Essay on Electricity: Electric Charge and Physics Electricity

Submitted By Felissen
Words: 1544
Pages: 7
Open Document
ME0005 – Foundations of Physics

Electricity 1/4

Current and Charge
All familiar with electric circuits: lighting, computers, mobile phones etc
A current is a flow of charged particles
Scientific convention: current flows from positive (+ve) to negative (-ve)  conventional current
What is flowing?
In a metal wire there are free electrons that can move about  conduction electrons  they allow a metal to conduct an electric current
Electrons are negatively charged. When an electron breaks away from an atom in the metal, it leaves behind a positively charged ion. There are an equal number of electrons and ions in a metal  the metal is charge neutral When a battery or ‘cell’ is connected, its ‘voltage’ provides a push to make the conduction electrons flow around the circuit. The negatively charged electrons flow to the positive terminal of the cell (opposite to conventional current) Current flows at all points in the circuit once the circuit is completed. Electrons are already present in the metal and do not flow from the cell
Electrical current is measured in amperes (A). How much charge is moving when a current of 1 A flows? Depends on how long the current has been flowing: charge = current  time

ME0005 – Foundations of Physics

Electricity 1/4

Charge is measured in coulombs (C). We define the coulomb as:
One coulomb is the amount of charge which moves past a point when a current of 1 ampere flows for 1 second
We can say:

Q = I t
If a current, I, flows for an amount of time t, the charge that moves during that time is Q
An electron has a charge of -1.6  10-19 C, represented by the symbol eExample:

If a current of 10 A flows through a lamp for
1 hour, how much charge moves through the lamp in this time?
Q =
=
=
=

Example:

I t
10  (60  60)
10  3600
36000 C

A car battery labelled ‘50 A h’ can supply
50 A for 1 hour. How long can the battery supply 200 A needed to start the car?

First we need to find the total charge in the battery:
Q =
I t
=
50  (60  60)
=
180000 C
Now we can find the time the battery can supply 200 A:
t

=

Q
I

=
=

180000 / 200
900 s

ME0005 – Foundations of Physics

Electricity 1/4

Resistance
What determines ‘how much’ current flows?
 voltage, V, of the cell:
 more voltage = more current
 resistance, R, of the component:
 greater resistance = smaller current
The resistance of a component tells you how much voltage is needed to push a given current though it.
We can say:

current 

voltage resistance I

V
R

Resistance is measured in ohms ()
Example:

A car headlamp has a resistance of 36 .
What current flows when it is connected to the car’s 12 V battery?

I

V
R

=
=

12 / 36
0.33 A

Re-arranging the equation for R we have: R 

V
I

We then define resistance as:
The resistance of a component in a circuit is the ratio of the voltage across the component to the current in it
So, one ohm is one volt per ampere:

1  = 1 VA-1

ME0005 – Foundations of Physics

Electricity 1/4

Measuring resistance
To measure resistance we need to know I and V
We use an ammeter to measure current: connected in series to measure the current passing through a component We use a voltmeter to measure voltage: connected in parallel to measure the voltage across a component
Varying the voltage and measuring the current we obtain an:
I / V characteristic graph
The gradient of the graph is the resistance (R = V/I)

V

voltage

A

current

For a metallic conductor we get a straight line that passes through the origin (no voltage applied, no current flows).
We say that:


the current that flows through the conductor is proportional to the voltage across it

Components with an I / V graph like this are called ohmic conductors and are said to obey:
Ohm’s Law  For a conductor at constant temperature, the current in the
Show More

Related Documents: Essay on Electricity: Electric Charge and Physics Electricity

Essay about Organic Solar Cell

will allow every household in Australia to generate their own electricity, affordably and sustainably. • This invention advances current technology by creating solar cells that can be applied as flexible plastic coatings and even paints that harvest the sun’s energy across large areas to generate electricity. Who owns the intellectual property? • Professor Paul Dastoor was the inventor and he is a Professor of Physics at the University of Newcastle in Australia. Video • http://www…

