Current Electricity for IGCSE

1. Mr Riel Casinillo
10/25/2022

2. 1. Recall electrical symbols
2. Define the terms potential difference,
current, electromotive force.
3. Recall and use the equation linking charge,
energy transferred and voltage, and the
relevant units for these.
4. Use the equation linking charge, energy
transferred and voltage to show that the
volt is equivalent to the joule per coulomb.
10/25/2022

3.  Make the bulb light
1 with least possible wire
2 which can be turned on or off
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4.  A complete or closed path through which charge can
flow from one terminal of an electric source to the other
terminal.
 Consists of four main components
- Source of electromotive force that
drives the electric charge round the circuit
- A load on which moving
charges can do a useful job
- Conductors to connect
the components together
- Switches to open and close
the circuit
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5. Can we try to do this on our table with the
materials provided?
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6. Can we try to do this?
Nah!!! Some other
time!!! :p
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7. 10/25/2022

8. 10/25/2022

9.  Movement of
electrons
 Is formed by moving
electrons.
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10. Current Flow to Water Analogy
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11.  An electric current (I) is a measure of the rate
of flow of electric charge Q through a given
cross section of a conductor.
 In symbols,
where: I is the current (in Ampere A)
Q is the charge (in Coulombs C)
t is the time taken (in seconds s)
What is electric current?
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12. Right!!! Use an
ammeter!
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13.  Can you draw the difference?
 How about an illustration of a short-circuit?
 Can you explain why it is called a short-
circuit?
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14. An analogy of a water pump to the electromotive force
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15.  The electric force produced by the energy
source which pushes the electrons through a
circuit.
 More scientific definition:
- Electromotive force (e.m.f.) of an electrical energy
source is defined as the work done by the source in
driving a unit charge round a complete circuit.
where: Ɛ is the emf of the power supply (V)
W is the work done ( J )
Q is the amount of charge ( C )
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16. Right!!! Use a voltmeter!!!
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17.  The amount of energy which is converted
across a light bulb for each unit of charge
 More scientific definition:
◦ The potential difference between two points in an
electric circuit is defined as the amount of electrical
energy converted into other forms of energy when
one coulomb of positive charge passes between two
points.
Where V is the potential difference ( V)
W is the electrical energy ( J )
Q is the amount of charge ( C )
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18. W
V Q
Q
I t
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19. 10/25/2022

20.  Learning Outcomes:
◦ Define resistance and state that resistance is
measured in Ω
◦ State Ohm’s Law
◦ Apply the definition of resistance to solve problems
◦ Describe an experiment to determine resistance
◦ Describe the effect of temperature on resistance
◦ Sketch and interpret the I-V characteristic graphs
for ohmic and non – ohmic conductors.
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21.  A measure of how difficult it is for an electric
current to pass through a material.
 Is a property of a material
 Determines the size of electric current
passing through a material
 a.k.a “friction”
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22.  Fixed resistor
 Variable resistor

23.  This is the ratio of the
p.d. across a conductor
to the current flowing
through it.
◦ i.e. R = V
I
Unit: Ohm 
 http://micro.magnet.fs
u.edu/electromag/java
/filamentresistance/

24. -Use Ohmmeter
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25.  Rate of doing work or transfer of energy
 P = VI
 P = I2R
 P = V2/R
Where
P = Power (Watts)
I = current (Ampere)
V = Voltage (Volts)
R = Resistance (Ohms)
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26.  This states that for certain
conductors (mainly metals)
the current flowing through
them is directly proportional
to the potential difference
across them at a constant
temperature.

27.  Filament lamp
 thermistor  Semiconductor
diode

28. 1 Differentiate Ohmic and Non Ohmic Conductors
1 Plot the graph of Ohmic Conductors
1 Plot the graphs of the following:
a Filament lamp
b thermistor
c semiconductor diode

29.  Resistance depends on
◦ Temperature
◦ Material of conductor
◦ Length
◦ Cross-sectional area
Temperature
The resistance of a metallic
conductor increases as the
temperature increases e.g. copper
The resistance of a
semiconductor/insulator decreases
as the temperature increases e.g.
thermistor.

30. Length
Resistance of a uniform
conductor is directly
proportional to its length.
i.e. R  L
Cross-sectional area
Resistance of a uniform
conductor is inversely
proportional to its cross-
sectional area.
i.e.R  1
A

31. R =
A
l

Where
R = resistance (Ω)
= resistivity (Ω m)
l = length (m)
A = area (m2)


32. https://phet.colorado.edu/en/simulation/battery-resistor-
circuit