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Accuracy is how close a measured value is to the actual (true) value.
Precision is how close the measured values are to each other.
Keakuratandarisistempengukuranadalahderajatkedekatandaripeng
ukurankuantitasuntuknilaisebenarnya (true).
Kepresisiandarisistempengukuran,
jugadisebutreproduktifitasataupengulangan,
adalahsejauhmanapengukuranulangdalamkondisitidakberubah,
menunjukkanhasil yang sama.
Kesalahan
•
Kesalahandarialatukurdinyatakandalam
• M–T=ε
– T : nilaisebenarnyadaribesaran yang diukur
– M : harga yang didapatdaripengukuran
– ε : kesalahandarialatukur
Hasilbagidarikesalahanthphargasebenarnya (ε/T) :
kesalahanrelatifataudisebutrasiokesalahan (dalam %)
Koreksidilambangkandengan (α), dimanaα = T - M
α/M disebutkoreksirelatif / ratio koreksidalam (%)
Contoharusdenganhargasebenarnya 25,0 A dandiukurdenganhargaukur 24,3 A
Berapakesalahan, koreksi , rasiokesalahan, rasiokoreksi : ?
Pemilihanalatukuruntukkepentinganpengukuran,
atauperencanaandalampenggunaanperalatandiklasifikasikandalam
4
golongansesuaidaerahpemakaiannya, yaitu : 1. Alat-alatukurdarikelas 0,05; 0,1; 0,2
alatukurinitermasukgolonganalatukurdenganketelitianataupresisi yang tertinggi.
Biasanyaditempatkansecara
stationer
didalamlaboratorium,
dandipergunakanuntukeksperimen-eksperimen
yang
memerlukanpresisi
yang
tinggiataupadapengujianalatukur yang lainnya.
Alatukurkelas 0,5 ;
alatukurinimempunyaiketelitiandanpresisipadatingkatberikutnyadarikelas 0,2,
biasanyadipergunakanuntukpengukuran-pengukuranpresisi.
Alatukurkelas 1,0;
alatukurinimempunyaiketelitiandanpresisipadatingkatlebihrendahdarialatukurkelas 0,5,
biasanyadipergunakanpadaalatukur portable yang kecilataualat-alatukur yang
ditempatkanpada panel yang besar.
Alat-alatukurdarikelas 1,5; 2,5; dan 5; alatukurinidipergunakanpada panel-panel
dimanaketelitiansertapresisidarialatukurtersebuttidakbegitupenting.
• Setiapalatukurlistrikmempunyaikelastersendiri.
Kelassuatualatukurlistrikmenunjukkanbesarnyakesalahanpengukuranalatt
ersebut.
• Semakinkecilkelassuatualatukurlistrik,
makakesalahanpengukurannyaakansemakinkecil.
• StandarIEC mengklasifikasikandalam 8 kelas, yaitukelas : 0,05; 0,1; 0,2; 0,5;
1;
1,5;
2,5;
dan
5.
Hal
tersebutdimaksudkanbahwakesalahandarialatukurtersebutmasing- masing
± 0,05 %; ± 0,1 %; ± 0,2 %; ± 0,5 %; ± 1 %; ± 1,5 %; ± 2,5 %; dan ± 5 %.
• MisalnyaVoltmeter mempunyaikelas 1, hasilpengukurannyamenunjuk 9
Volt, berartihasilpengukurannyaberadaantara:
9 Volt - (1% x 9 Volt) sampai 9 Volt + (1% x 9 volt),
atauantara 8,91 Volt sampai 9,09 Volt.
Contoh
• Alatukurkelas 1 denganskalamaksimal 3 A, menunjukkanangka 0.6 A
dimanahargasebenarnyaadalah 0.62 A
• Berapabesarkesalahannya :
• Kesalahanrelatifnya (terhadpaphargapenunjukan) :
• Kesalahanrelatifterhadaphargaskalamaksimal:
• Sebab-sebabkesalahan
Standard deviasi (σ)
•
•
Deviation just means how far from the normal
it is the square root of the Variance
Jarum penunjuk
Ko
Poros
Inti besi lunak
Kumparan putar
magnet
EAS-PBL/DTE/FTUI
KOM
Ørsted's Compass
• In 1820, a Dane by the name of Hans Christian Ørsted discovered the relationship between
electricity and magnetism in a very simple experiment that is shown in the below tutorial.
