Transcript Current and Charge

Current & Charge
New vocabulary .
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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.
Semi-conductor devices consist of a diodes, transistors, SCR’s, triacs, and LED’s
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
1 Coulomb of charge (6.25 x 1018
electrons) passes a point each second,
the current is 1 Ampere.
If
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 radio
B- 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?
Conduction in liquid and gases :
Current and drift velocity
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.
I=nAve
I = current
N = number of electron
A = part of a wire of cross-sectional
V = drift velocity
E = 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
Pop Quiz
Q1
• One example of :
• A- Semiconductor
• B- Insulator
• C- Conductor
Q2:
• What is the name of this device :
Q3 :
• What is the unit of :
• A- Current
• B- Charge
Q4 :
• A solution of sugar in pure water will not
conduct . Why not ?
Q5 :
• When can air be a conductor of electricity ?
Potential Difference
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.
Charges
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 difference
W = energy transferred
Q = 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 .
How do you measure p.d.?
You use a voltmeter which is placed across the lamp as
shown
W = I t p.d
Q1 : a 230v kettle transfers 6.9x105 j of energy in 5 minutes .
What is the current In the kettle ?
Electrical Resistance
Most
materials offer some resistance to the flow
of electric charges through them. This is called
electrical resistance.
Complete the table
Voltage Current Resistance
Definition
Symbol
Unit
Device
Resistance
Resistance
Material
of a conductor depends on:
- Gold is best
Cross
section - thick wires have less resistance
than thin wires
Length
- longer conductors have more
resistance.
Temperature
- higher temperature means more
resistance for most conductors
Ohms’ Law
V
In
= IR
symbols:
V
R
I
Complete the table
Voltage
(volt)
Current
(A)
110
50
30
44
15
Resistance
(ohm)
2
20
60