Transcript i(t)

电气技术专业英语
朱一纶 主编
中国电力出版社
Unit 2 Basic Components
课件制作: 吴岱曦
Index
• Text
– 1.
– 2.
– 3.
– 4.
Resistor
Capacitor
Inductor
Impedance
• Reading materials
– 1. Resistor Color Codes
– 2. Domestic power plugs and sockets
– 3. Battery charger
• Exercises
– 1.
– 2.
– 3.
– 4.
Put the Phrases into English
Put the Phrases into Chinese
Sentence Translation
Translation
Text
1. Resistor
• Suppose that some material is connected
to the terminals of an ideal voltage source
as shown in Fig2.1(a),if the resulting
current i(t) is always directly proportional
to the voltage for any function v(t), then
the material is called a linear resistor, or
resistor for short.
Fig 2.1 the relationship of voltage and current
(a) Connected circuit
(b) i(t) is directly proportional to v(t)
• Since voltage and current are directly
•
proportional for a resistor, there exists a
proportionality constant R, called resistance.
The amount of current flowing in a resistor is
directly proportional to the voltage across it and
inversely proportional to the resistance of the
resistor. This is Ohm law and can be expressed
as a formula: v(t)=Ri(t)
• The units of resistance (volts per ampere)
are referred to as ohms, and are denoted
by the capital Greek letter omega, Ω. A
plot of voltage versus current for a (linear)
resistor is given in Fig 2.1(b).
• Resistors are used to limit current flowing
to a device, thereby preventing it from
burning out, as voltage dividers to reduce
voltage for other device, as transistor
biasing circuits, and to serve as circuit
loads.
• Fig2.2 (a) shows the different resistor
symbols that are used in circuit diagrams.
The rectangular box is used throughout
Europe, while the zig-zag line is more
common in Japan and the USA.
Fig 2.2 Resistors
2. Capacitor
• A capacitor is an electronic device for
temporarily store electrical energy.
Capacitors can be found in almost any
complex electronic circuit. There are many
different types of capacitor but they all
work in essentially the same way.
• A simplified view of a capacitor is a pair of
metal plates separated by a gap in which
there is an insulating material known as
the dielectric. This simplified capacitor is
also chosen as the electronic circuit
symbol for a capacitor is a pair of parallel
plates as shown in Fig2.3(a).
• Some capacitors’ capacitance can be
adjusted, so they are variable capacitors
(Fig 2.3(b)).
Fig 2.3 capacitors
• If voltage is applied to the capacitor
terminals, charge flows in and collects on
one plate. Meanwhile, current flows out of
the other terminal, and a charge of
opposite polarity collects on the other
plate.
• The magnitude of the net charge Q on
one plate is proportional to the applied
voltage V. Thus, we have Q=CV, in which
C is the capacitance.
• A capacitor will block dc current, but
appears to pass ac current by charging
and discharging. It develops an ac
resistance, known as capacitive reactance,
which is affected by the capacitance and
ac frequency. The formula for capacitive
reactance is XC=1/(2πfC C), with units of
ohmsΩ.
3. Inductor
• An inductor is an electrical device, which
can temporarily store electromagnetic
energy in the field about it as long as
current is flowing through it. The inductor
is a coil of wire that may have an air core
or an iron core to increase its inductance.
• The circuit symbols for inductors are
shown in Fig 2.4(a). Some inductors’
inductance can be adjusted; a powered
iron core in the shape of a cylinder may be
adjusted in and out of the core in such
inductors, so they are variable inductors .
Fig 2.4 inductors
• An inductor tends to oppose a change in
electrical current, it has no resistance to
dc current but has an ac resistance to ac
current, known as inductive reactance,
this inductive reactance is affected by
inductance and the ac frequency and is
given by the formula XL=2πfL L, with units
of ohms.
4. Impedance
• Impedance (symbol Z) is a measure of the
overall opposition of a circuit to current, in
other words: how much the circuit
impedes the flow of current. It is like
resistance, but it also takes into account
the effects of capacitance and inductance.
Impedance is measured in ohms, symbol
Ω.
• Impedance is more complex than
resistance because the effects of
capacitance and inductance vary with the
frequency of the current passing through
the circuit and this means impedance
varies with frequency! The effect of
resistance is constant regardless of
frequency.
• The term 'impedance' is often used for
simple circuits which have no capacitance
or inductance - for example to refer to
their 'input impedance' or
'output impedance'. This can seem
confusing if you are learning electronics,
but for these simple circuits you can
assume that it is just another word for
resistance.
• Four electrical quantities determine the
impedance (Z) of a circuit: resistance (R),
capacitance (C), inductance (L) and
frequency (f).
• Impedance can be split into two parts:
Z=R+jX
• Resistance R (the part which is constant
regardless of frequency).
• Reactance X (the part which varies with
frequency due to capacitance and
inductance).
This is the End of the Text
Reading materials
1. Resistor Color Codes
• Components are coded with colors to
identify their value and tolerance，here
takes the resistor as an example.
• The values of the resistor are calculated
from the color of the bands (see Tab 2.1) .
The values of the colors are shown in
Table 2.1. The first band is the tens values.
The second band gives the units; the third
band is a multiplying factor, the factor
being 10’s band value.
• The fourth band gives the tolerance of the
resistor. No band implies a tolerance of ±
20%, a silver band means the resistor has
a tolerance of ± 10% and a gold band
has the closest tolerance of ± 5%.
• For a 5-band resistor, the first band is the
hundreds values. The second band gives
the tens and the third band gives units.
