Meter Reading
 Reading
a meter is generally very
easy. Identify if you are reading volts,
amperes or ohms.
 Then identify if there is a range or a
multiplier
 Use the correct scale when reading
 Ammeter and Voltmeters are read
from left to right
 Ohm meters are read from right to left
and compress in the higher values
Meter Reading
 What
are the three quantities a
meters read?
- Volts
- Amperes
- Ohms
Basic Circuit
 What
are the three basic parts of a
circuit?
Sorry we’re closed
 What
is the difference between an
open and a closed circuit?
Sorry we’re closed
 How
much resistance exists in an
open circuit?
 In
a closed circuit?
 Resistance depends on the
resistance of the components in the
circuit.
Ohm’s Law States
 There
is a relationship between
voltage current and resistance in a
circuit.
 That current is directly proportional to
voltage and inversely proportional to
resistance.
 Meaning when voltage increases so
does current, when resistance
increases current decreases.
Series Circuits
Remember
that current stays the
same in this circuit.
Voltage changes (drops) across
resistors and loads.
Resistance is the sum of the resistors.
Formula
What
is the formula for Ohm’s Law?
E= I x R
If we know 2 quantities we can
solve for the unknown.
Remember we MUST be in base
units.
Formulas
Applying Ohm’s Law: Series
 What
do you know about series
circuits?
 In a series circuit, the same current (I)
flows throughout the circuit
 And total voltage is equal to the
voltage drop across the individual
loads (resistance)
 Total resistance is equal to the sum of
the resistances
Parallel Circuits
 What
do you know about parallel
circuits?
 Remember that voltage stays the
same in a parallel circuit.
 Current changes through each
branch of the parallel portion.
 Total resistance is always lower than
the lowest resistor in parallel.
Applying Ohm’s Law: Parallel
 In
a parallel circuit the same voltage is
applied to each branch in the circuit
 And total current is equal to the sum of
the individual branch currents
 Resistance is equal to the sum of the
reciprocals of the individual branches
Steps to Applying Ohm’s Law
 1.
Draw the schematic and label
the known quantities
 Solve the equivalent circuits and
redraw as series
 Solve for the unknowns
Kirchhoff’s Current Law
The total current into a junction is equal to
the total current out of the junction.
Kirchhoff’s Voltage Law
The sum of all the voltage drops in a
circuit will equal the voltage source
(voltage rise)
Total E – E1 – E2 – E3 = 0
Total E = E1 + E2 + E3
These both say the same thing
Applying Ohm’s Law
 What
is the total current flow below?
 Total Current = ?
 Total Voltage = 12Volts
 Total Resistance = ?
 R1 = 560 ohms
 R2 = 680 ohms
 R3 = 1KΩ
Applying Ohm’s Law
 How
much voltage is dropped across
resistor R2 in a series circuit?
 Total
Current = ?
 Total Voltage = 48Volts
 Total Resistance = ?
 R1 = 1.2 KΩ
 R2 = 3.9 KΩ
 R3 = 5.6 KΩ
 Explain
Power
 Electrical Power is defined as the rate at
which energy is converted. For
example, current flow through a lamp
converts energy into light and heat. The
rate at which that energy is converted is
Power
 Power is represented by Watts (W)
What is the formula for Power?
P=VxI
What does it mean to use a
meter in series or parallel?
Which meter(s) are used in
series?
Which meter(s) are used in
parallel?
What is an Ammeter used for?
Is it used in Series or in parallel?