Tip 1: How to find the charge capacitor

in engineering and physical problems are sometimes required to find charge capacitor .Direct measurement charge and capacitor - rather laborious task.Therefore, in practice used more affordable ways of finding charge and capacitor .
you need
  • capacitor voltmeter
To find charge capacitor , connected to a DC voltage, multiply the capacity capacitor on the voltage,ieuse the formula:
Q = UC, where:
Q - charge capacitor , in coulombs,
U - the voltage source voltage, in volts,
C - capacity capacitor , in farads.
Note that the above formula determines the amount of the charge a fully charged capacitor .But as charge ka capacitor happening fast enough in practice use of this particular pattern.
power supply voltage can be measured by a voltmeter.To do this, switch the mode to measure the DC voltage terminals and connect the device to a voltage source.Record readings in volts.
Learn capacity capacitor can read marks on his body.Note that t
he unit capacity farad (F) - very big, so in practice is rarely used.To denote the capacitors used smaller units.It microfarads (uF), which is equal to one millionth of Faraday and PF (PF), which is equal to one millionth of a microfarad.
1 uF = 10-6 F, 1 pF = 10-12 F.
sometimes used and the intermediate unit of capacity - Nanofarad equal to one billionth of a Farad.
1 nF = 10-9 F.
If the condenser is small, its capacity is indicated by symbols.Read
marking capacitor , drawing attention to his tsvet.Esli the capacitor specified just two digits, it is its capacity in picofarads.
For example, the inscription "60" will mean the capacity of 60 pF.
If the capacitor contains one uppercase letters or numbers, you find in the table below the corresponding numeric znachenieA 1.0 I 1.8 R 3.3 Y 5.6
B 1.1 J 2.0 S 3.6 Z 6.2
C 1.2 K 2.2 T3.9 3 6.8
D 1.3 L 2.4 V 4.3 4 7.5
E 1.5 N 2.7 W 4.7 7 8.2
H 1.6 O 3.0 X 5.1 9 9.1i, depending on the color capacitor , multiply it by the appropriate factor: Orange - 1
Black - 10
Green - 100
Blue - 1.000
Purple - 10.000
Red - 100.000Naprimer:
H on orange condenser - 1.6 * 1 = 1.6 pF
E on a green capacitor - 1.5 * 100 = 150
9 pF capacitor on blue - 9.1 * 1000 = 9100 pF
If the capacitor is found an inscription, consisting of one uppercase letter and standing next to the figures, find in the table below the corresponding (this letter) numeric value and multiply it by 10 to the extent that is listed after bukvy.A G 10 18 N 33 56 U
B 11 H 20 P 36 V 62
C 12 J 22 Q 39 W 68 D 13 K
24 R 43X 75
E 15 L 27 S 47 Y 82
F 16 M 30 T 51 Z 91Naprimer:
B1 - 11 * (10) = 110 pF
F3 - 16 * (10 * 10 * 10) = 16,000 pF = 16nF= 0.016 uF

Tip 2: How to find the charge

The problems in physics is sometimes necessary to find charge any body based on its interaction with the electric field, or other bodies.In most cases, the dimensions of the body are neglected, not to count the distribution of elementary charge s on its mass or surface.
Finding the value of the elementary charge
For example, how to find charge speck weighing 1 mg which flew in a uniform electric field of 100 kV / m, flew 4 cm and thus its speedIt increased from 1 m / s to 3 m / s?
make a brief record of the task conditions: m = 1 mg, V1 = 1 m / s, V2 = 3 m / s, S = 4cm, E = kV / m, q-?
equate strength informing dust particle acceleration to the force acting on a speck of dust on the part of a uniform electric field.From this equation algebraically express charge mote: it turns out that the product of mass and acceleration of a speck of dust motes equal to the product of the electric field and the charge well;eventually charge dust particles is the ratio of product weight mote and accelerate to the value of the electric field.
Record kinematic equation for determining the acceleration of dust particles: acceleration is defined as the ratio of the difference of squares of the final and initial velocity to twice the value of the path traveled by a particle of dust.
Put this equation in the expression for the charge a speck of dust.The final charge dust particles equals the product of the mass of dust particles and the difference between the squares of the final and initial velocity to twice the product of the distance traveled, and the electric field.
Check dimension of the unknown quantity: it into the final formula to determine charge instead of letters indicating physical quantities, substitute physical units expressed in SI units: unit charge and is defined asThe ratio of product kg • (m / s) to the product of 2 m • V / m;cut in the same unit fraction;Use the definition of physical quantities 1 Newton and Joel 1 and replace certain combinations of physical quantities.
Substituting numerical values, calculate charge motes.Get q = 10 nC
Helpful Hint
Notes: according to Newton's second law tells speck acceleration resultant of all forces acting on a speck of dust;because of the resistance movement of the dust particles is not mentioned, it acts only power - from the electric field.

1 Newton: [1H] = [kg ∙ m / s2];[J] = [N ∙ m];[J / V] = [Cl]

Substituting numerical values ​​set the values ​​of all the physical quantities in the SI;the translation of certain values ​​in order to avoid very bulky or awkward numbers using decimals as a factor of 10 in the number of positive or negative power.