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New vocabulary .
• Nucleus • Electron (-)• Proton ( +)• Neutron (0)• Ion• Current• Semiconductor• Conductor • Insulator
Diagnostic test
Q1 : Draw the structure of an atom :
Q2 : Where do you use the electric energy ?
The electric energy change in to …………….. In the …………….
Q3 : How does the electric energy move from the power station ?
Flow through cables .
Q4 : Draw the direction of ( electron and conventional current ) in the circuit ?
A semiconductor :is a material that has electrical conductivity between those of a conductor and an insulator; it can vary over that wide range either permanently or dynamically.
Semiconductors are essential in electronic technology. Semiconductor devices, electronic components made of semiconductor materials, are essential in modern consumer electronics, including computers, mobile phones, and digital audio players. Silicon is used to create most semiconductors commercially.
Electric current Current is measured in amperes (A) using an ammeter .
1A=6X1018 electrons in each second .
The charge on 1 electron =1.6x10-19 C
Current ( I ) amps =
Charge ( Q ) coulomb / time ( t ) second
Measuring Current
If 1 Coulomb of charge (6.25 x 1018 electrons) passes a point each second, the current is 1 Ampere.
So, 1 Ampere = 1 Coulomb
Q1 : current of 2A passes through a lamp for 3 minutes.A- how much charge passes through the lamp.B- how many electrons pass through the lamp.
Q2 : current of 15A passes through a radio for 4 minutes.A- how much charge passes through the radioB- how many electrons pass through the radio.
Q3 :If there is a current of 10 amperes in a circuit for 10 minutes, what quantity of electric charge flows in through the circuit?
Q4:. How much current must there be in a circuit if 100 coulombs flow past a point in the circuit in 4 seconds?
Q5 :. How much time is required for 10 coulombs of charge to flow past a point if the rate of flow (current) is 2 amperes?
Electrons in a circuit do not move quickly - they actually “drift” at about 1 mm/s.It is the electric field that moves quickly - at about the speed of light - through the circuit and carries the energy.
Current and drift velocity
I = n A v e
I = currentN = number of electron A = part of a wire of cross-sectional V = drift velocityE = number of coulombs per second
Q1 : copper contain 1x1029 free electron per m3. What is the drift velocity of electrons In a copper wire of cross – sectional area 0.55 mm2 carrying a current of 0.35A?
1m2= 1000mmx1000mm=1x106 mm2
1mm2= 1/1000m x 1/1000m=1x10-6 m2
Charges can “lose” potential energy by moving from a location at high potential (voltage) to a location at low potential. Charges will continue to move as long as the potential difference (voltage) is maintained.
Potential difference or ( p.d.)Connecting a cell or battery in a complete circuit causes a potential difference across each component. Potential differences are measured in volts (V). The number of volts tells you the amount of energy given up as the current flows through a component. All of the energy put in by the cell is used up as the current flows through the component
p.d.(Volt) = W( joule ) /Q(coulomb )
p.d.=Potential differenceW = energy transferredQ = charge
Example
Q1 : Calculate the p.d. across a wire if the energy transferred is “A- 600 j when a charge of 50C passes through it .B- 450 j When there is steady current of 0.5 A for 20 second .
Q2 : A lamp has a p.d. of 12 v across it. Calculate how much electrical Energy is transferred when :A- a charge of 400 C passes through it .B- a current of 2.5A passes through it for 30 second .
Electrical Resistance
Most materials offer some resistance to the flow of electric charges through them. This is called electrical resistance.
Resistance
Resistance of a conductor depends on:
Material - Gold is best
Length - longer conductors have more resistance.
Cross section - thick wires have less resistance than thin wires
Temperature - higher temperature means more resistance for most conductors