ELECTRICITY
PHYSICS I
ELECTRIC POTENTIAL
• The electric potential - is the amount of work energy needed
to move a unit of electric charge from a reference point to
the specific point in an electric field with negligible
acceleration of the test charge to avoid producing kinetic
energy or radiation by test charge.
VOLTAGE
• Definition: Voltage is the electric potential difference.
where:
Voltmeter – a device used to measure voltage.
TAKE NOTE:
The basic difference between electric potential and electric
potential energy is that Electric potential at a point in an electric
field is the amount of work done to bring the unit positive charge
from infinity to that point, while electric potential energy is the
energy that is needed to move a charge against the electric field
EXAMPLES:
• The work done by the electric force as the test charge (q0 = + 2.0 x10^-6 C)
moves from A to B is (Wab = +5.0 x10^-5 J. (a) Find the value of the difference,
(deltaPE = PEb - PEa), in the electric potential energies of the charge between
these points. (b) Determine the potential difference, (deltaV = Vb – Va), between
the points.
• Suppose an electron is accelerated from rest through a potential difference Vb –
Va = Vba = +5000V (a) What is the change in electric potential energy of the
electron? What is (b) the kinetic energy, and (c) the speed of the electron ( m =
9.1 x 10^-31 kg) as a result of this acceleration?
ELECTROMOTIVE FORCE AND CURRENT
• The maximum potential difference is called the electromotive force*
(emf) of the Battery. In a typical car battery, the chemical reaction
maintains the potential of the positive terminal at a maximum of 12 volts
(12 joules/coulomb) higher than the potential of the negative terminal, so
the emf is 12 V. Thus, one coulomb of charge emerging from the battery
and entering a circuit has at most 12 joules of energy.
ELECTRIC CURRENT
• Current flows through a circuit when a source of power is
applied. It is the amount of electrons flowing through an
electrical circuit measures in Amperes (A).
• An ampere is number of electrons passing a given point in
one second.
ELECTRIC CURRENT AND CHARGE
FORMULA:
TYPES OF ELECTRIC CURRENT
• Alternating Current (AC) – is a current that reverses its
direction of flow at regular intervals. Alternating current flows
in any circuit connected to a power supply producing an AC
Voltage.
• Direct Current (DC) – is current that flows in only one
direction. Direct current flows in any circuit connected to a
power supply producing a DC voltage.
CURRENT FLOW
• Conventional current flow – is current flow from positive to
negative.
• Electron current flow – is current flow from negative to
positive.
ELECTRICAL RESISTANCE
• Resistance - is a measure of the opposition to current flow
in an electrical circuit. Resistance is measured in ohms,
symbolized by the Greek letter omega (Ω).
• Resistor – A device that provides pure resistance in the
circuit.
HOW TO READ RESISTORS
HOW TO READ RESISTORS
HOW TO MEASURE RESISTORS USING
MULTIMETER
CLOSED, OPEN AND SHORT CIRCUIT
OHM’S LAW
• The relationship between Voltage (V), Current (I), and
Resistance (R) is what we call as Ohm’s Law
ILLUSTRATION OF OHM’S LAW
POWER IN ELECTRIC CIRCUITS
• Power – is the rate of doing work or using energy.
• Formula:
EXAMPLES:
• A current of 3.8 A flows in a wire for 12 minutes. (a) How much charge
passes through any point in this circuit during this time? (b) How
many electrons would this represent?
• A 12V battery is connected to a light bulb and draws 150mA of
current. (a) What is the electrical resistance of the light bulb? (b) How
much power does it consume? (c) How much will it cost to operate
this bulb for a month if the cost of electricity is 0.11pesos/kWh?
• A 12.5 Coulombs of charge flows through a 5kilo-ohms resistor in 8
minutes. (a) What is the electric current flows through the resistor?
(b) How much power is consumed by the resistor? (c) Find the voltage
across the resistor.
