***Useful Information for Apprentices***

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“ General Health and Safety at Work “

Question 1.1
What do the letters CDM stand for ?
A: Control of Demolition and Management Regulations
B: Control of Dangerous Materials Regulations
C: Construction (Demolition Management) Regulations
D: Construction (Design and Management Regulations ) Answer: D )
Question 1.2
Identify one method of enforcing regulations that are
available to the Health and Safety Executive:
A: Health Notice
B: Improvement Notice
C: Obstruction Notice
D: Increasing insurance premiums
Answer: B Improvement notices require action to achieve standards which meet health and safety law :
Question 1.3
What happens if a Prohibition Notice is issued by an
Inspector of the local authority or the HSE ?
A: The work in hand can be completed, but no new work started
B: The work can continue if adequate safety precautions are put in place
C: The work that is subject to the notice must cease
D: The work can continue, provided a risk assessment is carried out,
Answer: C The work covered by a prohibition notice must cease until the identified danger is removed.
Question 1.4
Health and Safety Executive Inspector can ?
A: Only visit if they have made an appointment
B: Visit at any time
C: Only visit if accompanied by the principal contractor
D: Only visit to interview the site manager
Answer: B Inspectors have a range of powers, including the right to visit premises at any time.
Question 1.5
A Prohibition Notice means:
A: When you finish the work you must not start again
B: The work must stop immediately
C: Work is to stop for that day only
D: Work may continue until the end of the day
Answer: B The work activity covered by the prohibition notice must cease, until the identified danger is removed ,
Question 1.6
In what circumstances can an HSE Improvement Notice be issued ?
A: If there is a breach of legal requirements
B: By warrant through the police
C: Only between Monday and Friday on site
Answer: A Improvement notices require action to achieve standards which meet health and safety law .
Question 1.7
What is an “Improvement Notice”?
A: A notice issued by the site principal contractor to tidy up the site
B: A notice from the client to the principal contractor to speed up the work
C: A notice issued by a Building Control Officer to deepen foundations
D: A notice issued by an HSE/local authority Inspector to enforce compliance with health
Answer: D Improvement notices require action to achieve standards which meet health and safety law .
Question 1.8
If a Health and Safety Executive Inspector issues a“ Prohibition Notice”, this means that:
A: the Site Manager can choose whether or not to ignore the notice
B: specific work activities, highlighted on the notice, must stop
C: the HSE must supervise the work covered by the notice
D: the HSE must supervise all work from then on
Answer: B Prohibition notices are intended to Stop activities which can cause serious injury.
Question 1.9
Which one of the following items of information will you find on the Approved Health and Safety Law poster?
A: Details of emergency escape routes
B: The location of the local HSE office
C: The location of all fire extinguishers
D: The identity of the first aiders
Answer: B The poster also lists the persons with health and safety responsibilities, but not first aiders.
Question 1.10
Who is responsible for signing a Company Safety Policy ?
A: Site Manager
B: Company Safety Officer
C: Company Secretary
D: Managing Director
Answer: D The Health and Safety at Work Act requires the most senior member of management to sign the health and safety policy
statement.

