Physics Assingment ( Electric Field)

8/7/2019 Physics Assingment ( Electric Field)

1/6

Along our studies, two different field forces have been introduced which are the

gravitational force and electrostatic force. As point out of earlier, these forces are capable

of acting through space and producing effect even when there is nophysical contact between

the objects involved. Field forces can be discussed in many ways and the approach is

developed by Michael Faraday in the year of 1791 1867. In this approach, an Electric

Field is said to exist in the region of space around a charge object. When another charged

object enters this electric field exerts a force on the second object. As an example, consider

the diagram below which shows an object with a small positive chargeqplaced near a second

object with a larger positive charge Q experiences an electric field, E directed as shown.

Q

++++++ q

++++++ +++

++++++

Test charge (bring near)

Hence, we define the electric field at the location of thesmall test charge to be the electric

force acting on it divided by the by the charge q of the charge. The formula is shown below.

, ( where E is electric field, F is force and q is charge)

The electric field is a vector quantity and having unitNewton per coulomb (N/C).Therefore,

the direction ofE at a point is defined to be the direction of the electric force that would beexerted on a small positive test charge placed at that point.


2/6

Once t e elect ic fiel i known at some point t e force on any particle wit charge q

placed atthat point can be calculated from a rearrangement ofthe previous equation.

F = q E

Consider a point charge , q1located a distance r from a test charge, q2.Accordign to

Coulombs Law, the magnitude ofthe force on the test charge is

F = k !q1! q2! / r2

So that, these are some information aboutthe concept ofEl ri Fi l .

Electric field is very importantto human beings to run their daily life. Nowadays, the

concept of electric field is applied in many appliances and also in certain systems. This is

because, people really understand the importance of electric force as well as electric field

usage in commercial machines and devices. These are the examples of electric field,justlike

Photostat machine, Oscilloscope and Capacitor.

T oscilloscope cathode ray tube (CRT is a vacuum tube that creates and deflects

an electron beam to form a graphicalimage representing the electrical properties of a circuit.

An oscilloscope is used to test electrical devices by displaying a graph ofthe voltage between

two points in a circuit overtime. The CRT displays this graph. Similar CRTs are used in

radar systems, televisions, and computer monitors. A glass tube contains and encloses the

oscilloscope CRT in a vacuum. The base ofthe tube plugs into the oscilloscope, while the

other end flares to a large flat area that serves as the screen. An electron gun inside produces

an electron beam that passes through two sets of deflection plates before hitting the

fluorescent screen to create an image. This device operates by creating and accelerating a

beam of electrons with an electric field. Another electric field between the deflection plates

directs the beam to the desired location ofthe display. Finally, the fluorescent screen

converts the energy ofthe electron beam into slowly emitted visible photons. Four main parts

make up the oscilloscope CRT: bulb, electron gun, deflection plates, and fluorescent screen.


3/6

The bulb encloses and holds the components of the CRT in a vacuum. It is a glass tube

shaped roughly like a flashlight. On one end of the tube is the base that plugs into the

oscilloscope and contains the leads that supply current to the components inside. The other

end is bell shaped and serves as the display. The bulb keeps the space around the CRT free of

particles of dust and air and holds down each of the components of the CRT. The deflection

plates are simply pairs of oppositely charged metal plates. There are two sets of deflection

plates which are vertical and horizontal. Each set of plates is parallel and located at the neck

of the tube. The vertical deflection plates lie horizontally but control the vertical position of

the beam. The horizontal plates are positioned at right angles to the vertical plates and

control the horizontal position of the beam. External electric circuits are used to control and

change the amount of charge on these plates and the electric field between them. The

electron beam passes between each pair of plates, and is attracted to the positively charged

side and repelled by the negatively charged side. In this way, the plates control the path of the

electron beam and where the beam hits the screen. The fluorescent screen is the display on

the bulb. The most common material used on the display is phosphorous, and it is painted on

the inside of the bulb. Electrons emerging from the deflection plates strike the screen and the

phosphorous converts the energy in the electron beam into photons of visible light. This

result in a spot of light on the display, with brightness proportional to the intensity of the

beam. The element on the screen is also phosphorescent, meaning that it emits energy as light

gradually instead of instantaneously. This allows us to see lines on the screen instead of a


4/6

moving dot. This line is maintained by rapid, repetitive tracing. In an operating cycle, the

heater gives electrons in the cathode enough energy to escape. The electrons are attracted to

the accelerating anode and pulled through a control grid that regulates the number of

electrons in the beam, a focusing anode that controls the width ofthe beam, and the

accelerating anode itself. The vertical and hori ontal deflection plates create electric fields

that bend the beam of electrons. The electrons finally hitthe fluorescent screen, which

absorbs the energy from the electron beam and emits itin the form oflightto display an

image atthe end ofthe glass tube.

Meanwhile, capacitors also use the electric field in its operation. When a capacitoris

connected across a source of voltage, such as a battery, itis charged by a particular amount,

depending on the voltage and the value of capacitance because oftheE F(electromotive

force) ofthe battery, negative charges flow to the lower plate, leaving the upper plate

positively charged. Along with the growth of charge, the electric field is also building up. The

flux lines are directed from the positive to the negative charges and at right angles to the

plates. When the capacitoris fully charged, the voltage ofthe capacitoris equalto the voltage

ofthe source and opposite in polarity. The charged capacitor stores the energy in the form of

an electric field. It can be said that an electric field indicates voltage.

Ifthe two plates ofthe capacitor are spread farther apart, the electric field must curve to meet

the plates at right angles. The straightlines in view diagram become arc and approximately

semicircle where the plates are in a straightline. Instead of flat metal plates, as in the

capacitor, the two elements can take the form of metal rods or wires and form the basic

antenna.


5/6

Besides that, Photostat machi eis widely used in business, education, and

government. There have been many predictions that photocopiers will eventually become

obsolete as information workers continue to increase their digital document creation and

distribution, and rely less on distributing actual pieces of paper. Its is operating through

Xerography. The process of xerography is widely used for making photocopies of printed

materials. The basic idea behind the process was developed by Chester Carlson who was

granted a patent for his invention in 1947.Some features ofthe xerographic process involve

simple concepts from electric fields and optics. Firstly, the surface of a plate or drum is

coated with a thin film ofthe photo conductive materials which is usually selenium. The

photo conductive surface is given a positive electrostatic charge in the dark. The page or

paper materials copied are then projected on to the charged surface. The photo conducting

surface becomes conducting only in areas where light strikes. There the light produces charge

carrierin the photo conductor which neutrali e the positively charged surface. The charges

remain on those areas ofthe photo conductor not exposed to the light. Then, itleaves a

hidden image ofthe objectin the form of a positive surface charge. Next, a powder called

Toneris negatively charged and dusted onto the photo conducting surface. The charged

powder adheres only to the areas that contains positively charged image. Atthis point, the

image becomes visible. Itis then transferred to the surface of a sheet of positively charged

paper. Finally, the toneris fixed to the surface ofthe paper by heat. This results in a

permanent copy ofthe original. Therefore, electric field is very importantto human beings

as well as to operate the devices and machines.


6/6

REFERENCE

1) BOOKS - Physics Fifth edition (ABBOTT)Physics ( Key Ideas)

2) INTERNET - www.ac.wwu.edu/~vawter/PhysicsNet/Topics/Capacitorswww.tpub.com/neets/book10/3

Documents

Physics Assingment ( Electric Field)