Unit 1 Chapter 2 : Potential differencefptcu.com/Gep Files/physics 2/Lecture2 Physics.pdf · 1. Battery (( Electric current resource )) 2. ... the symbols that you will find it in

Unit 1

Chapter 2 : Potential difference

Dr. Mohamed Adel

Let’s remember the Electric circuits

• The simple electric circuit consists of:

1. Battery (( Electric current resource )) 2. A lamp. 3. Wires (( to connect the battery to the lamp))

The electric circuit

if the circuit is:

• Closed :

• The electric current will pass through the circuit.

• Opened (( the parts are not connected )) :

• The electric current will not pass through the circuit.

Illustrating videos

Before we start our chapter you should know also some of the symbols that you will find it in the electric circuits

• In this chapter we will discuss three concepts:

1- Electrical potential of a conductor.

2- Potential difference between two points.

3- Electro motive force (E.M.F)

Electric potential determine the way of transfer of electrical energy as it transfers from objects of higher potentials to those of lower potentials as the following:

When two charged conductors touch & they have different potentials, electric charge

flows from the conductor with high electric potential to the conductor with low

electric potential.

High electric Low electric

Potenial potenial

Until both have equal electric potential

Flow of charge

So. The electric potential is

• the state of the electric conductor which determines the transfer of electricity to or from the conductor when connected to another conductor.

Measuring device of potential difference

The voltammeter is connected in parallel

So, The potential difference is the reason of moving of the charges in

the wire

The electromotive force (emf): it is the total work done to transfer a unit charge of one

coulomb throughout the circuit outside and inside the source

- Electromotive force measuring unit is volt

What’s the difference between e.m.f and potential difference

• Both of them causing the current to flow.

• Potential difference is measured across a certain

resistance or a device when the circuit is closed.

• E.m.f is measured between the two poles of battery

when the circuit is opened.

Solved problems

>> What’s the potential difference produced from a work of 2400 joules in order to transfer 10 coulombs between two points?

The Answer

V = W

Q

Given:

V= ? W = 2400 J Q = 10 C

You do not need to re-arrange the formula.

Directly substitute the given measured values.

V= 2400

10

V = 240 Volts

>> what’s the work done to transfer 100 coulombs between two points the potential difference between them is 220 volts?

The Answer

V = W

Q

Given:

V= 220 V W = ??? Q = 100 C

You need to re-arrange the formula..

W = V Q

W = 220 x 100 = 22000 Joules.

When 5 C of charge are moved between two points in an electric field 20 J of work are done. Calculate the potential difference

between the two points.

The Answer

V = W

Q

Given:

V= ??? W = 20 J Q = 5 C

You do not need to re-arrange the formula.

Directly substitute the given measured values.

V= 20

5

V =4 Volts

Illustrating videos

Try with me to conclude the differences between electric potential, potential differences and electromotive force