Understanding Static Electricity

Static Electricity

• Electrostatic is the study of static electric charges
• Electric charges can be positive (+) or negative (-).
  • Like charges repel each other.
  • Unlike charges attract each other.
• The force between electric charges weakens as the separation increases.

Charges, Atoms, and Electrons

• Atoms contain protons, neutrons, and electrons
  • Protons are in the nucleus of the atom and have a charge of +1
  • Neutrons are in the nucleus and have no charge.
  • Electrons orbit the nucleus and have a charge of -1.
• Normally, atoms have an equal number of protons and orbiting electrons, making them neutral
  • Gaining extra electrons results in a negative charge.
  • Losing electrons results in a positive charge.
  • Atoms that gain or lose electrons become ions.

Conductors

• Conductors allow electricity to flow through them easily
• Examples of conductors include graphite, copper, tin, and gold.
• In conductors, outer electrons are loosely bound and move freely

Insulators

• Insulators do not allow electricity to flow through them easily
• Examples of insulators include plastic, rubber, glass, and wood.
• In insulators, atoms hold tightly to their electrons

Charging Process

• Static electric charges can be acquired by rubbing, which is for insulators
• Static electric chares can be acquired by induction, which is for conductors

Charging by Rubbing (Friction process)

• Rubbing separates charge by transferring electrons from one object to another.
• When an uncharged glass rod is rubbed with an uncharged cloth, electrons from the rod move to the cloth
  • The rod loses electrons and becomes positively charged.
  • The cloth gains electrons and becomes negatively charged.

Charging by Induction

• Charged objects exert forces on other charged objects without contact.
  • Similar charges repel each other.
  • Opposite charges attract each other.

Gold Leaf Electroscope

• The metal plate at the top is connected to a metal rod inside, with a small piece of 'gold leaf' attached.
• If an electrically charged object is brought close to the top plate, the gold leaf moves

Forces Between Charged and Uncharged Objects

• Attraction between charged and uncharged occurs because of electrostatic induction

Dangers of Static Electricity

• Lightning
• Refueling
• Operating threats
• Computers

Uses of Static Electricity

• Flue-ash precipitation
• Photocopiers
• Inkjet printers
• Electrostatic paint spraying

Electric Fields

• The region where an electric charge experiences a force due to other charges
• The electric field is a region where electric forces act

Electric Current and Formula

• Electric current (I) is the rate of flow of electric charge
• I = Q/t, where Q is electric charge and t is time taken
• Q = ne
• The unit of current is the ampere (A)
  • (1 C/s = 1 A)
• Use an ammeter to measure current
  • The ammeter is connected in series with the part of the circuit

Conventional Current

• Before electrons were discovered, current was thought to be positive charges moving from positive to negative in a battery
• Electrons flow in the opposite direction of the conventional current
• Effects of electric current:
  • Heating and lighting effect (electric iron, immersion heater, stove, lamp, bulb) because the wire (filament) is heated by the current
  • Magnetic effect (electric bell, telephone, electric motor) caused by the magnetic field from current carrying wire
  • Chemical effect (charging batteries, electroplating, purifying metals) because bubbles of gas are given off at the wires in the acid due to the chemical action of the current

Circuit Diagrams

• Current needs a complete path (a circuit) of conductors to flow

Series Circuits

• Circuits with no branches or junctions that have only one path for current
• In a series circuit with bulbs:
  • One switch can turn all bulbs on and off.
  • If one bulb breaks, all bulbs stop working.
  • Energy is shared between bulbs, so more bulbs make them less bright.
• Current is consistent in all parts of the circuit

Parallel Circuits

• Circuits with branches or junctions where current can follow more than one path
• In parallel bulb circuits:
  • Switches can be placed in different parts of circuit and only switch on that part
  • If a bulb breaks, only the bulbs don't he same branch will be affected.
  • Each branch gets a separate voltage, so more bulbs have the same brightness
• Currents not consistent in all parts, current entering and leaving a current are equal

Direct Current (d.c.)

• Electrons flow in one direction only

Alternating Current (a.c.)

• The direction of flow of electrons reverses regularly
• Batteries give d.c. and generators can produce either d.c. or a.c.

Frequency of a.c.

• Frequency of a.c. is measured by number of complete alternations/cycles in one second
• the unit is the hertz (Hz)
  • The mains supply is 50 Hz in the UK

Potential Difference (Voltage)

• Defined as the energy converted from electrical to other forms when a unit positive charge passes between two points in a circuit
• V=E/Q, where V is potential difference (voltage), E is energy transferred, Q is electric charge

E=Q x V

• Unit of p.d is the volt (V)
  • ( 1 J/C = 1 V)
• Voltmeter measures voltage or p.d. and connected in parallel with the circuit

Electromotive Force (e.m.f.)

