Powerpoint Presentation about Electricity: Resistance and some Laws of Physics

1. Resistance

3. Recap:
 Last time we have tackled about electricity . Again… A
type of energy fueled by the transfer of electrons from
positive and negative points within a conductor.
 Electricity is widely used for
providing power to buildings, electric devices, and even
some automobiles…
 Electricity is very harmful to humans because of high
voltage it contains but electricity can be lessened by the
use of Resistors with different resistance…

4. Resistance
 Resistance of an object to the flow of
electrical current.
 R = V/I
 Resistance equals the ratio of voltage to
current.
 Unit: Ohm ( Ω )
 An object of uniform cross section has a
resistance proportional to
its resistivity and length and inversely
proportional to its cross-sectional area.

5. Georg Ohm and
Ohm’s Law
Georg Simon Ohm (1789 - 1854) first investigated the
relationship between the current in an electric circuit
element and the electrical potential difference, often
called voltage, across the circuit element.
Ohm's Law
For a circuit or circuit element, Ohm's law mathematically
relates the current, the voltage, and the electrical
resistance. The voltage is more properly called the
electrical potential difference, but voltage is often used
because it is less of a mouthful.
Ohm found that in a circuit the voltage and current are
directly proportional to each other. That means if the
current, I, in a circuit is plotted along the horizontal, or x,
axis and the voltage, V, is plotted along the vertical, or y,
axis, then the result will be a straight line. The slope of
this line is the resistance, R, of the circuit.

6. Resistors
A resistor is a two-terminal electronic
component that produces a voltage across its
terminals that is proportional to the electric
current through it in accordance with Ohm's
law:
V = IR
Resistors are elements of electrical networks
and are ubiquitous in most electronic
equipment. Practical resistors can be made of
various compounds and films, as well as
resistance wire. The primary characteristics of
a resistor are the resistance, the tolerance, the
maximum working voltage and the power
rating.

7. Conductors
A conductor is a material which contains
movable electric charges. In metallic conductors, such
as copper or aluminum, the movable charged particles
are electrons. Positive charges may also be mobile in
the form of atoms in a lattice that are missing
electrons (known as holes), or in the form
of ions, such as in the electrolyte of a battery.
Insulators are non-conducting materials with fewer
mobile charges, which resist the flow of electric
current.
All conductors contain electric charges which will
move when an electric potential difference (measured
in volts) is applied across separate points on the
material. This flow of charge (measured in amperes)
is what is meant by electric current. In most
materials, the direct current is proportional to the
voltage (as determined by Ohm's law), provided the
temperature remains constant and the material
remains in the same shape and state.

9. In Metals
A metal consists of a lattice of atoms, each
with a shell of electrons. This is also known as a
positive ionic lattice. The outer electrons are
free to dissociate from their parent atoms and
travel through the lattice, creating a 'sea' of
electrons, making the metal a conductor. When
an electrical potential difference (a voltage) is
applied across the metal, the electrons drift
from one end of the conductor to the other under

10. In Insulators
In metals, the Fermi level lies in the
conduction band giving rise to free conduction
electrons. However, in semiconductors the
position of the Fermi level is within the band
gap, approximately half-way between the
conduction band minimum and valence band
maximum for intrinsic (semiconductors. This
means that at 0 kelvins, there are no free
conduction electrons and the resistance is
infinite. However, the resistance will continue

11. In liquids/electrolytes
In electrolytes, electrical conduction
happens not by band electrons or holes, but by
full atomic species (ions) traveling, each
carrying an electrical charge. The resistivity of
ionic liquids varies tremendously by the
concentration - while distilled water is almost
an insulator, salt water is a very efficient
electrical conductor. In biological membranes,
currents are carried by ionic salts. Small holes

13. Difference between an Alternating
Current and Direct Current
Alternating Current Direct Current
In alternating Direct current (DC) is
current (AC) the the undirectional flow
movement of electric of electric charge.
charge periodically reverses The electric charge flows in
direction. AC is the form in a constant direction,
which electric power is distinguishing it
delivered to businesses and from alternating current
residences. The usual (AC).
waveform of an AC
power circuit is a sine wave.

14. The First Direct Current
Electricity is a very different energy source than
heat or light. In nature, electricity only rarely occurs,
in some animals or with lightning. In the search to
create electrical energy, scientists discovered that
electrical and magnetic fields are related. A magnetic
field near a wire causes electrons to flow in a single
direction along the wire because they are repelled
and attracted by the north or south poles. Thus, DC
power from a battery was born, primarily attributed
to Thomas Edison's work and promotion.

15. Thank You!!! 