Question 1.11
Which one of the following must be in a company’s written Health and Safety Policy:
A: Aims and objectives of the company
B: Organisation and arrangements in force for carrying out the health and safety policy
C: Name of the Health and Safety Adviser
D: Company Director’s home address
Answer: B This requirement appears in the Health and Safety at Work Act.
Question 1.12
Employers have to produce a written Health and Safety Policy statement when:
A: A contract commences
B: They employ five people or more
C: The safety representative requests it
D: The HSE notifies them
Answer: B This is a specific requirement of the Health and Safety at Work Act.
Question 1.13
Companies employing five or more people must have a written Health and Safety Policy because:
A: The principal contractor gives them work on site
B: The HSAWA 1974 requires it
C: The Social Security Act requires it
D: The trade unions require it
Answer: B
Question 1.14
What do the letters HSC stand for ?
A: Health and Safety Contract
B: Health and Safety Consultant
C: Health and Safety Conditions
D: Health and Safety Commission Answer: D
Question 1.15
Which ONE of the following statements is correct ? The Health and Safety Executive is:
A: a prosecuting authority
B: an enforcing authority
C: a statutory provisions authority
Answer: B The Health and Safety Executive enforces health and safety legislation.
Question 1.16
The Health and Safety at Work Act requires employers to provide what for their employees?
A: Adequate rest periods
B: Payment for work done
C: A safe place of work
D: Suitable transport to work
Answer: C This is a specific requirement of Section 2 of the Health and Safety at Work Act.
Question 1.17
The Health and Safety at Work Act 1974 and any regulations made under the Act are:
A: Not compulsory, but should be complied with if convenient
B: Advisory to companies and individuals
C: Practical advice for the employer to follow
D: Legally binding Answer: D
Question 1.18
Under the Health and Safety at Work Act 1974, which of the following have a duty to work safely?
A: Employees only
B: The general public
C: Employers only
D: All people at work
Answer: D Employers, employees and the self-employed all have a duty to work safely under the Act.
Question 1.19
What is the MAXIMUM penalty that a Higher Court, can currently impose for a breach of the Health and Safety at Work Act?
A: £20,000 fine and two years imprisonment
B: £15,000 fine and three years imprisonment
C: £1,000 fine and six months imprisonment
D: Unlimited fine and two years imprisonment
Answer: D A Lower Court can impose a fine of up to £20,000 and/or up to six months imprisonment for certain offences. The potential fine in a Higher Court, however, is unlimited and the term of imprisonment can be up to 2 years.
Question 1.20
What do the letters ACoP stand for ?
A: Accepted Code of Provisions
B: Approved Condition of Practice
C: Approved Code of Practice
D: Accepted Code of Practice
Answer: C An ACOP is a code of practice approved by the Health and Safety Commission.

Question 1.21
Where should you look for Official advice on health and safety matters?
A: A set of health and safety guidelines provided by suppliers
B: The health and safety rules as laid down by the employer
C: Guidance issued by the Health and Safety Executive
D: A professionally approved guide book on regulations
Answer: C The HSE is the UK enforcing body and its guidance can be regarded as ‘official’
Question 1.22
Regulations that govern health and safety on construction sites:
A: apply only to inexperienced workers
B: do not apply during ’out of hours’ working
C: apply only to large companies
D: are mandatory ( that is, compulsory )
Answer: D The requirements of health and safety law are mandatory, and failure to follow them can lead to prosecutions.
Question 1.23
Which of the following statements is correct ?
A: The duty for health and safety falls only on the employer
B: All employees must take reasonable care, not only to protect themselves but also their colleagues
C: Employees have no responsibility for Health and Safety on site
D: Only the client is responsible for safety on site
Answer: B The responsibility for management of Health and Safety Act at Work rests with the employer
Question 1.25
Which of the following is correct for risk assessment?
A: It is a good idea but not essential
B: Only required to be done for hazardous work
C: Must always be done
D: Only required on major jobs
Answer: C There is a legal requirement for all work to be suitably risk assessed.
Question 1.26
In the context of a risk assessment, what do you understand by the term risk?
A: An unsafe act or condition
B: Something with the potential to cause injury
C: Any work activity that can be described as dangerous
D: The likelihood that harm from a particular hazard will occur
Answer: D Hazard and risk are not the same. Risk reflects the chance of being harmed by a hazard
Question 1.27
Who would you expect to carry out a risk assessment on your working site?
A: The site planning supervisor
B: A visiting HSE Inspector
C: The construction project designer
D: A competent person
Answer: D A risk assessment must be conducted by a 'competent person’.
Question 1.28
What is a HAZARD ?
A: Where an accident is likely to happen
B: An accident waiting to happen
C: Something with the potential to cause harm
D: The likelihood of something going wrong
Answer: C Examples of hazards include: a drum of acid, breeze blocks on an elevated plank; cables running across a floor.
Question 1.29
What must be done before any work begins ?
A: Emergency plan
B: Assessment of risk
C: Soil assessment
D: Geological survey
Answer: B This is a legal requirement of the Management of Health and Safety at Work Regulations.
Question 1.30
Complete the following sentence: A risk assessment
A: is a piece of paper required by law
B: prevents accidents
C: is a means of analysing what might go wrong
D: isn’t particularly useful
Answer: C Risk assessment involves a careful review of what can cause harm and the practical measures to be taken to reduce the risk of harm.

