2.1 Analysing Electric Fields and Charge Flow

Analysing Electric Fields and Charge Flow

By Ms Nurul Ain Mat Aron

state the relationship between electron flow and electric current

define electric current

describe an electric field

sketch electric field lines showing the direction of the field

describe the effect of an electric field on a charge

solve problems involving electric charge and current

Objectives

Electric Charge, Q

There are two type of electric charge which are a) Positive charge (+) b) Negative charge (-)

An electron has a negative charge and a proton has a positive charge

The charge on a single electron is -1.6 x 10-19 C The charge on a single a proton is +1.6 x 10-19 C

The unit is coulomb or C

Electric Charge, Q

A body is: a) Neutral, if it has equal number of positive and negative charges. b) Negative charged, if it has more negative than positive charges c) Positive charged, if it has more positive than negative charges

Recall: 12 protons

12 neutrons

Magnesium atom

12 electrons

2+

10 electrons

Magnesium ion

Electric Charge, Q Examples

An object that is positively charges contains all protons and no electrons

FALSE

An object that is negatively charges could contain only electrons with no accompanying protons

FALSE

Like charges repel, unlike charges attract

Electric Charge, Q

Like charges repel

Electric Charge, Q

unlike charges attract

Stationary electric charges are known as static electricity

Static Electricity

Static electricity is the accumulation of electrical charges on the surface of a material

Static electricity is usually caused when certain materials are rubbed against each other

The process causes electrons to be pulled from the surface of one material and relocated on the surface of the other material.

The material that loses electrons ends up with an excess of positive (+) charges. The material that gains electrons ends up an excess of negative () charges on its surface.

Electric current consists a flow of electrons. The more charges that flow through a cross section within a given time, the larger is the current.

Therefore, an electric current is define as the rate of flow of charge

Electric Current, I

The amount of charge, Q flowing through any conductor is given by:

Electric Current, I

Q = It

A B

When free electrons move through the wire from A to B, and the electric currents flows from B to A

I

A fuse wire will blow if the current flowing through it exceeds 5.0A for a time of 80ms. a) What is the quantity of electric charge that has passed through

the fuse wire in 80ms? b) How many electrons have passed through the fuse wire in that

time, given that the charge on 1 electron is 1.6 x 10 -19 C

Problem 1

Answer: 0.40 C and 2.5 x 1018

Electric Current, I

A charge of 600 C flows through a metal conductor in every 5 minutes. What is the electric current in the conductor?

Problem 2

Electric Current, I

An electric current of 3.2mA flows through a bulb for 4 minutes. Determine a) The electric charge b) The number of electrons (the charge in an electrons, e = 1.6 x 10-19 C)

Problem 3

Electric Current, I

An electric field is a region in which an electric charge experience a force. An electric field can be represented by field lines drawn in certain pattern. The direction of the field is indicated by arrows on the lines.

Electric Field

The lines of force are directed outwards for a positive charge and inwards for a negative charge.

Electric Field

The strength of the electric field is indicated by how close the field lines are to each other. The closer the field lines, the stronger the electric field in that region.

Electric Field

The Effect of an Electric Field

The ball will still remain stationary. This is because the force exert on the ball by the positive plate is equal to the force exerted on it by the negative plate.

A ping-pong ball coated with a Conducting Material


If the ping pong ball is displaced to the right to touch the positive plate, it will then be charged with positive charge and will be pushed towards the negative plate




When the ping pong ball touches the negative plate, it will be charged with negative charge and will be pushed towards the positive plate. This process repeats again and again, causes the ping pong ball oscillates to and fro continuously between the two plates.


Spreading of a Candle Flame



The heat of the candle flame removes electrons from the air molecules around it, and therefore ionised the molecule.



If the candle is placed in between 2 plates connected to a power supply, the positive ions will be attracted to the negative plate while the negative ions will be attracted to the positive plate.

Documents

2.1 Analysing Electric Fields and Charge Flow