• Energy converted from non-electrical to electrical form when a unit positive charge passes
• Measures energy supplied by source in driving charge around a complete circuit E.m.f = E/Q = W/Q
  • E is the energy supplied, Q is the charge
• Unit is the volt (V)
  • 1 J/C = 1 V Sources are
    • Batteries
    • Generators

Voltages in Series

• Voltage is achieved when cells are joined in series (+ of one to – of next)
  • Total = 2V + 2V + 2V = 6V
• Cells in opposition the voltage is 0.

Voltages in Parallel

• If cells are connected in parallel, voltage at terminals is still but arrangement behaves like bigger cell that will lasts longer.

Voltage in Circuits

• Voltage at the terminals of a battery equals the sum of the voltages across the devices in the external circuit from one battery terminal to the other
• V = V1 + V2 + V3
• Voltages across devices in parallel in circuit are equal
  • V = V1 = V2

Resistance

• The opposition of a conductor to current
• R= V/I (V= Voltage and I = Current)
• Unit Ohm (Ω)
  • A good conductor has good resistance and the opposite is true for a bad conductor
  • R = pL/A
    • R: the resistance
    • p: a constant for a given material (resistivity).
    • L: the length of the wire
    • A: cross-sectional area

Resistivity

• Numerically equal to the resistance of a 1 m length of material with cross sectional area 1m^2
• Unit p is ohm-metre Ωm
  • p= RA/L

Ohm's Law

• Current in a metallic conductor is directly proportional to the voltage across its ends if temperature and conditions are constant
  • V = IR
    • Metallic conductors I–V graphs that are a straight line through the origin called Ohmic Linear Conductor and since I V=Constant
• Resistors intended to have resistance that has two types

Fixed Resistors

• Resistors whose resistance does not change with the change in voltage or temperature
• An ideal fixed resistor constant resistance

Variable Resistors

• A resistor of the electric resistance value can be adjusted

Resistors In Series

• Resistors are same current flows and the total voltage V across all is same
• R= R1 + R2 + R3
  • Voltage gets divided but the current constant

Resistors In Parallel

• Resistors are in parallel voltage the ends of each same and the total current I branch circuit.
• 1/R = 1/R1 + 1/R2 + 1/R3, Voltage stays consistent but current changes.

Light Dependent Resistors

• Change intensity to resistance

Potential Divider for Monitoring Temperatures

• thermistors

Electric Power

• Rate of energy transfer or amount of energy transferred per second

Formula

• Power = current x voltage or P= I x V
• P = l² x R
• P = V² /R
• Power of a device depend on voltage (potential difference) and current.
  • transfer lots of energy have power rating in Kilowatts (kW) and Megawatts (MW), joules per second or Watts (W) - 1 kW = 1 x 10³W - 1MW = 1 x 10⁶W

Electrical Energy

• Energy is equal to the amount multiplied by the amount of seconds
  • E=P x t.
  • E = l x V x T ,
  • E = l² x R x T
  • E = V²t/ R.
    • Electrical unit - Kilowatt per hour
    • Kilowatt = KW = 1000js x amount of seconds = 36000,00 is equivalent to 3.6 MJ . Electricity and heaters.

Fuses

• Protects a circuit

Facts

• Wire or material point is made copper breaks circuit.
• Fuse capacity of wire not to be exceeded switch before replacing recommend appliance
• Fuse sizes

House Circuits

• Underground cables containing two wires on a circuit live and neutral
• Earth, neutral, Earth.

Facts

• Circuits live wire so no appliance switches in fault electric wires

Safety

• Earth Wire cases
  • Low for circuit.
  • Is to blow is to switch safety.
  • Button

Double insulation

• plastic

Joulemeters

• Electricity charges joule and kilowatt per hour kWh and Dangers of
  • Conditions increase shocks
  • Precautions correct fuse
  • Appliances heat

Electronics systems

• increasing
  • Sensor
  • Process
  • Output Transducer

Transducer

• non into vice
• LDR Lightherm

Output Trasducer

• Energy Transducer diodes

Semiconductor Diodes

• Current that one direct
• Negative.
• is as a that 1, Terminal
• the Terminal resistance is.

Forward

• biased that is

Is-Reverse

• biased