Class VI August
POWER TOOL PRECAUTIONS
Tools are such a common part of our lives that it is difficult to remember that they may pose hazards. All tools are manufactured with safety in mind but, tragically, a serious accident often occurs before steps are taken to search out and avoid or eliminate tool-related hazards.
In the process of removing or avoiding the hazards, workers must learn to recognize the hazards associated with the different types of tools and the safety precautions necessary to prevent those hazards.
HAND TOOLS
Hand tools are non-powered. They include anything from axes to wrenches. The greatest hazards posed by hand tools result from misuse and improper maintenance.
Some examples:
In the process of removing or avoiding the hazards, workers must learn to recognize the hazards associated with the different types of tools and the safety precautions necessary to prevent those hazards.
HAND TOOLS
Hand tools are non-powered. They include anything from axes to wrenches. The greatest hazards posed by hand tools result from misuse and improper maintenance.
Some examples:
- Using a screwdriver as a chisel may cause the tip of the screwdriver to break and fly, hitting the user or other employees.
- If a wooden handle on a tool such as a hammer or an axe is loose, splintered, or cracked, the head of the tool may fly off and strike the user or another worker.
- A wrench must not be used if its jaws are sprung, because it might slip.
- Impact tools such as chisels, wedges, or drift pins are unsafe if they have mushroomed heads. The heads might shatter on impact, sending sharp fragments flying.
Power tools can be hazardous when improperly used. There are several types of power tools, based on the power source they use: electric, pneumatic, liquid fuel, hydraulic, and powder-actuated.
Employees should be trained in the use of all tools - not just power tools. They should understand the potential hazards as well as the safety precautions to prevent those hazards from occurring.
The following general precautions should be observed by power tool users:
Employees should be trained in the use of all tools - not just power tools. They should understand the potential hazards as well as the safety precautions to prevent those hazards from occurring.
The following general precautions should be observed by power tool users:
- Never carry a tool by the cord or hose.
- Never yank the cord or the hose to disconnect it from the receptacle.
- Keep cords and hoses away from heat, oil, and sharp edges.
- Disconnect tools when not in use, before servicing, and when changing accessories such as blades, bits and cutters.
- All observers should be kept at a safe distance away from the work area.
- Secure work with clamps or a vise, freeing both hands to operate the tool.
- Avoid accidental starting. The worker should not hold a finger on the switch button while carrying a plugged-in tool.
- Tools should be maintained with care. They should be kept sharp and clean for the best performance. Follow instructions in the user's manual for lubricating and changing accessories.
- Be sure to keep good footing and maintain good balance.
- The proper apparel should be worn. Loose clothing, ties, or jewelry can become caught in moving parts.
- All portable electric tools that are damaged shall be removed from use and tagged "Do Not Use."
- Electric tools should be operated within their design limitations.
- Gloves and safety footwear are recommended during use of electric tools.
- When not in use, tools should be stored in a dry place.
- Electric tools should not be used in damp or wet locations.
- Work areas should be well lighted.
- Keep all tools in good condition with regular maintenance.
- Use the right tool for the job.
- Examine each tool for damage before use.
- Operate according to the manufacturer's instructions.
- Provide and use the proper protective equipment.
Class VII August
Definition of Electrical terms
The electric charge is given by:
Q = I ∙ t
Corresponding SI units:
coulomb (C) = ampere (A) ∙ second (s)
Where I is the electric current and t is the time (duration).
Q = I ∙ t
Corresponding SI units:
coulomb (C) = ampere (A) ∙ second (s)
Where I is the electric current and t is the time (duration).
- Electric charge is a fundamental property like mass, length etc associated with elementary particles for example electron, proton and many more.
- Electric charge is the property responsible for electric forces which acts between nucleus and electron to bind the atom together.
- Charges are of two kinds
(i) negative charge
(ii) positive charge - Electrons are negatively charged particles and protons, of which nucleus is made of, are positively charged particles. Actually nucleus is made of protons and neutrons but neutrons are uncharged particles.
- Electric force between two electrons is same as electric force between two protons kept at same distance apart i. e., both set repel each other but electric force between an electron and proton placed at same distance apart is not repulsive but attractive in nature.
- (a) Like charges repel each other
- (b) Unlike charges attract each other
- Assignment of negative charge on electron and positive charge on proton is purely conventional; it does not mean that charge on electron is less than that on proton.
- Importance of electric forces is that it encompasses almost each and every field associated with our life; being it matter made up of atoms or molecules in which electric charges are exactly balanced or adhesive forces of glue associated with surface tension, all are electric in nature.
Unit
- Charge on a system can be measured by comparing it with the charge on a standard body.
- SI unit of charge is Coulomb written as C.
- 1 Coulomb is the charge flowing through the wire in 1 second if the electric current in it is 1A.
- Charge on electron is -1.602 * 10 -19 C and charge on proton is positive of this value.
- Two important properties of charge are Quantization and Conservation.
(a) Quantization of charge
(i) Electric charge can exist only as an integral multiple of charge on an electron (-e) i.e.
q = ± ne, where n is an integer.
