ElectricityReyna Clarissa – 10

CHAPTER 37

Static Electricity

Positive and negative charges

There are two kinds of electric charge. Positive charge (+) and negative charge (-). Like charges (+ and + or – and – ) repel, whereas unlike charges (+ and -) attract. The force between them decreases when the distance increases.

Charges, atoms and electronsSmall central nucleus which contains positively charged particles called protons, are surrounded by an equal number of negatively charged called electrons. A electrically neutral atom has the same number of protons and electrons. Every nucleus, except hydrogen, contains uncharged particles called neutrons.

Electrons, insulators and conductors An electroscope is a device to determine or measure the presence of electrostatic charges. In an insulator all electrons are bound firmly to their atoms and in a conductor some electrons can move freely from atom to atom. Good insulators are plactics such as polyetene, cellulose acetate, Perspex and nylon. All metals and carbon are good conductors. Wood, paper, cotton, the human body and the Earth are poor conductors and insulators.

Electrostatic Induction

Electrostatic induction is a quick way of using a charged object to give something a charge, of the opposite sign, without losing any of the original charge. The attraction of an uncharged object by object near it is due to electrostatic induction.

Dangers of static electricityLightningRefuellingOpering TheatresComputers

Uses of static electricityFlue-ash precipitationPhotocopiersInkjet Printers

Van de Graaff generator

A Van de Graaff generator is an electrostatic generator which uses a moving belt to accumulate very high voltages on a hollow metal globe on the top of the stand.

The basic use of a Van de Graaf generator is to separate electric charges and build them up, frequently for demonstration purposes

Electric Fields

It is the region of space where an electric charge experiences a force due to other charges.

CHAPTER 38

Electric Current Electric current is a flow of

electric charge through a medium

An electric current has three effects that reveal its existence : Heating and lightning Magnetic Chemical

•The ampere and the coulomb▫Current is measured in ampere (A). One milliampere (mA) is one-thousandth of an ampere. Ammeter is the measuring instrument of current.

▫The unit of charge, the coulomb (C), is defined in terms of the ampere. 1C = 1A s.

Current must have a complete path or circuit of conductors if it is to flow. These symbols are the commonly-used ones in a circuit.

• Circuit diagrams

Series and parallel circuitsSeries

In a series circuit, the current is the same at all points in a circuit but it has different numbers of potential different.

Parallel In a parallel circuit, the potential difference is the same at

all points in a circuit but it has different numbers of current.

CHAPTER 39

Potential difference

The battery is said to have a potential difference (p. d.) at its terminals. Potential difference is measured in volts (V) and the term voltage is sometimes used instead of p.d.

Its defined by V = I x R

Energy transfers and p.d. Energy in a circuit is supplied from a source such

as a battery and is transferred to other forms of energy by devices in the circuit.

The volt The p.d. between two points in a circuit is 1 volt

of 1 jould of electrical enegry is transferred to other forms of energy when 1 coulomb passes from one point to another.

▫Cells, batteris and e.m.f. A battery consists of two or more electric cells. Greater voltages are obtained when cellls are joined in series. When no current is drwn from a battery it is said to be an open circuit and its terminal p.d. is a maximum. The maximum voltage is called the electrmotive force (e.m.f)

▫Voltages round a circuitThese are how to calculate the total of V in

a circuit; Series : V= V1+V2+V3 Parallel : V1=V2

CHAPTER 40

The opposition of a conductor to current is called its resistance. A good conductor has a low resistance, a poor conductor has a high resistance.

It increases as its length increases, as its cross-section area decreaes, and it depens on the material. Silver and copper are the best conductors.

Resistance

The Ohm

The resistance is defined by R = V.I and it is measured in Ohms (Ω).

The ohm is the resistance of a conductor in which the current is 1 when a voltage of 1 volt is applied to it.

Resistors Conductors intended to have resistance are

called resistors. They arre usually made from wires of special alloys or carbon.

Rheostat is a variable resistor, used for adjusting the current, can also work as a potential divider to adjust the p.d. in a circuit.

These are how to calculate the total of resistance in a series;

-Series R = R1+R2+R3

-Parallel1/R =

1/R1+1/R2+1/R3

The resistor colour code

• Resistivity

The resistivity of a material is numerically equal to the resistance of a 1m length of it of corss-section area 1m².

CHAPTER 41

Capacitors

A capacitor stores electric charge and its usefu in many electronic circuits. The insulator called the dielectris is sandwiched between two parallel metal plates.

A capacitor can blok d.c. and passes a.c.

Capacitance

The more charge a capacitor can store, the greater is its capacitance (C). It is measured in farads but smaller units like microfarad are more convinient.

Types of capacitor Practical Capacitor

Plastics are the commonly-used material for this kind of capacitor, with films of metal being deposited on the plastic to act as the plates.

Electrolytic capacitor It has a very thin layer of aluminium oxide

as the dielectric between two strips of aluminium foul, giving large capacities.

CHAPTER 42

Electric powerEnergy transfers were measured by the work

done and power was defined by the equation; power = work done/time taken = energy

taken/time taken

Lamp and motor can be used to measure the electric power in a circuit.

Instead of using ammeter and a volmeter to measure the electrical energy transferred by an appliance, a joulemeter can be used to obtain it directly in joules.

•Electric lightning▫Filament lamps

▫Fluorescent strips

• Compact fluorescent lamps

Electric heating› Heating elements

› Three-heat switch

• Fuses

CHAPTER 43

Electricity in the home

These are some aspects that are important to be concerned for electricity in the home; circuits in parallel, switches and fuses, staircase circuit, ring main circuit, fused plug, earthing and safety, circuit breakers and double insulation.

• Paying for electricity– A killowat-hour is the electrical energy used by a 1

kW appliance in 1 hour.• Dangers of electricity– Electric shock

– Fire risks

THANK YOU FOR

STOPPING BY!Use electricity wisely! : )