Words 880 - Pages 4

Research Paper On The World Communicates

Year 11 Physics – Research Task The World Communicates Currently, many governments around the world are experimenting with integrating GPS technology into unmanned aerial vehicle. There has also been research conducted to integrate GPS technology into navigation assistance devices for the visually impaired and blind people. Self-driving cars are also being developed that use GPS technology to avoid collision and drive themselves through busy streets. GPS technology in remote sensing and mapping…

Words 972 - Pages 4

Photoelectric Effect Essay

3 Doping & Band structure: 3 The p-n junction 5 The photoelectric effect in photocells: 6 Applications of the photoelectric effect in photocells: 6 Current research: 8 Impact on society and the environment of solar cells: 8 Impact of advances in physics on scientific thinking & technology 9 Bibliography: 10 This report aims to gather and summarise information on the: use of the photoelectric effect in photocells Effect of light on semiconductors in solar cells Throughout this report a general understanding…

Words 2777 - Pages 12

Electric Vehicle and Regenerative Braking Systems Essay

or fed back into a power system for use by other vehicles. Electrical regenerative brakes in electric railway vehicles feed the generated electricity back into the supply system. In battery electric and hybrid electric vehicles the energy is stored in a battery or bank of capacitors for later use. Figure 1 (Regenerative brakes in a car) As the figure indicates the axle is coupled with the electric motor mechanically and the motor is connected to the battery (The blue arrows in the figure denote…

Words 1810 - Pages 8

Quantum Mechanics and Pop Ch Essay

Poetry of Physics and the Physics of Poetry Instructor: Prof. Robert K. Logan Text: Poetry of Physics and Physics of Poetry – Robert K. Logan – World Scientific THE APPROACH TO OUR STUDY OF PHYSICS IN THE The basic concepts of physics are described in simple non-mathematical and non-technical language. The beauty of the ideas, namely, the poetry of physics, is presented. A short history of development of the ideas will be given so that students can relate to the ideas of physics that we…

Words 793 - Pages 4

Fundamental Forces Essay

paragraph 6 http://sciencepark.etacude.com/particle/forces.php) So it means that the larger body, the stronger the force. But on the scale of individual particles, the force is extremely small, only in the order of times that of the strong force. In physics, gravitational acceleration is the acceleration on an object caused by force of gravitation. Neglecting friction such as air resistance, all small bodies accelerate in a gravitational field at the same rate relative to the center of mass. (From paragraph…

Words 1025 - Pages 5

Scien: Electricity and Circuit Essay

ceAn ammeter measures electric current, in amps, by measuring how much charge is flowing in the circuit. A voltmeter measures, in volts, the difference in electrical energy between two points of a circuit. Have you ever heard a crackle when taking off your jumper? This is caused by tiny electric charges on your clothes. It's called static electricity. Your jumper and shirt get electrically charged as they rub together, and then negative electric charges jump from one to the other. This makes…

Words 1229 - Pages 5

World of Chemistry Essay

undergraduate course his favourite subjects were Greek and mathematics; but after his graduation in 1891 he took, for two years, a teaching post in elementary physics. It was during this period that he developed his interest in the subject in which he was later to excel. In 1893, after obtaining his mastership in physics, he was appointed Fellow in Physics at…

Words 2329 - Pages 10

Essays: Double Positive Charge

Nuclear Physics and Radioactivity Atomic Number – No. of Protons in Nucleus of Atom Mass Number – Total No. of Protons and Neutrons in the Nucleus Isotopes – Atoms have the same No. of Protons but different No. of Neutrons * Same Chemical Properties * Different Physical properties Radio Isotopes – Unstable atoms that are radio active * An individual radioactive isotope is known as a Radioisotope Artificial Transmutation – Creates artificial radioisotopes * Uses the process…

Words 1240 - Pages 5

Vn Phys Stuff Essay examples

PHYSICS NOTES Space 2 Gravitational Acceleration 2 Projectile Motion and Galileo’s Analysis 2 Escape Velocity 3 Gravitational Potential Energy and Escape Velocity 3 Blast-off: Forces at work during rocket launches 3 Circular Motion 3 Satellites and Newton’s Law of Universal Gravitation 4 Deep-Space Probes 4 Communication Between Earth and Satellites 4 Re-entry Into the Earth’s Atmosphere 5 Limitations of Current Space Travel…

Words 3539 - Pages 15