 

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50) a heavy electric motor is very likely to be fixed to a concrete floor by :
a) wood screws and plastic plugs ,
b) a clip on girder fixing ,
c) an expansion bolt , ◄
d) a spring toggle bolt ,
51) A run of trunking suspended in an industrial installation is very likely to be fixed to the main structure of the building by :
a) wood screws and plastic plugs ,
b) a clip on girder fixing , ◄
c) an expansion bolt ,
d) a spring toggle bolt ,
52) A run of cable tray suspended in a modern Supermarket building is very likely to be attached to the main structure of the :
a) wood screws and plastic plugs ,
b) a clip on girder fixing , ◄
c) an expansion bolt ,
d) a spring toggle bolt ,
53) what action is necessary to produce a “ secure electrical isolation “ :
a) isolate the supply and observe that the voltage indicator reads zero ,
b) First connect a test device such as a voltage indicator to the supply ,
c) Larger pieces of equipment may require isolating at a local isolator switch ,
d) The isolated supply must be locked off or secured with a small padlock , ◄
54) A voltage proving unit :
a) is used for transmitting data along optical fibre cables ,
b) provides a secure computer supply ,
c) shows a voltage indicator to be working correctly , ◄
d) tests for the presence of a mains voltage supply ,
55) for working even a short distance above ground level periods , the safest piece of access equipment would be :
a) a stepladder ,
b) a platform tower , ◄
c) an extension ladder ,
d) a hard hat ,
56) an example of “ special waste : is :
a) sheets of asbestos , ◄
b) old fibre-glass roof insulation ,
c) old fluorescent tubes , ◄
d) part coils of PVC insulated cables ,
57) Special Waste must be disposed of :
a) in the general site skips ,
b) in the general site skips by someone , designated to have a “ Duty of Care “
c) at the “ Household Waste “ re-cycling centre ,
d) by an “ Authorised Company “ using a system of waste transfer notes , ◄
58) the Heath & Safety at Work Act places the responsibility at work on :
a) the Employer ,
b) the Employee ,
c) both the Employer and Employee ,
d) the Main Contactor ,
59) Under the Heath & Safety at Work Act an Employer must ensure that :
a) the working conditions are appropriate and safety equipment is provided , ◄
b) Employees take reasonable care of themselves and others as a result of work activities ,
c) employees co-operate with an employer and do not interfere with or misuse safety equipment ,
d) that plant and equipment is properly maintained , ◄
60) Under the Heath & Safety at Work Act Employees must ensure that :
a) the working conditions are appropriate and safety equipment is provided ,
b) they take reasonable care of themselves and others as a result of work activities , ◄
c) they co-operate with an Employer and do not interfere with or misuse safety equipment , ◄
d) plant and equipment is properly maintained ,

 

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Proving Unit :-

Switch ON ,
Insert probe ends of Testing Device into A.C./D.C. Outlet Sockets and while holding Testing device apply a light pressure in direction of Sockets ,
Switch OFF ,
Withdrawal of Testing Device instantly De-Energises ( form the Proving Unit )
Proof Testing ,
With Probes of Testing Device Inserted into Sockets APPLY SUFICIENT PRESURE for Good Electrical Contact ,
CHECK ∆ INDICATES AT ALL TIMES During Testing , Replace Battery if , in Normal Use , it Does NOT Iluminate , ◄

Check ALL NEON LAMPS Located within the Testing Device Iluminate for Duration of PROOF TESTING ,◄

( Remember that -&-s will ask about : Read Instructions Before Use/Operating )

 

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Proving Unit :-

To Deter ANYONE from RECNNECTING the Supply , a NOTICE must be FIXED on the Isolating SAYING “ Danger – Electrician at Work
Which you should Practice in the Workshop Under the Guidance of your Tutor or at Work Under the Guidance of your Supervisor , Electrical Isolation is an Important Safety Procedure ,

Select an Approved Test lamp or Voltage Indicating device , ▼
Verify that the Device is Functioning Correctly on a Known Supply or Proving Unit , ▼
▼ Satisfactory ? →→ No ► ( Replace or Repair )
Yes :
Locate and Identify Circuit or Equipment to be Worked Upon
Is the Circuit or Equipment in Service ? →→ No ►( Establish where and why it was De Energised )
Yes :
Identify Means of Isolation ▼
Ensure Isolation of the Circuit or Equipment by ▼
- Switching Off .
- Withdrawing Fuses .
- Locking off Isolating Switches or MCBs , ▼
Verify that the Circuit or Equipment to be Worked Upon is DEAD Using a Voltage Indicating Device Testing between :- ▼
Line / and Earth ,
Line / and Neutral ,
Neutral and Earth , ▼
Yes :
Satisfactory ? →→ DEAD ► Fit WARNING Signs , Recheck that the Voltage Indicating Device is Functioning Correctly on a Know Supply or Proving Unit , ▼
▼ Satisfactory ? Yes ( Begin Work ) No ► Replace or Repair and go Through the Procedure Again :
LIVE ~ ~ ~
Discover why with CARE and go Though the Procedure Again ,

