1) Potential difference is defined as the electric work or energy needed to move a positive electric charge from one point to another. It is measured in volts. 2) If 90 Joules of electrical energy is used to transfer 30 coulombs of charge from point A at 12 volts to point B, then the potential at point B is 3 volts. 3) Electrical instruments like voltmeters and ammeters are used to measure potential difference and current respectively. Voltmeters are connected in parallel while ammeters are connected in series within a circuit.

11. Potential different
Potential different is difined as electric work/energy needed to flow the positive
electric charge to another point.
Q
+
W
•
A
High potential
VA
•
B
Low potential
VB
W
V
Q
W
or V
Q
V = potential different ( J/C = volt = V )
W = electric work/energy ( J = joule)
Q = electric charge ( C = coulomb )
V
V VA
VB

14. 1. Electrical energy of 90 joules used to transfer 30 coulombs of electric
charge from point A to point B. If the electric potential point A is 12 volts,
what is the electric potential point B?
2. Electrical charges 40 C move from point X to point Y need electrical
energy of 120 joules. If the electric potential point Y is 6 volts, what is
the electric potential point X?

15. Electrical measuring instruments
1. The Voltmeter
to measure the electrical potential difference or voltage.
Symbol:
The Voltmeter installation: Parallel

16. 2. Ammeter
to measure electrical current.
Symbol:
Installation of ammeter: Series

17. How to read ammeter and voltmeter
The maximum scale
Appointed scale needle
Measuring limit
Appointed scale needle
Measuring results =
The maximum scale
x Measuring limit =
34
100
X 1A = 0.34 A

18. The maximum scale
Appointed scale needle
Measuring limit
Appointed scale needle
Measuring results =
The maximum scale
x Measuring limit =
40
X 5V = 2 V
100

19. Ohm's Law
If the switch S is closed then the electrical current
flowing in the circuit.
S
According to Ohm:
electrical current is proportional to the potential
different and inversely proportional to the resistance.
V
I
R
V
I .R
V = potential different ( volt = V)
I = intensity of current / current ( ampere = A)
R = resistance ( ohm = Ω )

22. Relationships between variables in Ohm's law.
V
I
R
V
I .R
1) An electric current is proportional to the potential different.
I1
I2
I1 = initial electric current. ( A, mA)
I2 = final electrical current. (A, mA)
V1 = initial potential different (volt = V )
V2 = final potential different ( volt = V )
V1
V2
V-I graph or I-V graph
I (electric current)
V (potential different)
V (potential different)
I (electric current)

23. 2) Electric current is inversely proportional to resistance.
I1
I2
R2
R1
I1 = initial electric current. ( A, mA)
I2 = final electrical current. (A, mA)
R1 = initial resistance ( ohm = Ω )
R2 = final resistance ( ohm = Ω )
R-I graph or I-R graph
R (resistance)
I (electric current)
I (electric current)
R (resistance)

24. V (potential different)
A
1)
Which has a greater resistance?
B
I (electric current)
I (A)
V (volt)
2)
3)
12
0.6
3
0.2
200
Ix = ?
I (mA)
150
Rx = ?
R (Ω)