Transcript
Power sourceTo supply
electrical power
ConductorTo conduct electricity
A device that uses energy
A switch that controls the flow of electricity is a good addition
Basic Circuit
Conventional Current
πβElectrons are
supplied at the negative pole of
the battery
Flow from negative to
positive
Electrical current is the flow of electrons
Conventional Current
Historically it was thought electricity was the flow of +
charges
Flow from positive to negative
We still use the convention today
β’ Symbol: Vβ’ SI-Unit: Volt (V)β’ Formula :
Where V = Potential difference (V)W = Work done/energy
transferred (J)Q = Charge transferred (C)
Potential DifferenceThe electrical work done per unit charge
Potential Difference: EMF
Electromotor Force:The maximum amount of electrical energy that a battery can supply to the charge that flows
through it
Potential Difference:Example 1
10 J energy is transferred when 5 Coulomb charge moves from point A to
point B. Calculate the potential difference between the two points.
The rate at which charge flows
⒠Symbol: I⒠SI-Unit: Ampère (A)⒠Formula :
Where I = Current (A)Ξt = Time (s)Q = Charge transferred (C)
Current
1 Ampère is the current when 1 Coulomb charge moves past a point in 1 second
Current: Example 2It takes 5 C charge 2 min to move from point A to point B. Calculate the current
in the wire.
Current: Example 3Calculate the current if 10 J energy is
converted to heat by a lightbulb in 50 s. The potential difference over the ends of
the lightbulb is 5 V.
Resistance
Magnified representation of a wire
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β’ Delocalized electrons collides wit positive atomic rests
β’ Causes Resistance
Tendency to inhibit the flow of electrons
Resistance: Factors
Resistance increases if temperature increases
Resistance decreases if thickness increases
Resistance: Factors
Resistance increases if length increases
Different materials does not conduct electricity to the
same extent
ResistanceThe relationship of the potential difference (V) across a component to the current (I) through
that component
β’ Symbol: Rβ’ SI-Unit: Ohm (Ξ©)β’ Formula :
Where R = Resistance (Ξ©)V = Potential difference (V)I = Current (A)
ResistanceA conductor has a resistance of 1 Ξ© if a current
of 1 A flows through it while the potential difference across the ends of the conductor is
1 V
V
I R
Resistance: Example 4The ammeter reading is 2 A
and the Voltmeter
reading is 10 V.
a) Calculate the resistance R.b) What is the emf of the battery?
Series CircuitsResistors in series act as voltage dividers
while the current stays the same
π π=π 1+π 2
Series Circuits: Example 5
Each cell has an emf of 10 V. The resistors have the
following resistances:R1= 3 Ξ©; R2 = 2 Ξ©; R3 = 5 Ξ©
Calculate:a) The total
voltageb) Total
resistancec) Ammeter
Readingd) The readings
on each of the voltmeters
Advantage:If one lightbulb fuses the other will still work
Disadvantage:Increases electricity usage
Parallel Circuits
Parallel Circuits1π π
=1π 1
+1π 2
+1π 3
π π=π 1=π 2=π 3
πΌπ=πΌ 1+ πΌ2+πΌ 3
V
I R
Parallel Circuits: Example 6
Each cell has an emf of 1,5 V. The ammeter
readings are as follows:A1= 1 A; A2 = 2 A
Calculate:a) The total voltageb) Total resistancec) The readings on
each of the voltmeters
d) Each of the resistances
Combination CircuitsResistor in series with parallel connection
1π π
=1π 2
+1π 3
π π=π 1+π π
Calculate Rp
π π=π 2=π 3
π π=π 1+π π
Calculate RT
Combination CircuitsResistor in parallel with series connection
1π π
=1π π
+1π 3
π π =π 1+π 2
Calculate Rs
π π=π π =π 3
π π =π 1+π 2
Calculate RT
The potential difference across R1 is 10 V and the reading on A1 is 0,4 A. The resistances of R2 and R3 is 45 Ξ© and 157,5 Ξ© respectively.
a) What is the reading on V1 if switch S2 is open?
b) What is the potential difference over the battery if switch S2 is open?
Both switches are now closed.
c) Calculate the resistance of R1.
Combination Circuits: Example 7 Contd.
d) Calculate the total resistance.e) What is the reading of V1?f) What is the readings on A2 and A3?g) What is the current through R3?
The switch S2 is now open.
h) What is the new readings on A1 and V1?i) How did the voltage across resistor R1
change? Explain why
Combination Circuits: Example 7 Contd.
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