 Draw
a picture of a SERIES Circuit. Show
a battery, a switch, and a light bulb in
your drawing.
 Draw
a picture of a PARALLEL Circuit.
Show a battery, a switch, and TWO light
bulbs in your drawing.
 Be
prepared to discuss your pictures.
Ohm’s
Law
The
law stating that the
direct current flowing in a
conductor is directly
proportional to the potential
difference between its ends.
Ohm’s Law
 What
happens to the Resistance when the
Current is doubled and the Voltage stays
the same?
 The
Resistance is halved!
 What
will happen to the Voltage when the
Resistance is tripled and the Current
remains constant?
 The Voltage
is Tripled too!
 What
happens to the Current when the
Resistance is reduced by 1/3 and the
Voltage stays the same?
 The
Current is Tripled!
Measuring Current
Current is measured in units of amperes (A)
•
2A
2A
2A
2A
1A
2A
1A
In a series circuit,
current is the same
at all the points
In a parallel circuit,
current is shared
between all the points
What is the current?
3A
3A
4A
1A
4A
1A
4A
1A
SERIES CIRCUIT
PARALLEL CIRCUIT
Measuring Voltage
• Voltage – the electrical push that a
cell/battery gives to the current
• Voltage is also known as Potential
Difference
•
Voltage is measured in units of volts (V)
Measuring Voltage
3V
3V
3V
1.5V
1.5V
In a series circuit,
voltage is shared
between all the points
3V
In a parallel circuit,
voltage is the same at
all the points
What is the current and voltage?
6V
4A
A
4A
3V
V
3V
V
A
4A
Current
Series
Same
Parallel Shared
Voltage
Shared
Same
What is the current and voltage?
4A
6V
A
4A
V
6V
A
2A
V
6V
A
2A
Measuring Resistance
•
Resistance – slows down current, adding
components to a circuit increases resistance
•
Resistance is measured in units of ohms (Ω)
•
More resistance = Less current = Less light
In a series circuit, add up all resistance to get the total.
 Use
the OHM’s Law Equation to answer this
question:
 What
happens to the Resistance when the
Current is tripled and the Voltage stays the
same?
 Use
the OHM’s Law Equation to answer
this question:
 What
happens to the Voltage when the
Resistance is reduced by 1/2 and the
Current stays the same?
 Electric
power is the rate, per unit time,
at which electrical energy is transferred
by an electric circuit.
 The
SI unit of power is the watt [W], one
joule per second, [ J/s].
 Electric
power is usually produced by
electric generators, but can also be
supplied by sources such as electric
batteries.
Electrical Power
How much voltage gives 5 amps of
current through a 3 Ω light bulb?
I = V/R
V = (5A)  (3Ω)
V = 15V
How much current flows in a
circuit with a 1.5 volt battery
and three 1 ohm resistances
(bulbs) in series?
I = V/R
I = (1.5V) / (3Ω)
I = .5A
What is the voltage drop
across each resistor in the
circuit?
In a series
circuit,
voltage is
shared
between all
the points
9V/3 = 3V
A light bulb with a resistance of
1.5Ω is connected to a 1.5V battery
in the circuit. Calculate the power
used by the light bulb?
P = IV
I = V/R
I = (1.5V) / (1.5Ω)
I = 1A
P = (1A)  (1.5V) = 1.5 W
P = 1.5 W