ステップアップノート物理基礎

３１

静電気,啓林館,2019（「基本整理」を英訳して使用）(例)

31. Static Electricity
Static electricity is the electricity that stays still inan object and is produced when an object isrubbed with another object. If one object is charged
positive (+), the other is charged negative (-).
The electric charge on a glass rod rubbed with silk
cloth was defined as positive, and the electric charge
on an ebonite rod rubbed with fur was defined as
negative, and so on.
Electric force is the force between electric charges.
Each electric charge repels the same charge andattracts the opposite.
To possess electricity is called “electrification” or“to be charged”.
The electricity or its quantity on the charged
objects is called electric charge or quantity ofelectricity.
The unit of quantity of electricity is Coulomb (C).
One coulomb is equal to the charge passing per secondby an electric current of one ampere. 1C=1A･1s
Electrons in all materials are light particles withnegative charge. The electric phenomena are causedby the movement of electrons.
Conductors allow electricity to pass through themwell. Metals are generally good conductors. The metalatoms give some electrons (free electrons) and arejoined in metallic bonding.
Insulators such as woods, stones, and rubber
inhibit electricity to flow. All electrons in the atoms
cannot be removed from atoms easily.
Semiconductors, such as Silicon (Si), andGermanium (Ge), have conductivity between that ofconductors and insulators. They are near the border ofmetallic elements and nonmetallic elements in theperiodic table. They are used as electronic parts
because their conductivity changes according tofactors such as temperature and light.

ステップアップノート物理基礎

３２電流,啓林館,2019（「基本整理」を英訳して使用）(例)

32. Electric Current
The electric current intensity is the amount ofcharge that passes through a conductor’s cross section
at any point per second. The current intensity  [A] isdefined asQ
unit: (A)twhere Q [C] is the amount of charge during theItime interval  [s].

Ohm’s law tells us that there is a proportional
relationship between the applied voltage V and theelectric current I .
V  RI
where R , the constant of proportionality, is theelectric resistance. The unit of resistance is ohm (Ω).
The electric resistance  [Ω] is directly
proportional to the length  [m] of the object andinversely proportional to the cross-sectional area [m2].

where  [Ω･m], the constant of proportionality, iscalled the resistivity.
As for resistors in series, all the currents througheach resistor is the same, and the total voltage is thesum of the voltages across each resistor.

V  V1  V2  V3
Total resistance: R  R1  R2  R3
Total voltage:

As for resistors in parallel, all the voltages for eachresistor is the same, and the total current through allresistors is the sum of the currents through eachresistor.
Total current:

I  I1  I 2  I 3

Reciprocal of total resistance:

1
111


R R1 R2 R3

ステップアップノート物理基礎

３３

電力と電力量,啓林館,2019（「基本整理」を英訳して使用）(例)

33. Electric Power and Electric Energy
When the voltage is applied to the resistance wires,
free electrons move and collide with metal atoms. The
thermal motion of atoms becomes more violent andmetal wires generate heat (Joule heat).
The generated heat for t [s] when the applied
voltage is V [V] and the current is  [A] is(Joule’s Law)
Q  VIt

Electric power is the work done by the electriccurrent per second (Power of electric current) orpower consumption by an electric appliance.
When the voltage is V [V], and the current is  [A],the electric power P is

V2
unit: (W)P  VI  RI R(derived using Ohm’s law V  RI )2

Electric energy is the energy supplied by thebattery. The electric energy supplied by the power
P [W] for t [s] isQ  Pt unit: (W･s)=(J)In daily life, we use the unit kilowatt-hour forelectric energy. It is the electric energy consumed
by the power of 1kW per hour, that is (1kWh=3.6×106J) .