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Lab: DC Circuits – Resistors in Series

Theory: Circuits are said to be in series when they are joined, as in the figure below, so that the

current flows without change from one piece to the next.

For resistors connected in series:

1. The total potential difference for a group of resistors in series is equal to the sum of

the potential drop across the individual resistors:

V

T

= V

1

+ V

2

+ V

3

+ …

2. The current in every part of the circuit is the same:

I

T

= I

1

= I

2

= I

3 …

3. The equivalent resistance of the series group is equal to the sum of each individual

resistance:

R

eq

= R

1

+ R

2

+ R

3

…

Objective: To study the relationships among resistance, voltage, and current when resistors are

connected in a series circuit.

Materials needed: D.C. power supply, resistance board, D.C ammeter, digital multimeter,

connecting wire, switch

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Procedure:

1. Connect one end of the switch to the power supply and the other end to resistor D. Connect

resistors D and E in series. Connect resistor E to the ammeter and finally continue back to

the power supply. Measure the total current with the ammeter.

I

T

= _____________________ A

How much current is running through resistor D?

How much current is running through resistor E?

Explain your previous two answers. Why is the total current the same as the current

through each resistor?

A

To measure total current

Source

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2. Measure the voltage drop across each resistor (V

E

, V

D

) and the total voltage drop across the

group of resistors, V

T.

V

E

= __________________ V

V

D

= __________________ V

V

T

= __________________ V

V

To measure the voltage around resistor E

To measure the voltage around resistor D

To measure the total voltage

V

V

4

3. Using V

T

and I

T

as determined in steps 1 and 2, calculate the total (effective) resistance, R

T

.

R

eq

= V

T

/ I

T

= _____________ ohms

4. Calculate the value of each resistance:

R

E

= V

E

/ I

E

= ___________________ ohms

R

D

= V

D

/ I

D

= ___________________ ohms

5. Ask Mr. Cozzolino for the ACTUAL resistance of each resistor. Calculate the percent

error for the resistance of each resistor and the equivalent resistance.

% Error = [(Accepted value – Measured value) / Accepted value] x 100

Practice

1. The diagram represents a series circuit containing three resistors. What is the current

through resistor R

2

?

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