1

DC Circuits

Name ________________________________________ Date_______ Period ____

A

.

Ohm’s Law

1

. Construct a circuit consisting of a battery, an ammeter, and a resistor. Vary the

voltage and record the current measure

d

by the ammet

er in the table below.

Trial

Voltage (Volts)

Current (Amps)

Trial

Voltage (Volts)

Current (Amps)

1

7

2

8

3

9

4

10

5

1

1

6

12

2

. Draw a graph of voltage versus current.

(Note: Your axes label may be different

.

)

(a)

What type o

f relationship exists between the voltage and the current?

(b)

Determine the slope of your graph.

Slope of

graph _________________

(c)

What is the value of the resistor used in your circuit?

R = _________________

(d)

How does the slope of your graph compare with

the value of the resistor in your

circuit?

2

B

.

Resistors in Series

1.

Construct a circuit consisting of a battery

, an ammeter, and 3 resistors having

different resistance values

(R

1

, R

2

, and R

3

)

.

Connect all circuit elements in

series.

Draw a circuit diagr

am of your circuit.

2.

Set the terminal (battery voltage) at a

fixed

value for this part of the investigation.

a.

With the ammeter connected between the + terminal of the battery and the

first resistor in the circuit, measure the current. Record this as I

t

(the

total

current in the circuit).

b.

Remove the ammeter and connect it between the first

(R

1

)

and the second

(R

2

)

resistors in the circuit. This is the current through R

1

. Record this

value for I

1

in the table

.

c.

Next, connect the ammeter between resistors R

2

a

nd R

3

to measure the

current I

2

through resistor R

2

.

Record this current for I

2

in the table.

d.

Finally, connect the ammeter between R

3

and the negative terminal of the

battery to measure the current I

3

through resistor R

3

.

Record I

3

.

3.

Repeat step 2 above fo

r

two more

set

s

of three different resistors R

1

, R

2

, and R

3

.

Record your data in the table below.

Record the battery voltage as V

t

.

I

t

=

I

1

=

I

2

=

I

3

=

Trial

R

1

R

2

R

3

R

1

+ R

2

+ R

3

V

t

/ I

t

1

2

3

Trial

V

1

V

2

V

3

V

1

+ V

2

+ V

3

V

t

1

2

3

Questions

:

1.

What can conclude about the current through each resistor?

2.

What is the relationship between the sum of the voltage drops across the

resistors and the battery voltage?

3.

Is it possible to replace the three resistors by one resi

stor such that the

total current, I

t

,

remains the same? If possible, what should the value of

this resistor be?

3

C.

Resistors in Parallel

1.

Construct a circuit consisting of a battery, an ammeter, and 3 resistors having

different resistance values (R

1

, R

2

, and R

3

). Connect all circuit elements in

parallel. Draw a circuit diagram of your circuit.

2.

Set the terminal (battery voltage) at a

fixed

value for this part of the investigation.

a.

With the ammeter connected to the

+ terminal of the battery and the

junct

ion between the first and second resistors in the circuit, measure the

current. Record this as I

t

(the total current in the circuit).

b.

Remove the ammeter and connect it in the first branch containing only R

1

in the circuit. This is the current through R

1

.

Record this value for I

1

in the

table

.

c.

Next, connect the ammeter in the second branch containing resistor R

2

to

measure the current I

2

through resistor R

2

.

d.

Finally, connect

in the branch containing resistor

R

3

to measure the current

I

3

through resistor R

3

.

e.

Use the voltmeter to measure the voltage drop across each resistor.

3.

Repeat step 2 above for

two more

set

s

of three different resistors R

1

, R

2

, and R

3

.

Record your data in the table below. Record the battery voltage as V

t

.

V

1

=

V

2

=

V

3

=

V

t

=

Trial

R

1

R

2

R

3

V

t

/ I

t

1

2

3

Trial

I

1

I

2

I

3

I

1

+

I

2

+

I

3

I

t

1

2

3

Questions

:

4.

What can

you

conclude about the

voltage drop across

each resistor?

5.

What is the relationship between the

total current and

the currents through

the individual resistors

?

6.

Is it possible to replace the three resistors by one resistor such that the

total current, I

t

,

remains the same? If possible, what should the value of

this resistor be?

4

Ser

ies Circuit Diagram

:

Parallel Circuit Diagram

:

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