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Electricity
Originally called the electrical effect!
Discovered aproximately 2700
years ago!“Electrical” come
from the greek word Elektron, meaning
Amber
Amber was found to attract objects after it
was rubbed against wool
Electrical charge
• To better understand electricity we must look at the atomic model.
-
-
-
+ ++Protons
Neutrons
Electrons
Electrical charge
• Electrical charge comes from the protons and electrons of an atom. The protons carry the positive charge, while the electron carries the negative charge.
• Negatively charged bodies carry more Electrons then Protons
• Positively charged bodies carry more Protons then Electrons
Electrons can be removed from atoms – Positive: electrons are stripped off– Negative: extra electrons are added
Electrical charge• Electrical charge is measured in Coulombs
(repressented by the symbol q )• 1 Coulomb is equal to the electrical charge of a
single Electron. 1 Electron carries a charge of 1.602 x 10 -19 C
• Identifying electrical charges has allowed scientists to discover:– Opposite charges attract each other(+ and -)– Like charges repel each other (+ and +, or – and -)
This is refered to as the “Forces of attraction and Repulsion”
Electrical charges
• An object is charged when an imbalance is created in the electrical charge of that object
• When an object is charged the charge is spread evenly across the surface while the interior remains neutral.
Conductors and Insulators
• Objects can be classified into three categories depending on how they react to receiving electrical charges.– If the substance allows the flow of electrical charge
it is considered a conductor– If the substance stops the flow of electrical charge it
is considered an insulator– If the substance slows the flow of electrical charge
or has varying conductivity it is considered a semiconductor
Electrical charge
Open your text books to pages 140 – 143 and complete the handout #19
Electrical Field • The electrical field of an object is the area in
which the electrical charge of one object can act on another charged object.
Static Electricity
• Electrostatic electricity deals with the electrical phenomena related to insulated charges which are generally at rest.
The word static comes from the greek word
Statikos, meaning “causing to stand
Static electricity
• Electroscopes can be used to detect static electricity.
Charging an object
• There are three ways to charge an object• Friction• Conduction• Induction
Charging via Friction• Rubbing two neutral bodies together often
results in the transfer of electrons, creating two oppositely charged bodies.
Plastic
Sulfur
Gold
Nickel, Copper
Hard Rubber(ebonite(bow
ling balls))
Wood, Yellow
Amber, Resin
Cotton
Paper
Silk
Lead
Wool
Glass
Tendency to acquire a
negative charge
(-)
Tendency to acquire a
Positive charge
(+)
Charging via conductionWhen an insulatd neutral object comes into contact
with an object with an excess charge, the two object can share the charge, resulting in two weaker charges
Charging via InductionWhen a neutral object is approached with an object
with an excess charge, the neutral object can achieve an unbalanced charge provided it is not insulated .
Electrical charge
Open your text books to pages 145 – 148 and complete the handout #19
Dynamic Electricity
• Dynamic means electricity in motion
• Static electricity refers to electrons moving about at random
• Electrical current is the orderly flow of negative charges carried by electrons
Electric current is analogous to water flow. Which elements correspond in the two systems?
Electric Current: Flow of Charges
Electric Current and Water Flow
Electrical Current• Current Intensity– Measured in Amperes(amps)• Refers to how much charge passes a given point every
second• 1 amp = 1 coulomb of charge every second
– Current intensity can be determined by the the following equation
I=q/ΔtI = current intensity(amps)
q = charge(coulombs)Δt = time(sec)
Practice
• If 300 c pas through a circuit in 2 seconds what is the current intensity?
150 A• If a light needs 3 amps worth of current to work for
1 minute what charge is require?180 C
• If the projector requires 5 amps worth of current and is supplied with 400 c how long could it run for?
80 seconds
Electric CircuitsElectric circuit–Unbroken path of material carrying
electricity– Electrical conductor
Circuit– A source of energy (battery)– A loop of wire– A device to use the electrical energy
Potential difference
The amount of energy transferred between two points in a circuit (volts)
Calculated using the following formulaV=E/q
V = Potential difference(volts)E = Energy transferred (Joules)
q = charge (Coulombs)
Practice
• The circuits in the school wall have a potential difference of 120 V. How much energy is provided by a charge of 300 c?
360 00 J• If a cars internal circuits receive 400 00 J from
a charge of 125 c what is the potential difference of the circuit?
320 V
Resistance• Refers to the ability of a material to slow the flow of electrical
current. Measured in Ohms (Ω)• See P 153 of your text for table 5.22 which explains the
different factors affecting the resistance of a substance to current flow.
Ohm’s Law
V=RIV= Potential difference (Volts)
R = Resistance (Ohms)I = current intensity (Amps)
For any resistance(Ω) the potential difference(V) is proportional to the current intensity (A)
Practice
• What is the resistance of a circuit with a potential difference of 200 V and a current intensity of 10 A?
20Ω• What is the current intensity of a circuit with a
resistance of 15Ω and a potential difference of 30 V?
2 A
Electrical powerHow much energy a device can transform, or the
amount of work it can perform.Measured in Watts(W)
Watts are a function of energy over time;1W = 1J/1S
Electrical power is calculated using the followingPe = W/Δt
Pe = Watts(electrical power)W = Work(J)Δt = time(s)
Power and Electrical Energy
Types of Circuits
• Series circuits• Parallel Circuits
Pe = W/Δt or Pe = V/I Pe = Watts(electrical power)
W = Work(J)Δt = time(s)
V = Potential difference(volts)I = current intensity (Amps)
V=RIV= Potential difference (Volts)
R = Resistance (Ohms)I = current intensity (Amps)
V=E/qV = Potential difference(volts)E = Energy transferred (Joules)
q = charge (Coulombs)
I=q/ΔtI = current intensity(amps)
q = charge(coulombs)Δt = time(sec)