Electricity (Chapter 8)

Electric Charge

2 TYPES: Negative and Positive

Like charges  repel  whereas opposite charges attract

Conductors are materials that let electricity pass them through 

o Metals are the best electrical conductors as they have free electrons.

Insulators: materials that hardly conduct at all.

o Their electrons are tightly held to atoms and hardly move, but they can be transferred by rubbing

The SI unit of charge is the Coulomb (C).

Induced

A charge that “appears” on an uncharged object because of a charged object nearby

 For example if a positively charged rod is brought near a small piece of aluminum foil, electrons in foil are pulled towards rod, which leaves the bottom of the foil with a net positive charge.

The attraction is stronger than repulsion because the attracting charges are closer than the repelling ones.

Current

Flow of charge measured in Ampere (A) by an ammeter (connected in Series)

Voltage

Also known as Potential Difference

This is the amount of energy the cell gives the electrons it pushes out

Measured in volts by a voltmeter (connected in parallel) 

In series, volatage is equally divided amongst bulbs,

In parallel. voltage is the same as the cell providies, as each component is directly connected to the cell

Electromotive force

Maximum voltage cell can produce (EMF)

When current is being supplied, the voltage is lower because of the energy wastage inside the cell

Cell produces its maximum PD when not in a circuit and not supplying current

Convectional current

Convectional current shows the current moving from Positive to negatvie 

when in truth the electrons moves from NEGATIVE TO POSITIVE

Resistance

Resistance (Ω) = Voltage / Current 

Factors affecting resistance

Length : R (directly proportional to length)

Cross sectional area: R (directly proportional) 1/Area

Material: Better conductor, less resistance

Temperature:

Metal conductors.. Higher temp = More resistance

Semi-metal conductors... Higher termp = Less resistance

Characteristics of resistor (voltage and current graph)

Ohmic device: direct proportion

Non ohmic device:

(filament lamp) S curve

(Diode) Charge on one side only

Electrical Energy

Power = Voltage x Current

Electrical energy = Voltage x Current x Time

Series

- If one lamp breaks, they all  do (one long chain)

- Resistors: R(total) = R1+R2

Parallel

- If one lamp, breaks the others arent affected (connected separately to cell)

-Voltage is higher

-Resistors: R(total) = 1/ 1/R1 + 1/R2