This document provides information about electrical principles and DC circuits. It includes definitions of key concepts like electric current, Ohm's law, resistance, energy, and power. Kirchhoff's laws are introduced. Example calculations are shown for current, potential difference, resistance, energy, and power. Resistors in series and parallel circuits are discussed.

1. Great Crystal School & Course Center
Fundamental Electrical &
Electrical Principles
AS & A Level

2. Gustav Robert Kirchoff
Scientist who discovered kirchoff's laws

3. Our
Study
Ampere, Coulomb, Electron, particular different
Electric Curent
01
Resistor, Volt, Current
Ohm’s Law
02
Watt, Joule, Ohm, Current,
Energy (W), Power (P), Resistance (R)
03
length (l), Area (A), Constanta
Resistance (R)
04

4. Electric current is the rate at
which free electrons can be made to
drift through a material in a particular
direction.
In other words, it is the rate at which
charge is moved around a circuit.
Since charge is measured in
coulombs and time in seconds then
logically the unit for electric current
would be the coulomb/second
Electric Current
In fact, the amount of current
flowing through a circuit may be
calculated by dividing the amount of
charge passing a given point by the
time taken.
The relationship between current,
charge and time can be expressed
as a mathematical equation as
follows:

5. A charge of 35 mC is
transferred between two
points in a circuit in a time
of 20 ms. Calculate the
value of current flowing.

6. This states that the p.d.
developed between the two ends of
a resistor is directly proportional to
the value of current flowing through
it, provided that all other factors (e.g.
temperature) remain constant.
Writing this in mathematical form we
have:
Ohm’s Law
This can only be achieved by
introducing a constant of
proportionality; in this case the
resistance value of the resistor.

7. If a p.d. of 24 V exists
across a 15 resistor then
what must be the current
flowing through it?

8. Energy (W) is the property of a
system that enables it to do work.
Whenever work is done energy is
transferred from that system to
another one.
The most common form into which
energy is transformed is heat.Thus
the heat produced (or energy
dissipated) is given by the equation :
Energy (W)
Applying Ohm’s law as
shown in equations
or :

9. A current of 200 mA flows
through a resistance of
750 for a time of 5
minutes.
Calculate (a) the p.d.
developed,
and (b) the energy
dissipated.

10. Power (P) is the rate at which work
is done, or at which energy is
dissipated. The unit in which power
is measured is the watt (W).
Power (P)
Applying Ohm’s law as
shown in equations

11. A resistor of 680 , when
connected in a circuit,
dissipates a power of 85
mW.
Calculate (a) the p.d.
developed across it,
and (b) the current flowing
through it.

12. Power (P) is the rate at which work
is done, or at which energy is
dissipated. The unit in which power
is measured is the watt (W).
Resistance (R)
where :
l = length (in metres)
A = csa (in square metres)
csa = cross-sectional area
(csa)
the actual material used
its temperature

13. A coil of copper wire 200
m long and of csa 0.8 mm
2 has a resistivity of 0.02
m at normal working
temperature.
Calculate the resistance of
the coil.

14. Summary Introduction
take a note, please

15. Current, capacitance, quantity, potential
NO 1

21. Great Crystal School & Course Center
D.C. Circuits
AS & A Level

22. Gustav Robert Kirchoff
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23. Our
Study
Parallel Circuit, Circuit resistance, Circuit Current, voltage
developed across each resistor, power disspated
Resistors in Series & Parallel
01
Resistor, Volt, Current
Ohm’s Law
02
Watt, Joule, Ohm, Current,
Energy (W0, Power (P), Resistance (R)
03
length (l), Area (A), Connstanta
Resistance (R)
04

25. Resistors in Parallel
When resistors are joined ‘ side-by-side ’ so that their
corresponding ends are connected together they are said
to be connected in parallel.

26. Circuit
Sample

27. S W
O T
STRENGTHS
THREATS
WEAKNESS
OPPORTUNITIES
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According to Kirchhoff’s Current Law, the algebraic sum of currents at any
node of a circuit is zero. The total current entering a junction is exactly equal
to the total current leaving the junction. This law is based on the
Conservation of Charges.
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30. V gain/ V out
NO 2

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