PASCO EM-8812 User Manual

Instruction Manual with

Experiment Guide and

Teachers’ Notes

Resistance Apparatus

EM-8812

012-09573A

Resistance Apparatus Table of Contents

Contents

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Wires . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Voltage Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Current Supply and Measurement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Four-wire Measurement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Apparatus Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Measurement Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Fuse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Stacking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

About the Experiments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Experiment 1: Exploratory Study of Resistance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Experiment 2: Resistance versus Length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Experiment 3: Voltage versus Length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Teachers’ Notes and Typical Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Technical Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Resistance Apparatus

EM-8812

Included Equipment Part Number

Resistance Apparatus EM-8812

Two sets of wire (8 wires per set) in storage tube EM-8813

Fuses (one installed and one spare), 2 A mini-blade 530-045

Other Equipment Recommended

Voltage measurement:

Galvanometer Sensor

Multimeter SE-9786A

PS-2160

or similar

Current measurement:

Galvanometer Sensor

Multimeter SE-9786A

current meter of power supply

1, 2

Power Supply (capable of at least 1 A) PI-9877

PS-2160

or similar

SE-9720A

Patch Cords (4mm banana plug) SE-7123

Sensor requires a PASPORT interface such as Xplorer GLX (PS-2002).

Two Galvanometer sensors can be used simultaneously to measure voltage and current. Second sensor

requires a multi-port interface or two single-por t interfaces.

Introduction

In the Resistance Apparatus, a current is established in a wire of known diameter, and the voltage drop across a section of the wire is measured. Students can calculate the resistance of the wire and the resistivity of the material.

Resistance Apparatus Wires

Wires

The set of wires included with the apparatus contains two of each sample. Place one of each sample in the storage trough on the apparatus for immediate use and set the others aside as spares to replace lost or damaged wires. Order part EM-8813 for a new set of replacements with two of each wire.

The set includes wires of five different materials with the same diameter, and four different diameters of the same material (brass). Refer to the table to identify the wires.

Approximate

Attracted

Material Color

Copper Red No 1.8 ± 0.1 0.040 2

Aluminum Light gray No 4.9 ± 0.1 0.040 2

Brass Yellow No 7.0 ± 0.5 0.020, 0.032, 0.040, and 0.050 2

Nichrome Dark gray No 105 ± 5 0.040 0.5

Stainless Steel Dark gray Yes 79 ± 1 0.040 1

All samples are alloys. The actual resistivity of a sample depends on its composition.

Excess constant current will cause wires to heat up, changing their resistivities. Current up to 2 A can be applied briefly to

all wires.

to magnet?

Resistivity

(µΩ·cm)

Diameter(s)

(inches)

Maximum

Voltage Measurement

Measure the voltage drop along the wire with a model PS-2160 Galvanometer Sensor or a multimeter with a resolution of 0.1 mV or better. The maximum voltage measured will be less than 1 V.

Current Supply and Measurement

Constant

Current

(A)

Current is established in the wire by an external power supply. Select a power supply capable of at least 1 A at 1 V. The apparatus contains a 2 A fuse to protect against excessive current (see page 6 for fuse replacement instructions). If you are using a current-regulated power supply capable of more than 2 A (such as model SE-9720A), set the current regulation to 2 A before connecting it to the apparatus. The apparatus contains a series resistance of 0.5 Ω, which makes it easier to tune the current through the wire by changing the applied voltage.

To measure current you can use a model PS-2115 V/I Sensor or a multimeter. If you are using a power supply with an accurate built-in current meter (such as model PI-9877), a separate meter is not necessary.

Four-wire Measurement

In the apparatus, the resistance of a length of wire is determined by applying a known current and measuring the voltage. This technique is known as a four-wire measurement. (The “four wires” are the two leads through which current is applied and the two leads of the voltmeter.) The voltage is measured only across the part of the wire under test (excluding the power supply leads), and virtually no current flows through the voltmeter leads (so there is no voltage drop in them). This technique allows a very

Model No. EM-8812 Apparatus Setup

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small resistance to be measured even if the resistances of the four measurement wires are much higher, unknown, or variable.

Apparatus Setup

Wire Installation

1. Move the reference and slider probes to the extreme left and right positions so

they are parked on the ramps that will hold them out off the wire.

Wire clamps

Alignment lines

Insert wire here

Alignment

lines

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Sliders in parked possitions

2. Loosen the wire clamps.

3. Insert the wire through the clamps and under the probes, as shown in the dia-

gram. Observe the alignment lines marked near the wire clamps and note that the wire goes through the front of the left-hand clamp and through the back of the right-hand clamp. (This configuration causes the wire to be pulled tight when the clamps are closed.)

4. Tighten both clamps enough to secure the wire in place.

5. To remove the wire, park the probes and loosen the clamps.

External Device Connections

To power supply

Current

1. Power Supply: Set

the voltage of the power supply to zero.

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Connect it to the power jacks of the apparatus (see diagram) so that the current will flow from right to left through the wire.

To voltmeter or galvanometer

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2. Current Measurement: If you plan to use a current sensor or meter, connect it

in series with the apparatus.

3. Voltage Measurement: Connect Galvanometer Sensor or voltmeter to the jacks

on the reference probe (-) and slider probe (+).

Resistance Apparatus Measurement Procedure

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Measurement Procedure

1. Turn on the power

supply and adjust the applied voltage to

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established the desired current (I) through the wire.

2. Place the reference

probe on the “0 cm” mark.

3. Move the slider probe

Reference probe

on 0 cm mark

to any point on the wire. Read the length ( ) in centimeters from the scale on the apparatus. This is the length of wire over which the voltage is measured.

4. Read the voltage (V).

In a typical experiment, you would make several measurements of V while varying one other parameter (such as I, , the wire diameter, or the wire material).

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Slider probe

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Fuse

If current greater than 2 A is applied to the apparatus, the fuse will open and require replacement. The fuse is located on the underside of the apparatus. To remove it, pull it straight out. The apparatus includes a spare fuse taped to the underside.

The fuse is an 2 A mini-blade fuse, which can be purchased at automotive supply stores.

Fuse

Stacking

To stack two or more apparatuses for storage, turn the clamp screws to be “horizontal” (as illustrated). Push the reference probe to the right as far as it will go (a little to the right of the “0 cm” mark) and push the slider probe to anywhere left of the “24 cm” mark.

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About the Experiments

The experiments in the manual represent three examples of how the apparatus can be used, ranging from a simple exploratory lab (Experiment 1) to more advanced (Experiment 3). Teachers’ notes and sample data for all three experiments appear on page 15–17.

Experiments 2 and 3 refer to specific power supplies, sensors, and software; however variations of these experiments can be done with equipment available in most physics teaching labs.

Spare fuse

Screws horizontal

for stacking

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Probes pushed

toward center

+ 12 hidden pages