 

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Circuit Diagram :
A Circuit Diagram shows most Cleary how a Circuit Works, All the Essential Parts and Connections are Rep-resented by their Graphical Symbols . The Purpose of a Circuit Diagram is to Help our Understanding of the Circuit , it will be Laid Out as Clearly as Possible , without regards to Physical Layout of the Actual Components and , Therefore , it may Not Indicate the most Convenient way to Wire-a-Circuit ,

Symbols and Multiples for Use with SI Units :
Prefix : Mega , Symbol : M , Multiplication Factor : x 10/6 or x 1000000 ,
Prefix : Kilo , Symbol : k , Multiplication Factor : x 10/3 or x 1000 ,
Prefix : Hecto , Symbol : h , Multiplication Factor : x 10/3 or 100 ,
Prefix : Decca , Symbol : da , Multiplication Factor : x 10 or x 10 ,
Prefix : Deci , Symbol : d , Multiplication Factor : x 10_1 or ÷ 10 ,
Prefix : Centi , c , Multiplication Factor : x 10_2 or ÷ 100 ,
Prefix : Milli , m , Multiplication Factor : x 10_3 or ÷ 1000 ,
Prefix : Micro , m , Multiplication Factor : x 10_6 or ÷ 1000000 ,

An Electric Fan-Heater was found to Take 10A when Connected to the 230V Mains Supply , Calculate the Résistance of the Heater Element :- ??
From ( R ) = V/I ( Ω ) ◄► ( R = 230 ÷ 10A = 23Ω ) The Heater Element Résistance is 23Ω

Calculate the Current Flowing in a Disco “ Sound and Light “ Unit having a Résistance of ( 57.5Ω ) when it is Connected to the 230V Electrical Mains ,
From ( I ) = V/R ( A ) ◄► ( I = 230V ÷ 57.5Ω = 4A ( The “ Sound and Light “ Unit takes 4 Amps ,

Resistivity :
“ Remember “ ► The Résistance or Opposition to Current Flow Varies , Depending Upon the Type of Material being Used to Carry the Electric Current ,

Using these Values we can Calculate the Résistance of Different Materials Using the Formulae !!!
Résistance ( R ) = pL / a ( Ω )
Where ( p ) ( the Greek Letter rho ) is the Resistivity Value for the Mater , ( l ) is the Length and ( a ) is the Cross-Sectional Area ,
( just for talk sake ) Copper : Resistivity ( Ωm ) 17.5 x 10-9
( just for talk sake ) Aluminum : Resistivity ( Ωm ) 28.5 x 10-9

* Calculate the Résistance of 100m of 2.5mm2 Copper Cable Using the Resistivity Values ,
We know that ( R ) = pL / a . Ω
Therefore ( R ) = 17.5 x 10-9 x 100 ……. 2.5 x 10-6
Therefore R = 700 x 10-3 ( Ω ) or
R = 700 ( mΩ )

Note : the Cross-Section of the Cable is in mm2 ( mm = 10-3 so, ) mm x mm = 10-6
* Calculate the Résistance of 100m of 2.5mm2 Aluminum Cable Using the Resistivity Values ,
We know that ( R ) = pL / a . Ω
Therefore ( R ) 28.5 x 10-9 x 100 ……. 2.5 x 10-6
Therefore R = 1140 x 10-3 ( Ω ) or
R = 1140 ( mΩ )

 

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So , if -&- Ask you about :-
Syllabus : Consider Weight , Mass , Force and Work done by a Force so let us Define some of these Scientific Term ,
Mass : this is a Measure of the Amount of Material in a Substance such as Wood or Metal ,
Weight : this is a Measure of Force which the Mass Exerts , it Exerts this Force because it is being Attracted towards the Earth by Gravity ,
Force : The Presence of a Force can Only be Detected by its Effect on an Object , A Force may Cause a Stationary Object to Move or a Moving Object to Stop ,
Gravity : The Force of Gravity Acts toward the Centre of the Earth and Causes Objects to Fall to the Ground at a Rate of ( 9.81 m/s )
Work Done : the Work done by Force is a Measure of the Force Exerted Time the Distance Moved in the Direction of the Force ,

Suppose a Broken-Down Car was to be Pushed along a Road ; Work would be Done on the Car by Applying the Force Necessary to Move it Along the Road , Heavy Breathing and Perspiration would be Evidence of Work Done !!!!!!!!!