One evening, as Ørsted was setting up materials for a lecture, he brought a compass close to
a live electrical wire, and observed that the needle on the compass jumped and pointed to
the wire. More experimentation showed that a circular magnetic field surrounded a currentcarrying wire. Ørsted had proved that electricity and magnetism were connected and the
study of electromagnetism was born.
•
•
The equipment in the tutorial models Ørsted's 1820 apparatus. The battery is a voltaic pile
constructed of copper and zinc plates in a dilute acid solution. A copper wire is held in place
by wooden clamps. Because the battery is not connected, the compass needle points north,
attracted solely by the Earth's magnetic field.
Click the Turn On button to connect the battery and create an electric current in the wire,
which travels from the positive to the negative terminals. When the current flows through
the wire, the compass needle aligns itself with the magnetic field created by the electrons
traveling in the current, rather than with the Earth’s magnetic field. Because the magnetic
field travels around the wire in a circle (see our Magnetic Field of a Wire tutorial), the
compass will point in different directions depending on where it’s placed. If you hit the Flip
Battery button to reverse the direction of the current in this tutorial, the magnetic field
around the wire will reverse direction, too, as will the compass needle.
Whenever current travels through a conductor, a magnetic field is
generated, a fact famously stumbled upon by Hans Christian Ørsted
around 1820. Depending on the shape of the conductor, the contour of
the magnetic field will vary. If the conductor is a wire. The magnetic
field is strongest in the area closest to the wire, and its direction
depends upon the direction of the current that produces the field, as
illustrated in this applet.
Presented in the tutorial is a straight wire with a current flowing
through it. Plus and minus signs indicate the poles of the battery (not
shown) to which the wire is connected. The conventional direction of
current flow is indicated with a large, black arrow. (As convention
dictates, the current flow opposes the actual direction of the
electrons, illustrated in yellow). The magnetic field lines generated
around the wire due to the presence of the current are depicted in
blue. To observe the direction of the field at any given point around
the circumference of the wire, click and drag the compass needle, (its
north pole red, its south pole blue). The direction of the magnetic field
around the wire is also indicated by the small arrows featured on the
individual field lines. Click the Reverse button to change the direction
of the current flow and observe the effect this change exerts on the
wire’s magnetic field.
There is a simple method of determining the direction of the magnetic
field generated around a current-carrying wire commonly called the
right hand rule. According to this rule, if the thumb of the right hand is
pointed in the direction of the conventional current, the direction that
the rest of the fingers need to curl in order to make a fist (or to wrap
around the wire in question) is the direction of the magnetic field.
14 August 1777 – 9 March 1851
The equipment in the tutorial
models Ørsted's 1820 apparatus
Ørsted had proved that electricity
and magnetism were connected
and
the
study
of
electromagnetism was born.
http://www.magnet.fsu.edu/educ
ation/tutorials/java/oersted/index.
html
A charged particle moving through a magnetic field
experiences a force that is at right angles to both the
direction in which the particle is moving and the
direction of the applied field. This force, known as the
Lorentz force, develops due to the interaction of the
applied magnetic field and the magnetic field generated
by the particle in motion. The phenomenon is named for
Dutch physicist Hendrik Lorentz, who developed an
equation that mathematically relates the force to the
velocity and charge of the particle and the strength of
the applied magnetic field.
You can predict which way the wire will move by using the left-hand rule. You need to
contort your hand in a bit of an unnatural position for this rule: If your index finger points
in the direction of a magnetic field, and your middle finger, at a 90 degree angle to your
index, points in the direction of electrical current, then your extended thumb (forming an
L with your index) points in the direction of the Lorentz force exerted upon that particle,
and the direction in which the wire shifts in the tutorial.