Transcript electricity & magnetism

ELECTRICITY &
MAGNETISM
BY: Arana Rampersad
Form: 5D
Physics
ELECTRONICS
RECTIFICATION
RECTIFICATION
What is Rectification?
Rectification is the process of converting
alternating current (a.c.) to direct current
(d.c.). This is done by a device called a
rectifier.


A device which performs the opposite
function (converting DC to AC) is known
as an inverter.
RECTIFICATION

FULL WAVE RECTIFICATION
A full-wave rectifier converts the whole of the input
waveform to one of constant polarity (positive or
negative) at its output. Full-wave rectification
converts both polarities of the input waveform to
DC (direct current), and is more efficient.
RECTIFICATION

HALF WAVE RECTIFICATION
In half wave rectification, either the positive or
negative half of the AC wave is passed, while
the other half is blocked. Because only one half
of the input waveform reaches the output, it is
very inefficient if used for power transfer.
How can a semiconductor diode be
used in half wave rectification


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The two types of semiconductors are: p-type (doped with group
3 elements) and n-type (doped with group 5 elements.)
A diode is used for rectifying an alternating current, i.e., to
obtain from it current which flows in one direction only.
An alternating voltage is applied to the anode by connecting it
to one end of the secondary of a mains transformer, which may
be either step-up or step-down according to the voltage
required. The cathode heater coil is supplied with current from a
separate low-voltage required. The cathode heater coil is
supplied with current from a low-voltage secondary winding on
the same transformer. The unidirectional current output is
obtained from connections made to the other end of the
secondary and the cathode respectively.
How can a semiconductor diode be
used in half wave rectification

The action is that during that half of the cycle when the anode is
positive it attracts electrons from the space charge, and hence
a current flows in the anode circuit. During the other half of the
cycle, when the anode becomes negative, it repels electrons,
and consequently no current flows. The output therefore
consists of a series of impulses or half waves in the same
direction.
Differentiate between direct current
from batteries and rectified alternating
current by a consideration of the V-t
graphs for both cases.
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Rectifying Alternating Current (AC)
Alternating Current (AC) flows one way, then the other
way, continually reversing direction. An AC voltage is
continually changing between positive (+) and
negative (-).
The rate of changing direction is called the frequency
of the AC and it is measured in hertz (Hz) which is the
number of forwards-backwards cycles per second.
Differentiate between direct current
from batteries and rectified alternating
current by a consideration of the V-t
graphs for both cases.
Rectifying Alternating Current (AC)
The diagram below shows a.c. from power supply.
The shape is called a sine wave.

Differentiate between direct current
from batteries and rectified alternating
current by a consideration of the V-t
graphs for both cases.

Direct Current (DC) from batteries.

Direct Current always flows in the same direction, but it may
increase and decrease. A DC voltage is always positive (or
always negative), but it may increase and decrease.
Electronic circuits normally require a steady DC supply
which is constant at one value or a smooth DC supply
which has a small variation called ripple.
Cells, batteries and regulated power supplies provide
steady DC which is ideal for electronic circuits.

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Differentiate between direct current
from batteries and rectified alternating
current by a consideration of the V-t
graphs for both cases.
Direct Current (DC) from batteries.
The diagram below show steady d.c. from a battery.

A simple test to determine whether
a semiconductor diode is defective.

A diode is like a one-way electronic valve. Electrons
flow only one way through a diode junction. When a
source of more positive potential is applied to the
anode, the diode will conduct. This is what is called
"forward biasing". If the diode is reversed, current will
not pass through the diode. This is what is called
"reverse biasing". The circuit shown below shows the
tester light illuminate.
A simple test to determine whether
a semiconductor diode is defective.

The picture shows the tester
illuminating with a diode
forward biased. The cathode
(banded end) of the diode is in
the alligator clip. If you
shorten the alligator clip to the
probe tip you will see a
brighter illumination than
when connected to the diode.
This is called a voltage drop
across the diode junction. If
you reverse the diode, the
tester will not light. This is a
good diode.

If the light illuminates brightly
both ways, or neither way,
the diode is defective. Note
that it must light only in one
direction. If the light
illuminates very dimly on only
one direction and not the
other, the diode may still be
okay.
ELECTRONICS
LOGIC GATES
LOGIC GATES
Logic gates are the fundamental
components in digital electronics.
 There are five basic logic gates: NOT,
AND, OR, NAND and NOR.
 A useful tool which analyses the inputs
and outputs of one or more gates by
logging them in an orderly manner is
known as a truth table.

Symbols for NOT, AND, OR, NAND
and NOR logic gates.

NOT GATE OR INVERTER
A is the input and B is the output.
Symbols for NOT, AND, OR, NAND
and NOR logic gates.
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AND GATE
A and B are the inputs and C is the Output.
Symbols for NOT, AND, OR, NAND
and NOR logic gates.

OR GATE
A and B are the inputs and C is the Output.
Symbols for NOT, AND, OR, NAND
and NOR logic gates.

NAND GATE
A and B are the inputs and C is the Output.
Symbols for NOT, AND, OR, NAND
and NOR logic gates.
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NOR GATE
A and B are the inputs and C is the Output.
The Functions of each gate with
the aid of truth tables.

NOT GATE OR INVERTER
This gate has one input and
one output. The output of a
not gate is the inverse of the
input. For example, if the
input is high or 1 the output
is low or 0.

Truth Table
INPUT
OUTPUT
0
1
1
0
The Functions of each gate with
the aid of truth tables.

AND GATE
This gate has two or more
inputs and one output. The
output is high or on only if all
the inputs are high or on.
Under any other conditions
the output is low or off.

Truth Table
INPUT A
INPUT B
OUTPUT
0
0
0
0
1
0
1
0
0
1
1
1
The Functions of each gate with
the aid of truth tables.

OR GATE
This gate has two or more
inputs and one output. The
output is high or on as long
as one or more of the inputs
are high or on. Under any
other conditions the output is
low or off.

Truth Table
INPUT A
INPUT B
OUTPUT
0
0
0
0
1
1
1
0
1
1
1
1
The Functions of each gate with
the aid of truth tables.

NAND GATE
This gate has two or more
inputs and one output. The
output is low or off only if all
the inputs are high or on.
Under any other conditions
the output is high or on.

Truth Table
INPUT A
INPUT B
OUTPUT
0
0
1
0
1
1
1
0
1
1
1
0
The Functions of each gate with
the aid of truth tables.

NOR GATE
This gate has two or more
inputs and one output. The
output is high or on only if all
the inputs are low or off.
Under any other conditions
the output is low or off.

Truth Table
INPUT A
INPUT B
OUTPUT
0
0
1
0
1
0
1
0
0
1
1
0
Circuits involving the combinations
of no more than three logic gates.
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Constructing a NOT gate
using NAND gates.
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Constructing a OR gate
using NAND gates.
Circuits involving the combinations
of no more than three logic gates.
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Constructing a AND gate
using NAND gates.
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Constructing a NOT gate
using NOR gates.
Circuits involving the combinations
of no more than three logic gates.

Constructing a OR gate
using NOR gates.
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Constructing a AND gate
using NOR gates.