Work Done = Force x Distance Moved in the Direction of the Force ( J )
The SI Unit of Work Done is the Newton Metre or Joule ( Symbol J )
Example ;
A Building Hoist Lift ten 50kg bags of Cement through a Vertical Distance of 30m to the Top of a High Rise Building , Calculate the Work Done by the Hoist , Assuming the Acceleration due to Gravity to be 9.81 m/s-2 ,
Work done = Force x Distance moved ( J )
But, Force = Mass x Acceleration ( N )
Therefore : Work done = Mass x Acceleration
x Distance Moved ( J )

work done = 10 x 50kg x 9.81m/s-2 x 30m
work done = 147.15kJ ,

 

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[FONT=IIFPD I+ Gill Sans]RCDs for protecting people have a rated tripping current (sensitivity) of not more than 30 milliamps (mA). Remember: [/FONT]
* an RCD is a valuable safety device,
* if the RCD trips, it is a sign there is a fault. Check the system before using it again;
* if the RCD trips frequently and no fault can be found in the system, consult the manufacturer of the RCD;
* the RCD has a test button to check that its mechanism is free and functioning. Use this regularly.

Use of 110V or 230V Equipment and Supplies : Q/A .

For Many Years , the Use of 110V CTE , ( Centre Tap Earthed ) has been Encouraged in Harsh Environments such as Construction Sites , This was Largely a UK Initiative , but in the rest of Europe , Systems of Working with 230V have been Established . if Responsible Individuals decide to Stipulate that Reduced Voltage is to be Used it must be made Clear that the Requirement is Dependant on the Environment and is therefore a Site Decision , the Use of 110V CTE , and Other Low-Voltage Systems in the UK is NOT Compulsory Under the Law but has been Recognised as Good-Practice in Harsh Environments , Guidance on Reduced Low Voltage Systems and Extra Low Voltage Systems is Provided in BS-7671

 

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The Regulations affecting RCD protection
Rule 411.3.3
Additional protection by means of a 30mA RCD is to be provided for all socket outlets with a rated current not exceeding 20A for use by ordinary persons. The only exceptions allowed are for socket outlets for use under the supervision of ‘skilled’ or ‘instructed persons’ e.g. some commercial/industrial locations, or a specifically labelled socket provided for connection of a particular item of equipment, such as a freezer.

Rule 710.411.3.3
In specific locations such as those containing a bath or shower there is now a requirement to provide RCD protection on all circuits, including lighting and shower circuits.

Rule 314.1 & 2
Every installation should be provided into circuits as necessary to avoid danger and minimise inconvenience in the event of a fault. Designers are required to reduce the possibility of unwanted RCD tripping due to excessive protective conductor currents but not due to an earth fault.
Separate circuits may be required for parts of the installation which need to be separately controlled in such a way that they are not affected by the failure of other circuits. The appropriate subdivision should take account of any danger arising from the failure of a single circuit, for example and RCD trip causing the disconnection of an important lighting circuit.

Regulation 522.6.7
Much greater use of RCDs is required to protect wiring concealed in walls or partitions, even where this is installed in previously defined Safe Zones.
This effectively means that all concealed wiring at a depth of less than 50mm from the surface now requires protection by a 30mA RCD unless provided with earthed mechanical protection.

 

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HSE Guidance
To comply with Regulation 13 of the Electricity at Work Regulations, precautions need to be taken on equipment that has been made dead. this includes securing the means of disconnection in the OFF position, putting a notice or label at the point of disconnection, and proving dead at the point of work using proprietary voltage detectors.

