Transcript 3. Measuring Electricity

Electrical Potential (Voltage)
Answers (Page 303)
1. a) Why is it necessary for the electrons to
move continuously around the circuit?
b) From which terminal do the electric
charges flow into the circuit? Explain.
2. a) Define the term “electrical potential”?
b) State the SI unit and the name the
symbol used for electrical potential
3. Why is it possible to measure an electrical
potential across the terminals of a dry cell,
even if the electrons are not flowing into
the circuit?
Measuring Electricity
Electric Potential – the electrical
energy that an electron possesses.
Electric current is a measure of the
rate at which the electric charges
move past a given point in a circuit.
Ampere (A) is the S.I. unit used to
measure electric current.
Ex: In a 100 w light bulb only 1A of
current flows through it.
Voltage – electric potential
Volts (V) – the S.I. unit used to
measure electric potential.
Voltage Drop – a measure of the
energy each electron gives up as it
moves through a circuit. (Commonly
used for potential difference.)
Electrical Resistance
Resistance – is the ability to hold back
the flow of electrons in a conductor.
The molecules found in every type of
conductor resists the flow of electrons
to some extent.
Resistors – are electrical devices that are
used in circuits that are designed to resist
the flow of electricity. The symbol for
electrical resistance is “R” and the S.I. unit
is the Ohm ().
Ex: the resistance of a 100 W light bulb is
about 144 .
When electrons flow through a
conductor the electrical resistance
causes a loss of electric potential
(voltage). There is a “difference” in the
amount of electric potential after the
electrons have flowed through the
conductor. This difference is referred
to as the potential difference.
Ohm’s Law
Ohm’s Law: The potential
difference between two
points on a conductor is
proportional (directly related)
to the electric current
flowing through the
conductor.
Potential
Difference
(Voltage Drop)
= Electric Current x Electrical Resistance
V=IxR
Potential difference (V) is measured in volts (V)
Electric Current (I) is measured in ampere (A)
Resistance (R) is measured in ohms ()
Ohm’s Law Questions
Sample Problems:
1. What is the voltage drop across the
tungsten filament in a 100 watt light
bulb? The resistance of the filament is
144 ohms and a current of 0.833
amperes is flowing through it.
I = 0.833 A
R = 144 OHMS
V=?V
V=IXR
V = (0.833A)(144Ω)
V = 120 V
The voltage drop across a 100 watt light bulb is
120 V.
2. An electric toaster is connected to a 120
V outlet in the kitchen. If the heating
element in the toaster has a resistance of
14 Ohms. Calculate the current flowing
through it.
V = 120 V
I=?A
R = 14 OHMS
V=IXR
120 V = I X (14 Ω)
120V = I
14 Ω
I = 8.6 A
The current flowing through the toaster is 8.6
A.