Electrical V11 Home Study

By Clive W. Humphris

An enhanced eBook published in full colour. With EXTENSIVE FREE page and STEM online INTERACTIVE CONTENT enabled with your eBook receipt, explored by inserting any values that could occur in a real situation into hundreds of menu driven topics thereby bringing the topic or any other textbook examples to life.

Full colour graphics that are redrawn for every input change will make your learning experience more enjoyable and effective as it encourages experimentation of real world situations where almost any practical value is accepted.

Interactive Technology when used in the classroom can motivate passive students by encouraging their active participation where STEM subjects are ideally suited to mobile interactive technology on their digital devices.

Students who struggle to be fully engaged in normal classroom activity can often achieve the unexpected once sat in front of a digital screen where they can learn without the embarrassment of full class exposure.

For each topic group students can TEST THEIR UNDERSTANDING by considering an open question whereby their ease of answering will provide an indication of personal progress.

• Language: English
• Publisher: Clive W. Humphris
• Release date: Nov 13, 2012
• ISBN: 9781301503872

Clive W. Humphris

Clive W. Humphris M0DXJ: Ex Technology Teacher. Software Developer, Author and Director of eptsoft limited. Married with two children and four grandchildren.Apprentice Instrument Maker at Marconi’s with Senor Technical Management roles in Radio Rentals and Alcatel Business Systems before starting eptsoft providing educational software to schools colleges and universities worldwide since 1992.Interests outside of developing digital products for eptsoft, include Running, Walking and Reading.

Book preview

SIMPLE DC CIRCUITS: Three Resistors in Series.

Interactive Content!

In a practical circuit consisting of just three resistors, connected in series across a battery, four circuit parameters can be measured using a simple multi-meter. Firstly the current I flowing which is determined by inserting an ammeter in series with the resistors and then the three voltage drops across the individual resistors.

The current is a result of the applied voltage divided by the total series circuit resistance. Apply the formula for series resistance to determine the total resistance R.

Individual resistor voltage drops are each found by applying Ohm's Law. Resistance R1, R2 or R3 multiplied by the series circuit current. Adding the individual voltage drops together will always equal the applied battery voltage.

SIMPLE DC CIRCUITS: Two Parallel Resistors.

Shown are three components connected together forming a circuit. A battery or source of electric current and two resistors. From this diagram a number of circuit parameters may be found. Some are known others need to be calculated.

Considering the current as being 'conventional' where it flows from the battery positive terminal and divides into two branches. The amount of current in each branch will be inversely proportional to the resistor value, i.e. the larger resistor value the less current flows.

Firstly we need to find the total current I, but before we can do this we require the equivalent circuit resistance from the formula. We know the applied battery voltage. However each individual branch current could just as easily be calculated by applying Ohm's Law and the two current values added together which will equal I. Current is never lost (Kirchhoff's Law) the sum of individual currents will always equal the total current.

As you can see there are several ways of solving this problem. If you were given the total current and the resistor values, could you have found the battery voltage?

SIMPLE DC CIRCUITS: Potential Divider.

A simple potential divider is just two resistors connected in series across a battery. So long as we don't have large variations in load current the voltage at the resistor junction will be remain fixed.

The voltage dropped across the lower resistor provides the output voltage, determined by the relationship between Ra and Rb. The calculations will demonstrate this in more detail. What is the output voltage if the lower resistor is made a quarter of the resistance of the upper value?

The simple voltage divider circuit is commonly used to make a transistor base biasing network where the base current requirements are small.

However, there are further considerations when the current requirements increase or are subject to large variations.

SIMPLE DC CIRCUITS: Loading a Potential Divider.

Loading the voltage divider connects the resistance of the load in parallel with the lower resistance Rb. We will call this parallel combination Rx. Note the shorthand for resistors in parallel. To determine the total current, first calculate the value of Rx, then divide the battery or supply voltage by the addition of Ra + Rx.

Load current Iout is simply the resistor junction voltage over the load resistance RL.

In practice the value of Rb is chosen to be about one tenth of the value of the load. This ensures that any fluctuations in load current have a limited effect on the divided output voltage.

Experiment with the values of Rb relative to RL and note the changes on the Ra, Rb junction voltage.

SIMPLE DC CIRCUITS: Pull Up, Down Resistors.

The use of pull up and pull down resistors is a common feature in electronics. Closing S1 in the left hand diagram pulls down the voltage at the lower end of Ra by shorting it to the zero line. Current flowing in Ra will then depend solely upon the resistor value and the supply voltage.

In the diagram to the right, the voltage at the top of Rb is pulled up to the supply voltage by closing S2. With equal value resistors will the current flowing be the same in both circuits when the switches are closed?

S1 and S2 could be replaced by transistors acting as switches which effectively become short circuited between the collector and emitter terminals when made to conduct heavily. Resistor Ra is a collector load and Rb an emitter resistor.

When a transistor is biased OFF, i.e. no base volts the transistor is open circuit. For T1 the collector voltage would be high, no collector current flowing and for T2 the emitter voltage would be zero, with no emitter current flowing. Biasing ON T1 and its collector output voltage is pulled down and for T2 the emitter voltage is pulled up.

TYPES OF SWITCHING: Push Switch.

Interactive Content!

Switch contacts when open provide an interruption of the current flow within a circuit and when closed completes the conducting path. Shown is one of the simplest of schematic diagrams that consists of just three components, indicated by appropriate symbols. Clearly shown are the component connections and the effect of what happens when the switch button is pushed. One of the simplest types of switch has to be the push-to-make, i.e. for a doorbell, here is a push-to-break.

Within the pages of a components catalogue you can find dozens of different combinations of switch types. When selecting a switch there are two main considerations, current rating and the maximum working voltage. Using a switch that is under-rated can be unreliable and dangerous because of arcing of the contacts or physically expose the user to an electric shock because of a voltage breakdown of the insulation.

In this diagram the battery can represent any number of cells connected in series which increase the supply voltage (potential difference) as each cell is added. Battery cells are usually in multiples of 1.5V, and those of the rechargeable type are lower at 1.2V.

To calculate the current I flowing in this simple circuit we can use Ohm's Law by applying the formula shown. Try changing the battery supply voltage and note the changing current. In a practical circuit the more current that flows the brighter the lamp would glow. Increasing the voltage and thereby the current, above that permitted by the bulb and the filament acts like a

Reviews for Electrical V11 Home Study

[Zeeshan Khaliq · Rating: 4 out of 5 stars]

Interactive and covers the complete basics in Electrical & Electronics.
A great resource if you like all the basics at one place with some interactive tools to play with for enhanced understanding.