To comply with Regulation 14 of the Electricity at Work Regulations, dead working should be the normal method of carrying out work on electrical equipment or circuits. Live working should only be carried out in particular circumstances where it is unreasonable to work dead, such as some fault finding and testing, where the risks are acceptable, and where suitable precautions can be taken against injury. The pressure to carry out live work is becoming more common in areas such as construction sites, high-cost manufacturing and in retail outlets operating twenty-four hours per day. The requirements of the Regulations still apply in such situations and live working should only be carried out when justified using the criteria explained

Proving Dead Isolated Equipment or Circuits
Following isolation of equipment or circuits and “ BEFORE “ starting work it should be “ PROVED “ that the parts to be worked on and those nearby, are dead. It should “ NEVER BE ASSUMED “ that equipment is “ DEAD “ because a particular isolation device has been placed in the off position.

The procedure for proving dead should be by use of a proprietary test lamp or two pole voltage detector as recommended in HSE Guidance Note GS38, Electrical test equipment for use by electricians. Non-contact voltage indicators ( VOLTAGE STICKS) and “ MULTI-METERS “ should “ NOT BE USED “ . The test instrument should be proved to be working on a known live source or proprietary proving unit before and after use. All PHASES of the SUPPLY and the NEUTRAL should be tested and proved dead.

Safe Systems of Work
The employer must ensure that all employees involved in work on electrical equipment are competent and are instructed on safe systems of work, have been issued with written rules and instructions, and have access to, and use, appropriate locking-off devices, caution notices, a proprietary voltage detector and, where appropriate for the type of voltage detector being used, a proving unit.

 

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Type of Electrical Circuits :-
There are three main types of circuits encountered in a domestic situation. They are Ring Circuits, Radial Circuits and Lighting Circuits.

 

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* Electric Shock Occurs when a Person become Part of the Electrical Circuit :

To Prevent People Receiving an Electric Shock Accidentally , all Circuits must contain Protective Devices and all Exposed Metal must be Earthed ,
- All Circuits must be Electrically Isolated before any Work is Carried Out ,
- Electrical Isolation is an Important Safety Procedure ,
* the IEE Regulations tell us that Every Circuit must be Provided with Means of Isolation ,
* the Electricity at Work Regulations tell us that before Work Commences on Electrical Equipment it must be Disconnected from the Source of Supply and that the Disconnection must be Secure ,

Three-Effects of an Electric Current :-
When an Electric Current flows in a Circuit it can have One or More of the following Three-Effects : Heating : Magnetic or Chemical
* Heating Effect :-
* The Electrons moving in the Conductor causes the Conductor to Heat Up
* The Amount of Heat Generated depends upon the :
1) Amount of Current Flowing ,
2) Dimensions of the Conductors ,
3) Type of Conductor Material Used ,

* Practical Applications of the Heating Effect of an Electric Current are :-
1) Radiant Heaters which Heat Rooms ,
2) Circuit Protection Fuse and MCBs which Cut off the Supply when an Overcurrent Flows ,

Magnetic Effect :-
* Whenever a Current Flows in a Conductor a Magnetic Field is Set Up around the Conductor like an Extension of the Insulation ,
* Increasing the Current Increases the Magnetic Field ,
* Switch the Current off Causes the Magnetic Field to Collapse ,
* Practical Applications of the Magnetic Effect are :-
1) Electric Motors which Rotate because of the Magnetic Flux Generated by the Electrical Supply door Chimes and Buzzers which ding dong or buzz because of the Magnetic Flux Generated by the Electrical Supply ,

Chemical Effect :-
* When an Electric Current Flows though a Conducting Liquid , the Liquid Separates into its Chemical Parts , a Process called Electrolysis ,
* Alternatively , if two Metals are Placed in a Conducing Liquid they React Chemically and Produce a Voltage ,
* Practical Applications of the Chemical Effect are :-
1) Industrial Processes such as Electroplating which is Used to Silver Plate Sports Trophies and Cutlery ,
2) Motor Car Batteries which Store Electrical Energy ,

Three-6Ω Resistors are Connected in Series :- ( for any Series Connection )
Resistors in Series , Rt = R1 + R2 + R3 ,
Rt = 6Ω + 6Ω + 6Ω = 18Ω
Total Current It = Vt – Rt
Therefore :- It = 12V - 18Ω = 0.67A

