Reference:Nelson PhysicsVCE Units 3 & 4Chapters 9 and 10Page 219
ES.1Charge
The unit of charge is the coulomb (C)
1 coulomb = 6.25 ´ 1018 electronic charges (the charge on an electron)
The charge on 1 electron1.60 ´ 10-19C.
ES.2Electric
Current
Electric current is the movement of charges. It is the measure of the amount of charge passing a point every second.
whereQ = Charge in coulomb
t = time interval in seconds
The units of current are Ampere (Amp).
The direction of current is the direction of movement of the positive charges. ie. positive to negative. We know that it is really the electrons that move, but this definition stays for historical reasons.
ES.3Voltage
When a charge passes through a battery it is given energy When it passes around a circuit it loses this energy to the circuit elements (perhaps a light globe).
The term voltage is used to refer to the amount of energy that is given to a charge or is used up by a charge when moving around a circuit.
The voltage of a battery refers to how many joules are given to each coulomb of charge:
1 V = 1 JC-1
Voltage is some times referred to as potential difference, the difference in potential energy of a charge at two different places in a circuit.
ES.4Power
The rate at which energy is supplied by a battery, or is used up in a circuit element, is called power
The energy supplied by a battery
is voltage(V) ´
amount of charge(Q). The time can be related to the current by 
Watt
(W)
ES.5Voltage
and Current in a Circuit
I2 + I3 = I1In parallel the currents add up
V1 = V2In parallel potential differences are the same.
V1 + V3 = EMF In series potential differences add up
ES.6Ohm's
Law
In any Circuit, if a circuit element gives a straight line graph of I Vs V, as shown
It is said that the element obeys Ohm's Law
VµI
R is called the resistance and is measured in Ohms (W)
ES.7Alternative
Expressions for Power
We knowP = V I
but Ohm's law says V = I R
So we can get two alternate expressions for power
Example:
A light globe is rated as 75 W, it has a current of 500 mA flowing through it. What is the resistance of the light globe?
Problem Set #1: Gardiner & McKittrick Page 167 Questions 7 - 11 (Worksheet)
ES.8Resistances
A resistor or a resistance is a circuit element that resists the flow of electricity (electrons). The higher the number the higher the resistance. The units of resistance are Ohms (W).
ES.8.1Resistors
in Series
In a series circuit, the current leaves the battery, travels around the loop of the circuit passing through each circuit element. As the charges move through each circuit element they loose potential (energy) until they arrive back at the battery terminal with no energy left. In a series circuit the current is the same throughout the circuit.
We can say that the sum of the energies lost in the circuit = the energy supplied by the battery.
i.e.E = V1 + V2 + V3 + ……
from Ohm's law V = I R
we getI RT =I R1 + I R2 + I R3 + ……
since I is the same around the circuit
I RT = I (R1 + R2 + R3 + ……)
So
Example: Find the total resistance in the circuit below
ES.8.2Resistors in Parallel
In a parallel circuit the current splits up into two or more components while the voltage across each element in the parallel connection is constant.
ThusIT = I1 + I2 + I3 + ……
FromV = I R
substituting we get
Since V is the same for all resistances
Example:Find the total resistance in the following circuit
Problem Set #2:Gardiner & McKittrick Page 170Questions 32, 36 - 41 (Worksheet)
ES.9Non-Ohmic
Devices
Many components used in circuits have voltage/current relationships which are quite different to those of Ohm's law. i.e. a graph of V vs I does not give a straight line.
Solid State Diode
Neon Lamp
Light Dependant Resistor
Problem Set #3:Gardiner & McKittrick Page 160 Questions 19 -24 (Worksheet)
ES.10Alternating
Current
Alternating current is where the direction of flow of the current continually changes. The number of times the direction changes every second is called frequency. The frequency is governed by the speed of rotation of the generator.In Australia the standard frequency is 50 Hz.
