electricity and electronic

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Electricity and Electronic Lesson 2, Technology Sección bilingüe Xosé M. Rodríguez

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Electricidade e electrónica en inglés para a sección bilingüe de tecnoloxía de 3º ESO

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Page 1: Electricity and Electronic

Electricity and Electronic

Lesson 2, TechnologySección bilingüe

Xosé M. Rodríguez

Page 2: Electricity and Electronic

Electrical magnitudes

• Voltage (sometimes also called electric potential difference or electrical tension) is the electrical potential difference between two points

of an electrical or electronic circuit, expressed in volts.

• Electric current is the flow of electrical charge. The amount of electric charges flowing through a section in a second. The SI unit of electric current is the ampere.

• Electrical resistance is a measurement of the difficulty encountered by an electric current through an electrical circuit. Resistance is measured in ohms (Ω).

Page 3: Electricity and Electronic

Ohm's law.

The direct current flowing in an electrical circuit is directly proportional to the voltage applied to the circuit. The constant of proportionality R, called the electrical resistance, is given by the equation below,

V I R

Page 4: Electricity and Electronic

Resistors associationResistors in a parallel: In this configuration

each resistor has the same voltage. To find their total equivalent resistance (Req):

1R eq

1R1

1R2

...1Rn

Page 5: Electricity and Electronic

Resistors association

Resistor in Series: the current through resistors in series stays the same, but the voltage across each resistor can be different. The sum of the potential differences (voltage) is equal to the total voltage. To find their total resistance:

R eq R1 R2 ... Rn

Page 6: Electricity and Electronic

Electronic devices

http://www.bbc.co.uk/schools/gcsebitesize/design/electronics/materialscomponentsrev1.shtml

Page 7: Electricity and Electronic

Resistors

A resistor is a two-terminal electronic component designed to oppose an electric current by producing a voltage drop between its terminals in proportion to the current.

Color code of resistors

Page 8: Electricity and Electronic

Variable resistorsA potentiometer is a three-terminal resistor with a sliding contact to change the value.

Potenciometer.

LDR (Light Dependent Resistor)

Is a resistor whose resistance decreases with increasing incident light intensity

Temperature Dependent Resistors

NTC

PTC Is a resistor whose resistance increases with increasing temperature.

Is a resistor whose resistance decreases with increasing temperature.

Page 9: Electricity and Electronic

Semiconductors

A diode is the simplest form of semiconductor. Diodes are a discrete component that allows current to flow in one direction only.

The direction that current is allowed to pass is called the forward bias. The direction that current is not allowed to pass is called the reverse bias. A diode has two leads: for forward bias, the current comes in at the anode (positive lead) and out at the cathode (negative lead).

Forward Reverse

Page 10: Electricity and Electronic

LED

A LED is a semiconductor diode that emits light when an electric current is applied in the forward direction of the device.

Page 11: Electricity and Electronic

TransistorElectronics began with the development of the transistor in the 1950s. Transistors are essentially tiny semiconductor amplifiers and/or switches, several thousands of which can be put on a 1mm2 piece of silicon.

Transistors have three leads:

emitter,

collector

base.

The base lead controls the transistor: applying an electrical current to the base lead switches the transistor on. When the transistor is on, current flows from the collector to the emitter - but when it is off no current will flow.

NPN

PNP

Page 12: Electricity and Electronic

Transistors are easily damaged, so it is important not to mix up the three leads. To help identify the leads some transistors have a dot near the collector, and/or a tab near the emitter. Each type of transistor is identified by a code

printed on the side and then you can learn about it in the datasheet.

Page 13: Electricity and Electronic

Transistors: regions of operation

• Active. Ic = GAIN . IB

• Saturation: the base electrical current (IB) is high, then the collector electrical current (IC) is constant, Isat, called saturation current.

• Cutoff: the base electrical current is zero, IB=0 A, or very low, then there is no current in the collector, IC=0 A. The transistor doesn´t allow the flow of charges.

Page 14: Electricity and Electronic

Some transistors

Page 15: Electricity and Electronic

Darlington pairsSome transistors can take a very low current flowing in the base and amplify it to give a much higher

current in the collector (called gain). Other transistors can output a large current at the collector - but without very much gain. Single transistors cannot have both high gain and high collector current.

To overcome this problem, a high-gain transistor is paired up with a high-current

transistor in what is called a Darlington pair. The combined transistors allows both a higher gain and a larger amount of current to flow than would be possible with a single transistor. Darlington pairs are often used to drive motors.

Page 16: Electricity and Electronic

Transistor

• http://www.ieee-virtual-museum.org/media/Transistor_final.swf

Page 17: Electricity and Electronic

CapacitorA capacitor is a discrete component which can store an electrical charge for a period of time. The larger the capacitance the more charge it can store.The unit of measurement of a capacitor is the farad. Often you will see capacitors of much less than a farad. These will be measured in microfarads (one millionth of a farad or 1/1,000,000) or picofarads (one million-millionth of a farad or 1/1,000,000,000,000).There are two types of capacitor:•polarised or electrolytic capacitors, and•non-polarised or non-electrolytic capacitors

Page 18: Electricity and Electronic

Some capacitors

Page 19: Electricity and Electronic

Relay• Relay: is an electrical switch that opens and closes under the

control of another electrical circuit. The switch is operated by an electromagnet to open or close one or many sets of contacts.

Page 20: Electricity and Electronic
Page 21: Electricity and Electronic
Page 22: Electricity and Electronic

Very simple circuit Light sensor

Page 23: Electricity and Electronic

Vs VinR1

R1 Rldr

Vin

Potential divider

Page 24: Electricity and Electronic

IBase

Cutoff:

IBASE = 0 A => ICollector = 0 A

Saturation:

IBASE is high => ICollector = ICSAT

Icollector

BC548 ICSAT = 10 mA Look for this data in the web (datasheet)

Iemitter

Page 25: Electricity and Electronic
Page 26: Electricity and Electronic

Humidity sensor