The Voltage Drop across ( R1 is )
V1 = It x R1
Therefore :- V1 = 0.67A x 6Ω = 4V
The Voltage Drop across ( R2 is )
V2 = It x R2
Therefore :- V2 = 0.67A x 6Ω = 4V
The Voltage Drop across ( R3 is )
V3 = It x R3
Therefore :- V3 = 0.67A x 6Ω = 4V
I1 / R1 - 6Ω
I2 / R2 - 6Ω
I3 / R3 - 6Ω
It ( Vt = 12V )

 

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Resistors in Parallel :-
For any Parallel Connection , ( 1/Rt = 1/R1 + 1/R2 + 1/R3 )
Therefore :- 1/Rt = 1/6Ω + 1/6Ω + 1/6Ω

1/Rt = 1 + 1 + 1 = 3… 6Ω
Rt = 6Ω ÷ 3 = 2Ω
Total Current It = Vt/Rt , therefore :- It = 12V ÷ 2Ω = 6A
The Current flowing through ( R1 is )
I1 = Vt/R1 , therefore :- I1 = 12V ÷ 6Ω = 2A
The Current flowing through ( R2 is )
I2 = Vt/R2 , therefore :- I2 = 12V ÷ 6Ω = 2A
The Current flowing through ( R3 is )
I3 = Vt/R3 , therefore :- I3 = 12V ÷ 6Ω = 2A

Component Parts of an Electrical Circuit :-

These Series and Parallel Resistors are Connected together to form an Electrical Circuit , so , what is an Electrical Circuit ?
An Electrical Circuit has the following Five Components :-
* a Source of Electrical Energy , this might be a Battery giving a D.C. ( direct current ) Supply or the Main Supply which is A.C. ( alternating current )
* a Source of Circuit Protection , this might be a Fuse or Circuit-Breaker which will Protect the Circuit from “ Overcurrent “
* the Circuit Conductors or Cables . these carry Voltage and Current to Power the Load ,
* a Means to Control the Circuit , this might be a simple On/Off Switch but it might also be a Dimmer or a Thermostat ,
* and a Load , this is Something which needs Electricity to make it Work , it might be a Electric Lamp , an Electrical Appliance , an Electric Motor or an i-pod

 

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A Transformer Feeds the 9.81kW Motor Driving the Mechanical Hoist , the Input Power to the Transformer was found to be 10.9kW
Find the Efficiency of the Transformer :- ?? ŋ = Power Out / Power Input x 100 ( ŋ = 9.81kW / 10.9kW x 100 = 90% )

Thus the Transformer is 90% Efficient ,
Note : that Efficiency has No Units , but is Simply Expressed as a Percentage ,

Electrical Transformers :-
A Transformer is an Electrical Machine without Moving Parts , which is Used to Change the Value of an Alternating Voltage ,
- a Transformer will Only Work on an Alternating Supply . it will NOT Normally Work from a D.C. Supply such as a Battery ,

Transformer : Consists of Two-Coils called the ( Primary and Secondary ) Coils or Windings , wound on to a Common Core , the Iron Core of the * * *Transformer is NOT Solid but Made Up of very Thin Sheets called ( Laminations ) to Improve Efficiency ,
* an Alternating Voltage Applied to the Primary Winding Establishes an Alternating Magnetic Flux in the Core ,
* the Magnetic Flux in the Core causes a Voltage to be Induced in the Secondary Winding of the Transformers ,
* the Voltage in both the ( Primary and Secondary ) Windings is Proportional to the Number of Turns ,
* this Means that if you Increase the Number of Secondary Turns you will Increase the Output Voltage , this has an Application in Power Distribution ,
* Alternatively , Reducing the Number of Secondary Turns will Reduce the Output Voltage , this is Useful for ( Low-Voltage-Supplies ) such as Domestic bell Transformers’ , because it has NO Moving Parts , a Transformer can have a Very High Efficiency , Large Power Transformers , Used on
Electrical Distribution Systems , can have an Efficiency of Better than 90% ,

These Power Transformers need ( Cooling ) to take the ( Heat ) Generated away from the ( Core ) this is Often Achieved by Totally Immersing the Core and Windings in Insulating ( Oil )

Very Small Transformers are Used in Electronic Applications , Small Transformers are Used as Isolating Transformers in ( Shaver Sockets ) and can be Used to Supply ( SELV ) separated extra low voltage , Sources , Equipment Supplied from a SELV Source may be Installed in a Bathroom or Shower room , Provided that it is Suitably Enclosed and Protected from the ( Ingress of Moisture ) this includes Equipment such as Water Heater , Pumps for Showers and Whirlpools Baths ,