A graph of our domestic power supply, 240 V, 50 Hz AC; varies as follows:
Note:The peak voltage is340 volts, but the electricity is given the value that corresponds to the power transfer of a.240 V DC battery.This is also known as the root mean square (RMS) value and is calculated as follows:
and
Problem Set #4:Gardiner & McKittrick Page 191 Questions 1 - 5 (Worksheet)
TextPage 239Questions 1, 2, 3
ES.11Power
Supplies
There are two types of power supply AC and DC.AC power supplies are generators (we have done these to death). Many of the things we use in our homes used AC power. However Electronic equipment uses DC power.There are two ways that DC power can be supplied
i) from a battery
ii) by changing the AC power
When AC power is changed to DC it is said to be rectified.
Rectifiers are made with diodes and capacitors. A diode allows current to flow in only one direction and capacitors store charge for a short while.
ES.11.1Half-wave
Rectifier
This type of rectifier is very simple and involves only one diode. It allows the current to flow one way. The effect on the AC current is that we end up with half a wave.
ES.11.2Full-wave
Rectifier
This type of rectifier involves four diodes. The effect is to flip over the bottom part of the current. It is also known as a bridge rectifier.
The output of these rectifiers flows in one direction but still varies. To stop this variation a capacitor is used, this stores some charge and releases it when the voltage drops off. The effect is to smooth out the out put. The larger the value of the capacitor (C) the greater the smoothing effect.
Capacitance is defined as the ratio of the charge on the plate to the potential difference between the plates. The unit is farad (F).
The time it takes for a capacitor to charge up is called capacitive time constant.For a series resistive-capacitive (RC) circuit it is given by
After one time constant the capacitor is 63% charged or discharged.The capacitor charges or discharges exponentially.
Note:A capacitor is considered fully charged (or discharged) after five time constants.
Example
Find the time constant for a series circuit containing a 1.0 MW resistor and a 2.0 mF capacitor
t = R C
= 1.0 ´106´ 2.0 ´ 10-6
= 2.0 s
Problem Set #5:Gardiner & McKittrick Page 196 Questions 34 - 37
Gardiner & McKittrick Page 194 Questions 15 - 21 (Worksheet)
TextPage 240Questions 8, 11 – 18, not 14
TextPage 264Questions 1, 2, 4
ES.12Voltage
Dividers
Sometimes the voltage supplied is greater than that needed by the circuit. For AC power a transformer is used, but DC power requires a voltage divider to be used.
A voltage divider consists of a series of resistors.
Since the resistance of the circuit is R1 + R2,
we can write Vin = I (R1 + R2)
The output voltage will be equal to the voltage across the second resistor
i.e.Vout
= I R2
thus we have
If we have a load resistor attached to the output then the situation changes slightly.
We must first calculate the effective resistance of the parallel resistors. The equation stays the same but R2 is replaced with the effective resistance.
Examples.
1.A voltage divider is set up using a 1.0 KW resistor and a 2.0 KW resistor in series. If the input voltage is 6.0 V what is the output across the 2.0 KW resistor
Vout=4.0 V
2.Now a load resistor of 2.0 KW is connected in parallel with the output resistor Calculate the new output voltage.
Reff=1.0 ´
103
Hence
Vout = 3.0 V
The ratio 
is
also known as voltage gain.
ES.13Voltage
Amplifiers
Do example of graph on board.
No clipping or non linear.
When a DC voltage needs to be increased a voltage amplifier needs to be used. This device takes the input voltage and provides a larger output voltage. A voltage amplifier is also connected to an external power supply, it takes some power from this external power supply.
Voltage amplifiers are a complex arrangement of transistors and resistors. They are available as integrated circuits (IC's) and are called operational amplifiers.
The properties of a voltage amplifier can be summarised as follows:
·inputs are the small AC signal with peak to peak voltageDVIN to be amplified and a power source
·output is a larger AC signal of peak to peak voltage DVOUT
·the amplification of the input voltage is called the gain and should be the same for all inputs
·the simplest amplifier has a single transistor but this inverts the AC signal
·the inverting amplifier acts as NOT logic gate - that is, the output is high when the input is low and the output is low when the input is high
·most amplifiers distort the output signal by clipping if DVINis too large
ES.14Input
/ Output Transducers
In electrical circuits the input is often not electrical. Inputs can be anything from turning on a switch to a CD player.
