Analysis of the Earth and Environment Lecture 13: Electricity & Magnetism Flashcards
List the four fundamental forces and describe their strength levels
Gravitational force: The weakest force but it has infinite range.
▪ Electromagnetic Force: It has an infinite range and is much stronger than gravity.
▪ Strong nuclear force: The strongest force but it only acts over short range
▪ Weak nuclear force: Weaker than the strong and
electromagnetic force but stronger than gravity.
Define Static electricity
Static electrical charge is created when insulators ( or conductors
insulated from Earth) are subjected to friction.
* There are two types of static electrical charge positive charge and
negative charge.
The sort of charge acquired depends on the material of the rod and the cloth. E.g. a polythene rod rubbed with a cloth acquires a negative charge
Define a conductor
an atom that can pass and exchange electrons in its valence shell
True or false:
Opposite charges (Positive and a Negative) are attracted to each other
and Similar charges (e.g. two positive charges) are repelled by one another.
True
Opposite charges attract
Similar charges repell
Define and explain an induced charge
A charge that is created on an object by a nearby charged object.
If a positively charged rod is brought near to a piece of paper, the paper sticks to the rod.
As the positively charged rod approaches the paper, the electrons in the paper are attracted towards the rod.
making one side of the paper negative and one side
positive. A charge has been induced on the paper
Define a field line/pattern
Any two charged bodies exerts equal and opposite forces on each other without being directly in contact.
* The path a free positive test charge follows is called a Line of force or Field Line.
Convention:
The field lines are given a direction away from a
positive charge and towards a negative charge.
Field lines never cross each other.
Define Coulombs law and the equation
If two objects have charges (q1&q2) and are separated by a certain distance (r2), the coulomic/electrical force between these two objects is K (Coulombs constant) multiplied by q1 x q2 divided by the r2
q1 q2 F = K --------------
r2
F = electric force
K = coulombs constant
q1 & q2 = Charges
r2 = Distance between charges
Define potential difference
The difference of electrical potential between two points.
If an electrical current flows,it does so because of a
difference in electrical potential.
* Electrical current flows from points at a higher potential to points at a lower potential
- In a conventional battery or cell,the action of the chemicals inside causes its two terminals to beat two different electrical potentials;known as positive (+ve) and negative(–ve)
Define Current and the equation
A current is a flow of charged of particles and is measured in Amperes
Charge
Current = ————– or I = Q/T
Time
Current, I measured in Amperes
Charge,Q measured in Coulombs
Describe the two types of current
Direct current
flow of charged of particles is constant
Alternating current
Current has fluctuations, flow of charged of particles is not constant
Define resistance/conduction
A conductor will try to impede the flow of a current
(unless it’s a superconductor).
- The resistance of a conductor is defined by the
equation:
Voltage
Resistance = ————- or R=V/C
Current - Ohm’s Law
The unit of resistance is the Ohm ( Ω )
Describe Resistivity and its relationship with the length of the conductor
Electrical resistance of a conductor of unit cross-sectional area and unit length
If we double the length of the conductor we double its resistance. Resistance is related to the resistivity (a property of the material itself).
Electron collisions with the metal lattice are the cause of resistance. As temperature goes up,
resistance goes up.
Give the equation for Resistance
R = ρ L/A
R= resistance (Ω)
L= length of conductor (m)
A= cross sectional area of conductor (m2)
ρ = resistivity of the material (Ω.m)
How fast do electrons drift?
Electrons drift at about 1mmper second. They don’t travel at the speed of light!
- Electron collisions with the metal lattice are the cause of resistance. As temperature goes up, resistance goes up.
What is the equation for Ohms law
V = IR
V = Voltage
I = Current
R = Resistance
Power (watt) = voltage (volt)current (amp)
or
P = V x I = I2R (since V = IR)
Describe the units used for electricity
1 Watt is one joule of energy per second
A joule is equal to the energy dissipated as heat when an electric current of one ampere passes through a conductor with a resistance of one ohm for one second
kW or kW hours as DEpractical measures of power or
power used.
Describe the discovery of magnetism
Magnetic Phenomena first observed at least 2500 years ago in fragments
of magnetized iron ore found near the ancient city of Magnesia(now Manisa ,in western Turkey). These fragments are examples of permanent
magnets.
Define a permanent magnet
A magnet that retains its magnetic properties in the absence of an inducing field or current.
Iron, Nickel & Cobalt are the only elements capable of being permanent magnets.
Various alloys are also used, and some crystalline materials but all containing the above elements in their structure.
In addition to mechanical stimulation of the metal
‘needles’into alignment,they can be ‘frozen’ in place if heated in the presence of a strong magnet. - Generates new permanent magnet.
Define The Tesla and Magnetic flux
SI unit of magnetic flux density
1 Tesla = 10,000 Gauss (Old Unit)
The number of magnetic field lines passing through a given closed surface.
The strongest continuousmagnetic field yet
producedin alaboratory 45T.
* The strongest (pulsed) magnetic field ever
obtained (with explosives) in a laboratory 2800T.
* On a neutron star 10 power of 6 T to 10 power of 8T
Describe the relationship between electrics and magnets
Current I flowing in a long,straight
wire generated a magnetic field,also
denoted as a B-field.
* The relationship between the current
and field direction is often summarized
via the Right-Hand-Rule
* The relationship between the strength
of the B-field (magnetic field strength),
current and measurement distance r is
given by:
Describe the three basic Magnetic materials
Ferromagnetic substances
Paramagnetic substances
Diamagnetic substances
Describe Ferromagnetic substances
Ferromagnetic substances - Strongly magnetised in the same direction as the applied magnetic field
Examples are iron, cobalt and nickel.
These are the substances we normally think of as being“magnetic”.If we heat up a ferromagnetic material it will lose its magnetism and become paramagnetic.
Describe Paramagnetic substances
Weakly magnetised in the same direction as the applied magnetic field.
Examples are oxygen, magnesium and aluminium
Paramagnetic material is only weakly attracted to a magnetic field and loses its magnetism once the field is gone.
Paramagnetic materials have randomly oriented magnetic moments
Describe Diamagnetic substances
Weakly magnetised in a direction opposite to the applied magnetic field.
Examples are hydrogen, nitrogen and Sodium.
Describe Earths magnetic field
Weakly magnetised in the same direction as the applied magnetic field.
Examples are oxygen, magnesium and aluminium:
Describe the geomagnetic flip
Also known as magnetic reversal - mean the process by which the North pole is transformed into a South pole and the South pole becomes a North pole.
It could cause a disrupt of communications systems and power grids.