The forth band is a multiplying factor, the
factor being 10’s band value.
• The colors brown, red, green, blue, and
violet are used as tolerance codes on 5band resistors only. All 5-band resistors
use a colored tolerance band.
Table 2.1 The values of the colors
Fig 2.5 Resistor Color Codes
• Fig 2.6 gives some examples of color code
resistor. Resistor in Fig 2.6(a) colored BrownGreen-Grey-Silver-Red would be 1.58 Ω with a
tolerance of ± 2%
• resistor in Fig 2.6(b) colored Yellow-VioletOrange-Gold would be 47 kΩ with a
tolerance of ± 5%.
2. Domestic power plugs and
sockets
• In most countries, household power is
single-phase electric power, in which a
single phase conductor brings alternating
current into a house, and a neutral returns
it to the power supply.
• Domestic power plugs and sockets (Fig
2.7) are devices that connect the home
appliances and portable light fixtures
commonly used in homes to the
commercial power supply so that electric
power can flow to them.
• Many plugs and sockets include a third
contact used for a protective earth ground,
which only carries current in case of a
fault in the connected equipment.
• Power plugs are male electrical connectors
that fit into female electrical sockets. They
have contacts that are pins or blades that
connect mechanically and electrically to
holes or slots in the socket.
• Plugs usually have a phase or hot contact,
a neutral contact, and an optional earth or
Ground contact. Many plugs make no
distinction between the live and neutral
contacts, and in some cases they have
two live contacts. The contacts may be
steel or brass, either zinc, tin or nickel
plated.
• Power sockets are female electrical
connectors that have slots or holes which
accept the pins or blades of power plugs
inserted into them and deliver electricity
to the plugs.
• Sockets are usually designed to reject any
plug which is not built to the same
electrical standard. Some sockets have
one or more holes that connect to pins on
the plug.
Fig 2.7 Domestic power Various
Plugs & Sockets
3. Battery charger
• A battery charger is a device used to put
energy into a secondary cell or
(rechargeable) battery by forcing an
electric current through it.
• The charge current depends upon the
technology and capacity of the battery
being charged. For example, the current
that should be applied to recharge a 12 V
car battery will be very different from the
current for a mobile phone battery.
• A simple charger works by connecting a
constant DC power source to the battery
being charged. The simple charger does
not alter its output based on time or the
charge on the battery. This simplicity
means that a simple charger is
inexpensive, but there is a tradeoff in
quality.
• Typically, a simple charger takes longer to
charge a battery to prevent severe overcharging. Even so, a battery left in a
simple charger for too long will be
weakened or destroyed due to overcharging.
• A trickle charger is a kind of simple
charger that charges the battery slowly, at
the self-discharge rate. A trickle charger is
the slowest kind of battery charger.
Leaving a battery in a trickle charger
keeps the battery "topped up" but never
over-charges.
• The output of a timer charger is
terminated after a pre-determined time.
Timer chargers were the most common
type for high-capacity Ni-Cd cells in the
late 1990s.Often a timer charger and set
of batteries could be bought as a bundle
and the charger time was set to suit those
batteries.
• If batteries of lower capacity were
charged then they would be overcharged,
and if batteries of higher capacity were
charged they would be only partly charged.
• An intelligent charger is that it’s output
current depends upon the battery's state.
An intelligent charger may monitor the
battery's voltage, temperature and/or time
under charge to determine the optimum
charge current at that instant.
• Charging is terminated when a
combination of the voltage, temperature
and/or time indicates that the battery is
fully charged.
This is the End of
the Reading materials
Exercises
• Ready to go?
1. Put the Phrases into English
• 1）一个理想电压源
• 2）比例常数
• 3）欧姆定律
• 4）电子器件
• 5）可变电容
Show the Answer
• 6）阻挡直流
• 7）感抗
• 8）电磁能
• 9）交流电频率
• 10）输入阻抗
Show the Answer
2. Put the Phrases into Chinese
• 1）linear resistor
• 2）be inversely proportional to
• 3）circuit diagram
• 4）simplified capacitor
• 5）pass ac current
Show the Answer
• 6）capacitive reactance
• 7）as long as
• 8）powered iron core
• 9）variable inductors
• 10）take into account
Show the Answer
3. Sentence Translation
• 1）Suppose that some material is
connected to the terminals of an ideal
voltage source.
• 1）假设在某一器件的两端加上一个理想电
压源。
• 2) Resistors are used as voltage dividers
to reduce voltage for other device.
• 2）电阻可用于分压，减小其他器件的电压 。
• 3) There are many different types of
capacitor but they all work in essentially
the same way.
• 3）电容的种类很多，但它们的基本工作原
理都是一样的。
• 4) The magnitude of the net charge Q on
one plate is proportional to the applied
voltage V.
• 4）一块极板上聚集电荷的多少取决于所加
的电压。
• 5) Impedance is more complex than resistance
because the effects of capacitance and
inductance vary with the frequency of the
current passing through the circuit.
• 5）阻抗比电阻复杂，因为电容和电感（对
电流的阻碍）作用是会随着流过电路的电
流的频率变化而变化的。
4．Translation
• Standard-type resistors usually maintain
their value regardless of external
conditions, such as voltage, temperature,
and light. These types of resistors are
referred to as linear resistors.
• There are other types of resistors referred
to as nonlinear, whose resistance varies
with temperature (thermistor 热敏电
阻),voltage(varistor变阻器) and light.
Show the Answer
This is the End of the
Exercises
Good work everyone !!!
(习题答案仅供参考)
That is the End of Lecture
Thank you