Input devices are called transducers and convert the input into electrical energy which is then processed by the next stage of the circuit.
Output devices are also called transducers, these convert electrical energy to other forms, such as heat, light, sound and mechanical. A common output transducer is a loud speaker
Some typical input transducers are:
Microphone, Mechanical switches, Heat-dependant resistors or thermisters, Photo-transistors or Light dependant resistors, Pressure transducer, Magnetic field detectors, Moisture detectors, Infra-red detectors, K-rag and radiation detectors.
Some typical output transducers are:
Lights, Loudspeakers and other noise generating devices, Meters, Motors, Magnets, Liquid crystal displays.
More information on these is in your text on pages 247 and 248.
Problem Set #6:Gardiner & McKittrick Page 178 Questions 14 - 16 (Worksheet)
TextPage239Questions 1 – 7, 19 - 29
ES.15Electronic
Logic Gates
Logic gates are electronic devices that operate by being either on or off, true or false. If we use 1 = true and 0 = false then the logic processes can be represented in the form of binary number.Since the process can be represented by a digit it is sometimes called digital.
ES.15.1The
Binary System
There are a number of binary-based systems, these include octal, hexadecimal and alphanumeric. The binary numbers we are most interested in work on the base two system, that uses only the digits 0 and 1. Each binary digit is called a bit. The binary equivalent to the first fifteen decimal numbers is shown below.
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A group of digits is called a word.An 8-bit word is called a byte.
The 0 and 1 values can represent a number of different things, off or on, low or high, voltage levels 0 V or +5 V, and finally false or true.
ES.15.2Logic
Gates
Prac #3.11:Logic
Gates
Digital electronics involves the study and conveying of information. In this process decisions are made and voltages switched from one to the other i.e. 1 to 0 or vise versa. The devices that make these decisions are called logic gates. There are seven main types of logic gate, each of these makes a different type of decision.
ES.
15.2.1AND Gate
The AND gate compares inputs and then gives an output. If both inputs are High i.e. 1 then the output is High, otherwise the output is low.For a two input AND gate this means A and B must be High for the output to be High. The symbol for an AND gate is shown below.
The Inputs and outputs of logic gates can be summarised in a table called a Truth Table. The truth table for the AND gate is shown below.
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The condition that both A and B must be high for Q to be high is written as:
Q = A AND B = A·B
ES.
15.2.2 OR Gate
The OR gate compares inputs and then gives an output.If one or both of the inputs are High i.e. 1 then the output is High, otherwise the output is low.For a two input or gate this means A OR B OR both must be High for the output to be High.The symbol for an OR gate is shown below.
The truth table for the OR gate is shown below.
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A
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B
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Q
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0
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0
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0
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0
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1
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1
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1
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0
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1
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1
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1
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1
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The condition that both A or B or both must be high for Q to be high is written as:
Q = A OR B = A + B
ES.
15.2.3EXCLUSIVE OR Gate
There is another type of OR gate, that is one where one or other of the inputs is high then the output is high. i.e. only one of the inputs can be high. This is called the EXCLUSIVE OR gate. If one or other of the inputs are High i.e. 1 then the output is High, otherwise the output is low. For a two input or gate this means A OR B only must be High for the output to be High. The symbol for an EXCLUSIVE OR gate is shown below.
The truth table for the EXCLUSIVE OR gate is shown below.
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A
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B
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Q
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0
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0
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0
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0
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1
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1
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1
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0
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1
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1
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1
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0
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The condition that both A or B only must be high for Q to be high is written as:
Q = A XOR B = AÅB
ES.
15.2.4INVERTER or NOT Gate
As the name suggests an INVERTER or NOT gate changes the highs to lows and the lows to highs thus inverting the input signals. The symbol for the NOT gate is shown below:
The truth table for the NOT gate is shown below:
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A
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Q
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1
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0
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0
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1
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Q
= NOT A = 
(A
bar)
ES.
