Direct current analysis involves defining electric current as the flow of electric charges through a closed circuit. Some effects of electric current include magnetic, thermal, chemical, and motor effects. Measuring instruments in electricity include voltmeters, ohmmeters, and potentiometers. Kirchoff's laws govern the analysis of electric circuits, with the first law concerning junctions and the second concerning closed loops. Factors that affect resistance include length, temperature, cross-sectional area, and material of the conductor.

1. DIRECT CURRENT ANALYSIS

2. Current electricity
Electric current is defined as the time
rate of flow of electric charges around
a closed circuit.
Mathematically, I=
𝑸
𝒕
,
𝑺. 𝑰 𝒖𝒏𝒊𝒕 𝒊𝒔 𝒂𝒎𝒑𝒆𝒓𝒆 𝑨

3. EFFECTS OF ELECTRIC CURRENT
•MAGNETIC EFFECT
•THERMAL/HEATING EFFECT
•CHEMICAL EFFECT
•MOTOR EFFECT

4. A simple Electrical Circuit

6. MEASURING INSTRUMENTS IN ELECTRICITY

7. DEFINITION OF TERMS
• ELECTROMOTIVE FORCE(E)
• EMF is defined as the potential
difference across the terminals
of a cell when the cell is in open
circuit. It is measured with
potentiometer and in volts(V)
• POTENTIAL DIFFERENCE(V)
• The potential difference
between two points in an
electrical circuit is defined as
the work done in moving a unit
charge from one point to
another. It is measured with a
voltmeter in volts(V).

8. DEFINITION OF TERMS (cont.)
• ELECTRICAL RESISTANCE(R)
It is the opposition offered to the flow of electric current in a
conductor. It is measured with an ohmmeter in ohms(Ω).

9. OHM’S LAW
• It states that the current passing through a metallic conductor is
directly proportional to the potential difference across its ends
provided temperature and other physical conditions remain constant.
It can be expressed mathematically as; 𝒗 = 𝑰𝑹

10. VERIFICATION OF OHM’S LAW

11. VERIFICATION OF OHM’S LAW
I/A V/V 𝑽
𝑰
/Ω

12. Ohmic and Non Ohmic Condutors

13. COMBINATION OF RESISTORS
• SERIES COMBINATION OF RESISTORS

14. SERIES COMBINATION OF RESISTORS

15. SERIES AND PARALLEL CIRCUIT COMPARED

16. INTERNAL RESISTANCE OF A CELL

17. TEMPERATURE COEFFICIENT OF RESISTANCE(𝜶)
• The temperature coefficient of resistance is a quantity that
determines how resistance varies with temperature.
Mathematically, 𝜶 =
𝑹𝑻−𝑹𝟎
𝑹𝟎𝑻
… … … … … … … . 𝟏
Where T is the temperature of the conductor
𝑹𝟎 is the resistance of the conductor at 0℃
𝑹𝑻 is the resistance of the conductor at temperature T

18. TEMPERATURE COEFFICIENT OF
RESISTANCE(𝜶)
• From equation 1
• 𝑹𝑻 = 𝑹𝟎(1+ 𝜶T)
• EXAMPLE(1)
• Calculate the resistance of tungsten at a temperature 20 ℃ if its
temperature coefficient of resistance is 0.006 ℃−1
. At 0 ℃ tungsten
has a resistance of 15 Ω.

19. RESISTIVITY
• Resistivity of a wire is defined as the resistance of a wire of a unit
length and a unit cross-section area. The unit is the ohm-metre.
Mathematically, 𝜌 =
𝑅𝐴
𝑙
If d is the diameter of the wire(conductor), then
𝐴 =
𝜋𝑑2
4
→ 𝑅 =
4𝜌𝑙
𝜋𝑑2

20. FACTORSTHAT AFFECT THE RESISTANCE OF A
CONDUCTOR(WIRE)
•LENGTH OF CONDUCTOR
•TEMPERATURE
•CROSS-SECTIONAL AREA
•MATERIAL OF THE CONDUCTOR

21. RESISTOR COLOR CODING

22. KIRCHOFF’S FIRST LAW
•It is also called the Junction or current law.
•It states that the sum of current arriving
at a junction in an electrical network is
equal to the sum of current leaving the
junction.

23. KIRCHOFF’S LAWS

24. The First law stated as the Principle of
conservation of charge.
•The principle of conservation of charge
in a network states that the net charge
flowing at any given point in a network
is zero.

25. KIRCHOFF’ SECOND LAW
•The second law is also called loop or voltage law.
•It states that in a closed loop of an electrical
network, the algebraic sum of the e.m.fs is equal
to the algebraic sum of the p.ds around the
same loop.

26. KIRCHOFF’ SECOND LAW

27. STATEMENT OF THE SECOND LAW AS
PRINCIPLE OF CONSERVATION OF ENERGY
•If a charge moves around a closed loop in a
circuit, it must gain as much energy as it
loses.
•Hence, the gain in electrical energy by the
charge = corresponding losses in energy
through resistances.

28. CONDITIONS UNDER WHICH THE LAWS HOLD
•In the case of the first law, a
junction in a complete circuit must
be considered.
•For the second law, a closed loop
must be considered.

29. DEFINITION OF TERMS
• JUNCTION:
• NETWORK:

30. THE WHEATSTONE BRIDGE CIRCUIT

31. THE WHEATSTONE BRIDGE EQUATION
𝑅1
𝑅2
=
𝑅3
𝑅4

32. METER BRIDGE

33. METER BRIDGE EQUATION
𝑅
𝑆
=
𝑙1
100−𝑙1

34. DETERMINATION OF RESISTIVITY OF A WIRE
USING THE METER BRIDGE.