Microsoft Word - Lab 4_316_2021.docx
Lab Section # 4
Circuit Diagrams
&
Ammeter-Voltmeter
Part I
4A-Circuit Diagrams
Here are some common circuit symbols. In
the lab this semester, you will only need to
deal with about one fifth of these. Don't
panic if they look strange or you don't know
what a resistor or a capacitor is B you are in
the right place.
Part 1 (take Home lab):
Note: You will need these wires, battery holder, batteries, light bulbs for the next lab!!!!
A) Resistors in parallel and series
Grocery List
Breadboard
multimeter
3 resistors
hook up wires
attery, 3 V attached with your set or two 1.5V batteries
You may need cardboard box, aluminum foil, and a potato
Put two AA batteries together.
You may build a battery holder or tape batteries together (though it will be hard) or
use device with equipment for 3 V that comes with
eadboard.
(If you need to build a battery holder, there is movie on youtube at the beginning)
https:
www.youtube.com/watch?v=_GI1gWBXNrw&t=5s
Check the voltage of your battery ________________
1)Measuring resistance
You may safely measure the resistance of your own body by holding one probe tip with the
fingers of one hand, and the other probe tip with the fingers of the other hand. You have a high
esistance across your body, Note: be very careful with the probes, as they are often sharpened to
a needle-point. Hold the probe tips along their length, not at the very point! You may need to
adjust the meter range again after measuring the 10 kΩ resistor, as your body resistance tends to
e greater than 10,000 ohms hand-to-hand. Try wetting your fingers with water and re-measuring
esistance with the meter. What impact does this have on the indication? Try wetting your fingers
with saltwater prepared using the glass of water and table salt, and re-measuring resistance. What
impact does this have on your body's resistance as measured by the meter?
Resistance is the measure of friction to electron flow through an object. The less resistance there
is between two points, the harder it is for electrons to move (flow) between those two points.
Given that electric shock is caused by a large flow of electrons through a person's body, and
increased body resistance acts as a safeguard by making it more difficult for electrons to flow
through us, what can we ascertain about electrical safety from the resistance readings obtained
with wet fingers? Does water increase or decrease shock hazard to people?
Measure resistances of different objects as well as try some vegetables or fruits.
I used a lemon? You may use anything else like potato.
Resistance of different objects
You also have to measure three resistors
object Resistance Comments
Human body
Human body (wet)
Aluminum foil
Resistor 1
Resistor 2
Resistor 3
lemon
Extra pts: built a potato battery, show set up picture and explain physics behind it.
You now can measure voltage and cu
ent of your circuit.
Put the smallest resistor in the
eadboard and connect to the battery
Measure voltage without isolating the components. Voltage is the easiest thing to
measure with a multimeter. To measure a cu
ent you must put the meter in the
circuit, which means cutting a wire to insert the meter. Measuring voltage is as
easy as placing the meter probes at two points and reading the meter that indicates
the voltage difference between the two points.
2) Measuring voltage and cu
ent
Create similar circuit:
Record Voltage ___________________
Create this circuit:
Record cu
ent____________
Calculate your resistance____________
Compare it with your measured value of the resistor________________
3) Series circuit.
Create a series circuit like this with your resistors
Make a set up as shown in picture
Make a picture of your set up and add it with your lab report
Measure voltage drop around any of the resistors ____________
Measure cu
ent around any resistor_______________
Calculate resistance based on Ohms Law ____________
The % difference between measured and calculated one _________
Measure total resistance like this setup:
Total resistance measured __________
Total resistance calculated __________
The % difference___________
4) Parallel circuit
Set up a parallel circuit
Take a picture of your set up and add it to your lab report
Check voltage drop around any resistor____
Cu
ent around any resistor____________
Calculate resistance for that resistor based on Ohms law _______
The % difference_________
Measure total resistance of the circuit________
Calculate total resistance of the circuit___________
The % difference______________
You are next suppose to measure your total resistance similar to this:
Part II (STREAM LAB)
Equipment that will be used:
Galvanometer
Decade Box Resistors; (In your labs it will be used for R0 and R1
)
C. Single Pole Knife Switch (S); shown here the switch is in the
Closed position, meaning that the circuit loop in which this inserted will be completed, so
electricity (electrical cu
ent) will flow.
4B-Ammeters and Voltmeters
Purpose:
To study the physical principles involved in the design of DC voltmeters and DC ammeters.
Apparatus:
A DC galvanometer, resistance boxes, a power supply, copper wire, a laboratory digital
voltmeter, potentiometer.
Theory:
The galvanometer is the heart of a DC voltmeter and DC ammeter. The galvanometer is in fact a
sensitive ammeter, i.e., it is an instrument which will measure a cu
ent in the range of
microamperes. The purpose of this experiment is to show how much an instrument can be used to
construct an ammeter and voltmeter.
The DC galvanometer, as shown on the right, consists of a coil of wire placed in the magnetic field
of a permanent magnet. When a cu
ent flows through this coil, the magnetic field produced will
tend to align itself with the magnetic field of the permanent magnet. For a given coil and a given
permanent magnet the torque produced will depend on the cu
ent in the coil and on the angle
etween the magnetic field of the permanent magnet and the plane of the coil. The manufacturers
of galvanometers usually try to eliminate the angle factor so that the torque will depend only on
the cu
ent. A measurement of the torque will then constitute a measurement of cu
ent. The
measurement of torque is accomplished by a
anging for a counter torque to be developed as the
coil rotates. One of the ways of producing his counter torque is to attach a small coil spring to the
axis of the cu
ent coil. As the axis rotates the coil spring tries to prevent this rotation. The counter
torque is designed to be proportional to the angle the axis has been rotated. In this way, the angle
through which the coil rotates measures the cu
ent in the galvanometer. The angle is read on a
scale marked off in amps, or ma.
One needs to know some of the characteristics of a galvanometer before it is possible to proceed
successfully in the construction of voltmeters and ammeters. In particular, one needs to know the
esistance of the galvanometer and the maximum cu
ent that is allowable for the galvanometer.
A third characteristic which is usually assumed but which is important is that the deflection is
directly proportional to the cu
ent passing through the galvanometer. If high precision were
equired then this characteristic would need to be checked.
To determine the galvanometer resistance we will use
Half deflection method.
The galvanometer is connected in series with a high resistance so
that the cu
ent does not exceed the maximum cu
ent. By
connecting a known resistance in parallel with the galvanometer
the cu
ent through the galvanometer will