and silk cloth) are rubbed together, electrons move from one object to another.
2. One object becomes negatively-charged, and the other object becomes positively-charged.
3. The more rubbing, the more electrons are transferred, and the larger is the charge built up.
4. Unlike charges (positive and negative) attract each other.

·   Current Electricity or electric current is the movement of negatively-charged electrons through wires or objects with metals, carbon or water.
·   Conductors are substances that allow electrons to travel easily through them (e.g. metals, carbon and water).
·   Insulators or non-conductors are substances that do not allow electrons to travel easily through them (e.g. plastic and wood).
·   Resistors are substances that are poor conductors. They convert much of the energy of moving electrons into light, heat or sound energy in light bulbs and stereos.
·
A simple cell consists of 2 different conductors (electrodes) partly covered by an acidic or ionic solution (electrolyte solution).

·     Different combinations of electrodes produce different

·      voltages.
·   For example, electrodes of zinc
and copper produce 1.1 volts, whereas electrodes of
aluminum and carbon produce
2.4 volts.
·   Rechargeable Cells (e.g. lead-acid cells) are cells that can be recharged when they go 'flat' by reversing the chemical reaction.
·   Electrical power is the amount of electrical energy used    by an appliance every second. It is measured in Watts.
·   When paying for electricity, we use the unit kiloWatt-hour (kWh). One kWh is the energy used by a 1000 watt appliance switched on for one hour.
·   Example:
Q. A 200 watt TV set is used for 6 hours. How many kilowatt-hours of electricity were used?
 A. Number of kWh = kilowatts × number of rating hours = (200 W⁄1000) × 6 h = 1.2 kWh
SERIES CIRCUIT

• Series Circuit - a circuit where the components are connected one after the other into a 'circle'.
• Ammeter - This device is used to measure current in amperes (A). It must be wired into the circuit in series.
• Disadvantages of Series Circuits - As more light bulbs are connected in series, the brightness of all bulbs decreases.
PARALLEL CIRCUITS
• Parallel Circuits are combined circuits where components such as light bulbs glow equally brightly.
• This form of wiring is used in household circuits.
• Voltmeter - a device for measuring voltage (or
• potential difference), and must be wired into the
• circuit in parallel
• Short Circuit - A short circuit occurs when a
• conducting object such as a screwdriver lies
• between two circuits. The electrons take the
• 'shorter' circuit through the screwdriver.

HOUSEHOLD CIRCUITS
• Fuse - The fuse is a thin wire with a low melting point near the power source to a house. It heats up readily and melts to disconnect the circuit to the house when excessive current flows. The fuse may 'blow' in the event of a power surge to the house, or due to a faulty electrical appliance in the house. A circuit-breaker serves a similar purpose.
• Ground/Earth Wire - All households must have a connection between the household wiring and the earth. This is to carry away any extra surge of electricity that may occur during lightning storms or as a result of a faulty appliance.
• Electric Plug - Most electric plugs have 3 connections - Active or 'Live' (brown), Neutral (blue) and Earth (green/yellow). However, appliances with plastic exteriors do not always have the third earth connection.
• DC (Direct Current) - Direct current is a current in which electrons continually flow in the one direction. It is produced by batteries.
• AC (Alternating Current) - Alternating current is a current of electrons in which the direction of movement of electrons is continually changing. It is the type of current in household and industrial circuits.
3 WAYS OF GENERATING ELECTRICITY
1. Using Chemical Reactions in Electric Cells - The chemical energy of the electric cell is converted to electrical energy.
2. Using Light in Solar Cells - Solar or photo voltaic cells are made of elements such as silicon which readily free electrons when exposed to sunlight energy. The light energy is converted into electrical energy.
3. Using Magnets - Moving a magnet through a coil of wire causes the electrons to flow through the wire. This is called the electromagnetic effect or induction. Moving the magnet in the opposite direction causes the current to reverse. To increase the current, one can increase the strength of the magnet, the number of turns in the coil, or the speed of movement of the magnet.
OHM'S LAW

• Voltage or Potential Difference (volts, V) = Current (amperes, A) × Resistance (ohms, Ω)
 I = V R
V = I × R
 R = V I

ELECTRICITY SYMBOLS

The best real-life example of direct current is a battery.
Batteries have positive (+) and negative (-) terminals. If you take a wire and connect the positive and negative terminals on a battery, the electrons in the wires will begin to flow to produce a current. You can prove that the current is flowing if you connect a small light to the circuit. The light will begin to glow as the electrons pass through the filaments.   Everything that uses batteries runs on DC power.

Electric wiring in your house is AC power and it is completely different than DC.

The electricity produced by a generator travels along cables to a transformer, which changes electricity from low voltage to high voltage. Electricity can be moved long distances more efficiently using high voltage. Transmission lines are used to carry the electricity to a substation. Substations have transformers that change the high voltage electricity into lower voltage electricity. From the substation, distribution lines carry the electricity to homes, offices and factories, which require low voltage electricity.

Household electricity is around 240 volts in
some countries and 110v. in others. Such
high voltages may give you deadly shocks,
so appliances are protected by "fuses".
Fuses
, contain thin pieces of wire that melt
and cut off current if it is too large. Electricity
is carried to the different parts of the house
by parallel circuits. The parallel circuits
contain 2 wires called the "live and neutral
wires
". Some countries use "Earth wire",
which is a safety device that provides a path
to the ground which electric current can
escape

Electrical Power
• Electrical power is the amount of electrical energy used by an appliance every second. It is measured in Watts.
• When paying for electricity, we use the unit kiloWatt-hour (kWh). One kWh is the energy used by a 1000 watt appliance switched on for one hour.
• Example:
Q. A 200 watt TV set is used for 6 hours. How many kilowatt-hours of electricity were used?
 A. Number of kWh = kilowatts × number of rating hours = (200 W⁄1000) × 6 h = 1.2 kWh