Electricity

• All matter is made up of atoms

  Atoms is neutral contains + = -, particles:

  Protons (+)

  Neutrons (no charge)

  Electrons (-)
• Neuclons can not move, electron is the one that can move to

  transfer its kinetic energy into electrical energy.
• The law of electric charges states that like charges repel, and opposite charges attract.
• Atom that has less electrons called positive ion, atom that has less protons called negative ion.
• Object with less electrons called positively charged object , object

  with more electrons is called negatively charged object.
• The attraction and repulsion are because of electric force.It is shown by magnetic field from+ to -.

  Stronger force=denser electric field line and bigger electric field area.
• The size of the electric force depends on 2 things:

  1. The amount of charge (the greater the charge, the greater the force)
  2. The distance between charges (the further the distance, the less the force)
• Electricity is a flow of energy which is transferred by vibration and movement of electrons.
• The electrons are transmitted from negative plates into positive plates in batteries.
• Electrical current is the movement of 1 Coulomb of charge in one

  second.

  I = q/ t =charge (C) / time (s)

  Unit = Ampere (A) or milliAmpere (mA). Magnitude 1e=1p=1.6x10-19 C
• The difference of energy per unit of charge to share from

  one point to another is called potential difference or

  voltage.

  V = E/q

  V=voltage(volt), E=energy(J),

  q=charge(Coulomb)
• Resistance is the obstacle of the electrical energy flow in circuit.’Any

  material has resistance. Unit : Ohm or Ω.Symbol in cirtuit:

  ρ = resistivity in

  Ohm-meters

  R=pl/A

  Good conductors (low ρ): Copper, Gold

  Good insulators (high ρ): Glass, Paper

  Apparently resistivity is the inverse of conductivity

  ρ = 1/ conductivity
• The relation shows that voltage

  is directly proportional to

  current which also means the

  resistance is constant.

  This relation can only be met by

  ohmic material such as resisitor

  and not to non ohmic material

  such as bulb.

  V=IR

  I=V/R

  R=V/I
• POWER: the use or production of energy per second (P=E/t)

  Energy= V.q (Vicky)

  P= VI (ViP)

  since V=IR, so:

  P=∆ E/t =W/ t P= V2/R

  = V.q/t= VI

  P= I2.R

  Remember: I = q/t

  P= Power(Watt) W=work(Joule)

  q= charge(coulomb) E=Energy(Joule)

  t = time (second)

  V= Voltage(volt) I = current (A)
• EMF (Electromotive Force)

  EMF is the maximum voltage that a voltage

  source (such as battery) can produce. In

  reality the voltage produced in circuit is

  lower because of internal resistance inside

  the voltage source. Example: EMF battery is

  1.5 V but voltage used in circuit using the

  battery is 1.4 V
• Resistor:resistance component to control current

  Resistor ---- a component with fixed resistance.

  Variable resistor (rheostat)---resistor with varieties of

  resistance

  Thermistors---- resistor with temperature depended

  resistance. Higher resistance when it is cold, lower resistance

  when it is hot.

  Light dependent resistors (LDR)---resistor with light

  depended resistance. High resistance in the dark, low

  resistance in the light.
• 1. SERIES CIRCUITS

  +: It is easy to make a series circuit where the components are

  connected end-to-end, one after the other

  -: but when one component is not working the circuit is off.

  It has the same current through out the circuit, I =I1=I2=...

  The voltage,the resistance and the power is divided,

  Vtotal=Vsupply=V1+V2+...., R=R1+R2+...., P total =Psupply=P1+P2+...
• 2. PARALLEL CIRCUITS

  +: The circuit is not off when one component is not working.

  -: but it is difficult to assemble the circuit.

  It has the same voltage through all paths of the circuit, V =V1=V2=...

  The current and the power is divided,

  Itotal=Isupply=I1+I2+...., P total =Psupply=P1+P2+...

  The resistance is added in a way that : 1/Rtotal = 1/R1+1/R2+.....
• answer the blank

  A) switch open

  B) switch closed

  C) Battery

  D) diode

  E) resistor

  F) variable resistor

  G) LED

  H) LDR

  I) Thermistor

  J) ammeter

  K) voltmeter

  L) fuse

  M) lamp