# ch 13 makeup lab circuit

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7 Οκτ 2013 (πριν από 4 χρόνια και 7 μήνες)

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Ohm's Law and Series Circuits

http://www.article19.com/shockwave/oz.htm

Name _____________________________________ Hour _____

Lab Objectives:

1.

Measure voltages and current in a series circuit.

2.

Find t
he resistance of a resistor in a series circuit without
measuring its resistance directly.

3.

Find the total resistance of a series circuit.

Series Circuits facts:

a.

The current is the same in all parts of a DC circuit when
resistors and loads are connected i
n series with the voltage
source.

b.

In DC circuits with resistors or loads in series, the voltage drop
across each resistor or load depends on the resistance of each

c.

Total resistance (Rtot) in a series DC circuit is the sum of the
individ
ual resistances (R
tot

= R
1

+ R
2

+ R
3

+ …)

d.

For any resistor, given the current through it and the voltage
across it, you can use Ohm's law to find the resistance.

Ohm's Law: Since there is only one current path in a series circuit, there's only
one value
of current flow. Current flow value is determined by the voltage
source and the total resistance in the circuit. According to Ohm's law, the
current is

I =

V / 剥

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2. Connect the three selected resistors in series with a switch, battery and
wires.
Turn Pop
-
ups off
.

3. Place the ammeter in the circuit in several different locations and
measure the total current in the circuit. Record the value below.

Measured Circuit Current = I = _______ amperes

4. Use the voltmeter to measure the voltage source (battery). Record t
he
total voltage below.

Source Voltage = _____________ volts

5. Calculate the circuit current using Ohm's law and the data recorded in
steps #1 and #4 above:

Calculated Circuit Current =
Circuit Voltage

/
Circuit Resistance

I
tot

= Vs / R
tot

=

_______
amper
es

6. Use the voltmeter to measure the voltage across each resistor. Record
your values in column 3 in the table below.

Data Table #1

Resistor #

Value of
Resistance from
Pop
-
ups

Measured value
of Voltage across
Resistor

Calculated Value
of Resistance

R1

= V
1

R2

= V
2

R3

= V
3

Column Totals

R
tot
=


= V
tot

R
tot

=


Using Ohm's law calculate the resistance of each resistor and record it in
Column #4 of Data Table #1. The formula to use is:

R =

V / I

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-

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Does the measured source voltage equal the sum of
the voltage drops
across each resistor recorded in the data table?

3.

Does the total resistance of the circuit equal the sum of the resistors
placed in the circuit? (R
tot

= R
1

+ R
2

+ R
3
)

4.

How are ways the voltmeter and ammeter placed in the circuit different
?
(Which is placed in series and which is in parallel to the component to be
measured? Which will have all the current flowing into it?)

Research the following:

5.

Why do electrical resistors have colored bands across them?

6.

What is the name given to a circu
it that has a load or resistance total or
0.0 ohms?

Lab Procedure Part 2

Repeat the above experiment using three lamps to replace the resistors. The
lamps are loads with a resistance value

1. Use your internet browser and open the web site listed above.

C
lick on the "pop
-
ups" button in the lower left
-
hand corner of the screen.
Use the pop
-
up feature to determine the resistance value of the three
lamps.
Their total resistance should be less than 1000 ohms
. Record their
individual resistance value in column
#2 of Data table #2.

Total Resistance = ________ ohms

2. Connect the three selected lamps in series with a switch, battery and
wires.
Turn Pop
-
ups off
.

3. Place the ammeter in the circuit in several different locations and
measure the total current in the
circuit. Record the value below.

Measured Circuit Current = I = _______ amperes

4. Use the voltmeter to measure the voltage source (battery). Record the
total voltage below.

Source Voltage = _____________ volts

5. Calculate the circuit current using Ohm's
law and the data recorded in
steps #1 and #4 above:

Calculated Circuit Current = Circuit Voltage

/
Circuit Resistance

I
tot

= Vs / R
tot

=

_______
amperes

6. Use the voltmeter to measure the voltage across each lamp. Record your
values in column 3 in the tab
le below.

Data Table #2

Resistor #

Value of
Resistance from
Pop
-
ups

Measured value
of Voltage across
Resistor

Calculated Value
of Resistance

Lamp 1

= V
1

Lamp2

= V
2

Lamp 3

= V
3

Column Totals

R
tot

=


= V
tot

R
tot
=


Using Ohm's law calculat
e the resistance of each lamp and record it in
Column #4 of Data Table #2. The formula to use is:

R =

V / I

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Wrap
-

Compare the results of the lamps in series to the resistors in series. Do
lamps and resistors affect current the same way in a DC series circuit?

Try This
:

1.

Remove one lamp from the circuit and replace it with a wire. What
changes occur
in the circuit's total resistance, total current, and total
voltage?