 

[brucelee]

Thanks mr leaf
great work will be a great help

 

[amberleaf]

Q : What is the Voltage of the Neutral Terminal ?
A : it stays as a Potential Close to Zero with Respect to Earth ,

Q : What should be done to Appliances with Metal Cases ?
A : They are Usually Earthed ,

Q : Describe how the Résistance of a Thermistor changes as the Temperature Increases ?
A : it Decreases ,

Q : For Components Connected in Series , what do you know about the Total Potential Difference ?
A : The Potential Difference of the Supply is Shared between the Components According to their Résistance – Bigger Résistance – Bigger Share ,

Q : What is the Voltage of the Live Terminal ?
A : The Live Terminal of the Mains Supply Alternates between Positive and Negative Potential with Respect to the Neutral Terminal ,

Q : For Components Connected in Parallel , what do you know about the Current Through Them ?
A : The Total Current through the Whole Circuit is Equal to the Sum of the Currents through the Separate Components – and the Lower the Résistance if the Component , the More the Current Flows ,

Q ; For Components Connected in Parallel , what do you know about the Potential Difference Across each Component ?
A : it is the Same ,

Q :What Type of Current do Cells and Batteries Supply ?
A : Direct Current ( d.c. )

Q : for Components Connected in Series , what do you know about the Current through each Component ?
A : it is the Same ,

Q : for Components Connected in Series , how do you Calculate the Total Résistance ?
A : The Total Résistance is the Sum of the Résistance of Each Component ,

Q : How do you know what Value of Fuse to put in an Appliance’s Plug ?
A : From the Power and the Voltage we can Calculate the Current and the Fuse it Needs ,

Q : What is Résistance ?
A : The Ratio of Potential Difference across a Component to the Current Flowing through it ,

Q : What happens when an Electrical Charge Flows through a Resistor ?
A : Electrical Energy is Transformed into Heat Energy ( it get Hot )

Q : What does the Size of the Current in a Circuit Depend on ?
A : How hard the Supply tries to Push Charge through the Circuit and how hard the Circuit Resists having Charge Pushed through it ,

Circuit Basics :-
All Electrical Circuits Require three-Elements ,
1) A Source Voltage , that is , an Electron Pump usually a Battery or Power Supply , ( Energy In )
2) A Conductor to Carry Electrons from and to the Voltage Source ( Pump ) the Conductor is often a Wire , ( Energy Transfer )
3) A load or Résistance , A Point where Energy is Extracted form the Circuit in the Form of Heat , Light , Motion , etc. ( Energy Out )

Potential Changes of Current in a Circuit :-
High Energy Current ► Résistance ( Potential Drop ) Low Energy Current ► ,
High Energy Current ◄ Voltage Source ( Potential Rise ) Low Energy Current ◄

Measureable Quantities that can be Obtained from an Electrical Circuit :-
1) Voltage Rise – Measures the Energy given to Electrons as they leave a Voltage Source , it is Measured in Volts ( + )
2) Voltage Drop - Measures the Energy lost by to Electrons when they leave a Résistance , it is Measured in Volts ( - )
3) Current - Measures the Flow Rate through a Conductor , it is Measured in Amperes ( AMPS )
4) Résistance - Measures the Opposition to Current Flow through a Conductor or Resistor , it is Measured in Ohms ( its Symbol . is Omega )

Voltage Sources and Internal Resistance :-
1) All Voltage Sources contain Internal Résistance , that is Resistance that is Part of the Voltage Producing Device itself which cannot be Eliminated ,
2) The Voltage that the Device ( Battery for Example ) could Produce if no Internal Résistance was Present is called its ( EMF ) stands for Electromotive Force – the Force that moves the Electrons ,
3) The Useable Voltage which is Available to the Circuit after the Internal Résistance Consumes its Share of the ( EMF ) is Called the Terminal Voltage ,

 

[amberleaf]

Q: What are the advantages of star-delta starter with induction motor ?
A 1). The main advantage of using the star delta starter is reduction of current during the starting of the motor. Starting current is reduced to 3-4 times Of current of Direct online starting.(2). Hence the starting current is reduced , the voltage drops during the starting of motor in systems are reduced.