Download 10.08 series circuit

Name _____________________________
Series Circuits Lab
Adapted from Science Joy Wagon
Purpose: To investigate the behavior of electricity in a series circuit (a circuit with only a single
current path). We wish to examine some rules regarding current (I) and electric potential
difference (V) {a.k.a.- potential, potential drop, or voltage}.
Materials: two light bulbs – round and long (resistors), one rechargeable cell or DC power source,
an ammeter, a voltmeter, 6 alligator clips and 6 wires.
Procedure 1: Determine the resistance of each of your bulbs. Using the DC power source with the
built in Ammeter and Voltmeter, determine the resistance of each bulb.
Bulb Sketch
Data
Resistance
Bulb 1= Resistor 1
Voltage =
Current =
Bulb 2 = Resistor 2
Voltage =
Current =
Procedure:
1. Set up the circuit shown in diagram l but do not connect to the positive tab of
the + cell (battery) until you are ready to take a reading. (Although we are using
variable resistors in this circuit, we are using them as fixed resistors. We will not
be changing their resistances.)
Caution: With labs involving the ammeters, start with them on the highest scale
and move to lower scales only when the readings will fall within the particular
range of the scale. If either the ammeter's or the voltmeter's needle moves to the
left or shoots off the scale to the right, then quickly disconnect one end of the
cell and recheck your circuit. If you are using a DC power source, set the
voltage at 1.5 – 4 V depending on the bulb and turn the current knob
completely to the right. If you have questions, ask your teacher.
2. Record the current in the circuit as measured by the ammeter in diagram 1
then proceed to rearrange your circuit to look like diagram 2, then diagram 3,
each time recording the current measured by the ammeter at each location in the
circuit.
Arrangement of circuit
Diagram 1
Diagram 2
Diagram 3
Current measured by the ammeter
3. Based on your measurements of current at various places within a series circuit what could you
Name _____________________________
conclude about the behavior of electrical current within a series circuit?
4. Set up the circuit in diagram 4. Draw on diagram 4 how you would have to attach the voltmeter
to measure the total potential of the cell while it's in the circuit (call it V T). Remember that
voltmeters measure the potential difference between the two leads of the meter, so the meter must
be wired across (in parallel) the object to be measured, not in line (in series) with it. Use the
voltmeter to measure VT and record the value both on the diagram at the appropriate location and
in the table provided for you.
5. Using diagram 4, continue to draw in how you would connect the voltmeter to measure the
potential drop across resistor one (R1). Use your voltmeter to actually measure the potential drop
(VR1) across this resistor and record this value on the diagram and in the table.
6. Using diagram 4, continue to draw in how you would connect the voltmeter to measure the
potential drop across resistor two (R2). Use your voltmeter to actually measure the potential drop
(VR2) across this resistor and record this value on the diagram and in the table.
7. Now use Ohm's law to calculate the total resistance (RT) of the circuit, the resistance of R1 and
the resistance of R2 and place these values in the table.
Name _____________________________
Current through ...
(from step 3)
Potential differences
Resistance
(using Ohm's law)
Total
(for the entire circuit)
VT=
IT=
RT=
Of R1
VR1=
IR =
R1=
Of R2
VR2=
IR2=
R2=
8. From the data and calculations in your table, try to make a generalization about how the total
resistance relates to the resistances of the individual parts. Describe this relationship in the space
below.
9. From the data and calculations in your table, try to make a generalization about how the total
voltage relates to the potential drops of the individual parts. Describe this relationship in the space
below.
Problems (It is sometimes helpful to draw the circuit to understand what the problem is asking)
1. A 10 , a 15 , and a 5  resistor are connected in series across a 90 V battery. Find the
total resistance of the circuit. What is the current through each resistor?
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2. A 20  and a 30  resistor are connected in series across a 110 V potential difference.
What is the total resistance of the circuit? What is the current through each resistor? What
is the voltage drop across each resistor?
3. A 60 , a 90 , and an unknown resistor are connected in series across a 130 V battery.
An ammeter in the circuit reads 0.67 A. What is the total resistance of the circuit? What is
the size of the unknown resistor? What is the power dissipated in each resistor?
Complete Problems 4-6 on a separate sheet of paper. Make sure your drawings are neat.
4. A circuit consists of a 5  and a 10  resistor in series across a 45 V battery. A voltmeter
is connected across each resistor. An ammeter measures total current. A switch is also
included. Calculate the total current and the voltage drops across each resistor. Draw the
circuit.
5. Three resistors, a 5 , a 10 , and a 15 , are connected in series. Each has a voltmeter. A
switch and an ammeter are included, as well as a 30 V battery. What does the ammeter
read? What is the voltmeter reading across the 10  resistor? Draw the circuit.
6. What is the total resistance and the voltage drop, V? What is the power dissipated in the 6
 resistor? What is the electrical energy used by the 6  resistor in 20 seconds? What is
the magnitude of R?
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1. What is the total resistance and the voltage drop, V, across the 6  resistor. What is the
power dissipated in the 4  resistor? What is the electrical energy used by the 4  resistor
in 10 sec? What is the magnitude of R?
2. What is the magnitude of R?