Download Series Circuits

Series Circuits
Circuits
• Lets compare . . . Circuits with mountain streams
• No matter which path the stream takes down the
mountain, the change in elevation is the same
• Some rivers flow in a single stream, some flow in
multiple paths
• No matter how many paths, the amount of water
going down the mountain stays the same
• The amount of water flowing in the river is
similar to current in an electrical circuit
• The elevation the river drops is similar to
potential difference (voltage)
• The width of the path the water takes is
similar to resistance
Series Circuits
Have one
current
pathway
Predict
1. Using one battery, light one bulb.
2. Make observations about the bulbs brightness.
3. Add a 2nd bulb into the circuit. Make sure you have only
one path between battery terminals. Use only one battery.
4. Make observations about the brightness of each bulb.
Q1: What quantity have you changed by adding another bulb
to the circuit?
Q2: Based on your knowledge of Ohm’s Law, how does this
change the current?
Resistance
• By adding a second bulb, you have
increased the total resistance in the circuit.
• Equivalent resistance is the sum of all the
resistors in a circuit.
• Can also be stated as the value of a single
resistor that could replace all resistors in a
circuit and not change the current
Calculating Resistance
Rtotal  R1  R2  R3
Predict
1. Predict what will happen to the bulbs if
you add another battery.
2. Add another battery to the circuit.
3. Make observations.
Q3: What quantity have you changed by
adding another battery to the circuit?
Q4: How does this effect the current?
Concept Check
• Adding voltage increases the current in the
circuit
• Resistors act like speed bumps . . . Current
slows down through each resistor.
• If resistors are added to a circuit and
voltage stays the same, the current
decreases.
Measuring Current
• Current is measured in Amps with an
Ammeter.
• Ammeters are placed in series with the
load.
Predict
1. Add an ammeter to the circuit.
2. Observe the ammeter reading.
3. Predict what will happen to the current in the
circuit if you add another bulb.
4. Add a 3rd bulb to the circuit.
5. Make observation about the current reading on
the ammeter and the brightness of the bulbs.
Concept Check
Q5: What can you conclude about
current in a series circuit?
• Current in a series circuit is the same
through each resistor
• Each bulb has the same brightness.
Predict
1. Predict what you think will happen to the
brightness of the bulbs if you unscrew bulb
number 3?
2. Unscrew bulb #3. What happens?
Q6: Why does this happen?
Concept Check
• Series circuits have only one pathway.
• If the path is cut off, the current does not
flow.
• Current is determined by knowing the total
voltage in the circuit and the total
resistance in the circuit.
Voltage in a Series Circuit
• Voltage in each resistor can be measured
using a voltmeter.
• A voltmeter is connected to each side of a
resistor.
Predict
• The voltage source for your circuit is the
battery.
Q7: How much voltage is in your circuit?
• Predict the value of voltage through each
bulb. Explain your prediction.
Measuring Voltage
• Place the voltmeter in the circuit around bulb #1.
Record the voltage reading.
• Move the voltmeter to bulb #2. Record the voltage
reading.
• Move the voltmeter to bulb #3. Record the voltage
reading.
Q8: What can you conclude about the voltage in
each bulb as compared to the total voltage in the
circuit?
VOLTAGE in series
• Voltage changes in a series circuit as
resistors are added.
• This change is called a voltage drop.
• The total voltage drop in a circuit is the sum
of the individual voltage drop through each
resistor.
• The net change in voltage is zero.
• The battery generates the same amount of
energy that is used by the bulbs.
Calculating Voltage
Vtotal  IR1  IR2  IR3
OR
V  I ( R1  R2  R3 )
V1  IR1
V2  IR2
V3  IR3
Example 1
Find the following:
IT
_____
I1
_____
R1 _____
V2 _____
V3 _____
VT _____
Example 2
A 10Ω, 15 Ω and 25 Ω resistor are connected
in a series circuit with a 100 V battery. What
is the equivalent resistance in the circuit?
What is the current in the circuit?
Rtotal  R1  R2  R3
Rtotal  10  15  25  50