Potential differentPotential different is difined as electric work/energy needed to flow the positive electric charge to another point.

+QW

•A

•B

High potentialVA

Low potentialVB

Q

WVor

Q

WV

V = potential different ( J/C = volt = V )W = electric work/energy ( J = joule)Q = electric charge ( C = coulomb )

BA VVVV

TASK1. 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?

Electrical measuring instruments

1. The Voltmeterto measure the electrical potential difference or voltage.

Symbol:

The Voltmeter installation: Parallel

2. Ammeterto measure electrical current.

Symbol:

Installation of ammeter: Series

How to read ammeter and voltmeterThe maximum scale

Appointed scale needle

Measuring limit

Measuring results =Appointed scale needle

The maximum scalex Measuring limit 34

100X 1A = 0.34 A=

The maximum scaleAppointed scale needle

Measuring limit

Measuring results =Appointed scale needle

The maximum scalex Measuring limit 40

100X 5V = 2 V=

Ohm's Law

S

If the switch S is closed then the electrical current flowing in the circuit.

According to Ohm:electrical current is proportional to the potential different and inversely proportional to the resistance.

Formula

R

VI or RIV .

V = potential different ( volt = V)I = intensity of current / current ( ampere = A)R = resistance ( ohm = Ω )

R

VI

Relationships between variables in Ohm's law.

or RIV .

1) An electric current is proportional to the potential different.

2

1

2

1

V

V

I

I

I1 = initial electric current. ( A, mA)I2 = final electrical current. (A, mA)V1 = initial potential different (volt = V )V2 = final potential different ( volt = V )

V-I graph or I-V graph

V (potential different)

I (electric current) V (potential different)

I (electric current)

or

2) Electric current is inversely proportional to resistance.

1

2

2

1

R

R

I

I

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

I (electric current)

R (resistance) I (electric current)

R (resistance)

or

TASKV (potential different)

I (electric current)

A

B

1)

Which has a greater resistance?

2) V (volt)

I (mA)Ix = ?

12

3

200

3) I (A)

R (Ω)150

0.6

0.2

Rx = ?