15.2.5NOR Gate
The NOR gate compares inputs and then gives an output.If one or both of the inputs are high then the output is low, otherwise the output is high.For a two input NOR gate this means A OR B OR both must be high for the output to be low.Alternatively the output is High if neither input A NOR input B is 1.The symbol for an NOR gate is shown below.
This gate is a combination of an OR gate followed by a NOT gate. The truth table for the NOR gate is shown below.
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A
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B
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Q
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0
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0
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1
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0
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1
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1
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0
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0
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1
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1
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0
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Q = A NOR B
ES.
15.2.6NAND Gate
The NAND gate compares inputs and then gives an output.If both of the inputs are High, then the output is Low, otherwise the output is High.For a two input NAND gate this means A and B must be High for the output to be low. The symbol for an NAND gate is shown below.
This gate is a combination of an AND gate followed by a NOT gate.
The truth table for the NAND gate is shown below.
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A
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B
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Q
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0
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0
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1
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0
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1
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1
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1
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0
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1
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1
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1
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0
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This is written as:
Q = A NAND B
ES.
15.2.7BUFFER
There is one other type of logic device, it is not really a logic gate since it does not make decisions.It is a buffer.The purpose of a buffer is to boost the input signal without changing the output. The symbol for a buffer is shown below:
The truth table for a buffer is:
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A
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Q
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0
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0
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1
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1
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Prac #3.12:Combining Logic Gates
Problem Set #7: TextPage 264Questions 6 – 20, 22 – 25
ES.15.3Flip
Flops
Prac #3.13:The Flip Flop
Flip Flops can be constructed in various ways.The simplest Flip Flop is a combination of NAND gates or a combination of NOR gates. These gates are connected as shown below.
There are a number of types of Flip Flop, these include RS flip flops, D-type flip flops, JK flip flops and T-type flip flops. The circuit symbols for each of these is shown below.
You will have noticed that the outputs
of the flip flops have the symbols Q and 
.This
is because at all times the values of these is opposite, if Q =1 then 
=
0 and vise versa. Thus when Q changes state then 
will
also change state.For this reason
they are called flip flops.Flip
flops are a one bit memory, storing either logic 1 if Q =1 or logic 0 if
Q = 0.
Let us look more closely at the RS flip flop.When the S input receives a high then Q goes high, this will then be stored until R goes high.However if the S input is high when R is high then no change occurs. This is summarised in the table below.
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The operation of a D-type flip flop is very simple.The Q output follows the D input but will only change when the CK goes from low to high.In other words Q takes the value of D when CK goes high.If CK remains high, goes low or remains low then the value of Q remains unchanged no matter what D does. The graphs below indicate this.
The JK flip flop operates in a similar fashion to the RS flip flop.When the two inputs are not equal the Q follows J.When the inputs are both 0 the output does not change.When the inputs are both 1 the Q toggles (i.e. changes from 0 to 1 or 1 to 0). This is summarised In the table below.
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Problem Set #8:TextPage 266Questions21, 26, 27
ES.15.4Registers
A register is a device that stores information, they are usually constructed by combining a number of flip flops. There are two types of register, parallel and series. Parallel registers are quicker but they also require more circuitry.
Registers work by storing the data input signal when a pulse received from the clock. The construction of a parallel register is shown below:
ES.1 5.5Counters
Counter are a series of flip flops where the output of one is fed directly into the input of the next.To construct a counter a special type of T-type flip flop is used, it is one where the out put changes when the input changes from high to low (a falling edge flip flop).A common construction is shown below:
Each input pulse P causes A to change state.Every time A changes from high to low, it causes B to change state and every time B changes from high to low, it causes C to change state.The truth table for this counter is shown below:
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Note:On the eighth pulse the counter resets.
ES.
15.6Oscillators
An oscillator is a device that produces
a signal that alternates between two values.An
oscillator is constructed by connecting the output signal to the input,
with some delay in between.This
is called feedback.Oscillators are
used to provide an audio signal in an alarm circuit, the clock pulses to
control a computer or any other regularly changing signal.
Problem Set #9:TextPage 268Questions 28 – 31
Prac #3.14:Operational
Systems