E031
MASSACHUSETTS INSTITUTE OF TECHNOLOGY
Department of Physics
8.02
Experiment 3: Ohm’s Law & DC Circuits
OBJECTIVES
1.
To explore the measurement of voltage & current in circuits
2.
To see Ohm’s law in action for resistors
3.
To learn how to translate circuit diagrams to physical circuits on a board
PRELAB READING
INTRODUCTION
When a battery is connected to a circuit consisting of wires and other circuit elements
like resistors and capacitors,
voltages can develop across those elements and currents can
flow through them.
In this lab we will investigate simple circuits with only resistors in
them.
We will confirm that there is a linear relationship between current through and
potential difference across resistors (Ohm’s law:
V
=
IR
).
The Details:
Measuring Voltage and Current
Imagine you wish to measure the voltage drop across and current through a resistor in a
circuit.
To do so, you would use a voltmeter and an ammeter – similar devices that
measure the amount of current flowing in one lead, through the device, and out the other
lead.
But they have an important difference.
An ammeter has a very low resistance, so
when placed in series with the resistor, the current measured is not significantly affected
(Fig. 1a).
A voltmeter, on the other hand, has a very high resistance, so when placed in
parallel with the resistor (thus seeing the same voltage drop) it will draw only a very
small amount of current (which it can convert to voltage using Ohm’s Law
V
R
= V
meter
=
I
meter
R
meter
), and again will not appreciably change the circuit (Fig. 1b).
Figure 1:
Measuring current and voltage in a simple circuit.
To measure current
through
the resistor (a) the ammeter is placed in series with it.
To measure the voltage
drop
across
the resistor (b) the voltmeter is placed in parallel with it.
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 Fall '10
 DOURMASHKIN
 Current, Magnetism, Mass, Resistor, ohm, Electrical resistance

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