(ii) The Possible values of electric charge are q = ± 1e; ± 2e; ± 3e...
(iii) Charge less than the charge on an electron (i.e. e = 1.6 * 10-19 C) is not possible.
(b) Conservation of charge
(i) On an isolated system, total electric charge always remains constant.
(ii) Total charge on a body is equal to the algebraic sum of all the charges present on it. Every atom is electrically neutral as it contains as many electrons as the number of protons in it.
(iii) When we rub a glass rod with a piece of silk, the positive charge acquired by the glass rod is equal to negative charge acquired by the silk piece. Thus charges are produced in equal and unlike pairs.
Example (1): What is the possible value of electric charge?
(a) 1 X 1.6 X 10-19 C
(b) 2.4 X 1.6 X 10-19 C
(c) -8 X 1.6 X 10-19 C
(d) 1 X 1.8 X 10-19 C
Solution: (a)
As we know that, electric charge can exist only as an integral multiple of charge on an electron (-e) i.e.
q = ±ne, where n is an integer. So q = ±1 X 1.6 X 10-19 C
Example (2): If n=2, what will be the value of electric charge? (Given e =1.6 X 10-19 C)
(a) ±0.8 X 10-19 C
(b) ±3.2 X 10-19 C
(c) ±4.3 X 10-19 C
(d) ±6.3 X 10-19 C
Solution: (b)
We know that
q = ±ne
= 2 X 1.6 X 10-19 C
= ±3.2 X 10-19 C
Hence option (b) is correct.
Example (3): Is charge less than the charge (i.e. e = 1.6 X 10-19 C) on an electron possible?
(a) Yes (b) No
Solution :( b) As we know
q = ±ne where n is an integer i.e. n= 1, 2, 3,...
Example 4): What is the total charge of all of the protons in 1.00 kg of carbon?
(a) 4.82 X 107 C
(b) 3.96 X 107 C
(c) 4.82 X 109 C
(d) 3.96 X 1012 C
Solution: (a) We can find the number of coulombs of positive charge there are in 1.00 kg of carbon from Q=6nce, where nc is the number of atoms in 1.00 kg of carbon and the factor of 6 is present to account for the presence of 6 protons in each atom. We can find the number of atoms in 1.00 kg of carbon by setting up a proportion relating Avogadro’s number NA , the mass of carbon, and the molecular mass of carbon to nc.
Example 5): Determine the electric current in an electric circuit where the total electric charge is 6 C over 5 seconds.
Isolating I from Q = I ∙ t
I = Q/t = 6 / 5 = 1.2 A
I = Q/t = 6 / 5 = 1.2 A
Electric Potential and Potential Difference
'Electrical potential' is a condition, which determines the direction of the flow of charge.
Let us consider the experiment outlined below to understand electrical potential.
Pipe A is connected to the container B through a stopcock. The quantity of water in A is less than the quantity in B, but the level of water is higher than the level in B.
When the stopcock is opened, this water begins to flow from A to B, till the levels of water in both A and B are equal.
The above observation, determines that it is not the quantity of water, but the level of water, which decides the direction of flow of water. Here the water in 'A' is at a higher 'gravitational potential' and the water in 'B' is at a lower gravitational potential. It is the 'potential difference' that is responsible for the flow of water.
Similarly 'electrical potential' is the direction of the flow of charge.
Let us consider the process of depositing an electric charge, for example, a positive charge on a neutral body. Initially it acquires a small amount of charge. If we wish to deposit some more charge of the same type on that body, it will experience a force of repulsion due to the charges already present on it. Therefore, work has to be done to counter this force of repulsion. This work done on the electrical charge in the process of charging gets stored as potential energy of charges. This is known as 'electrostatic potential'.
August Class VIII
House wiring
Introduction
A network of wires drawn connecting the meter board to the various energy consuming loads (lamps, fans, motors etc) through control and protective devices for efficient distribution of power is known as electrical wiring.
Electrical wiring done in residential and commercial buildings to provide power for lights, fans, pumps and other domestic appliances is known as domestic wiring. There are several wiring systems in practice. They can be classified into:
v Types of Wiring:
- Cleat wiring
- CTS wiring or TRS wiring or batten wiring
- Metal sheathed wiring or lead sheathed wiring
- Casing and capping
- Conduit wiring
1. Cleat wiring:
In this type of wiring, insulated conductors (usually VIR, Vulcanized Indian Rubber) are supported on porcelain or wooden cleats. The cleats have two halves one base and the other cap. The cables are placed in the grooves provided in the base and then the cap is placed. Both are fixed securely on the walls by 40mm long screws. The cleats are easy to erect and are fixed 4.5 – 15 cms apart. This wiring is suitable for temporary installations where cost is the main criteria but not the appearance.Advantages:
- Easy installation
- Materials can be retrieved for reuse
- Flexibility provided for inspection, modifications and expansion.
- Relatively economical
- Skilled manpower not required.
Disadvantages:
- Appearance is not good
- Open system of wiring requiring regular cleaning.
- Higher risk of mechanical injury.
/ Batten wiring:
In this wiring system, wires sheathed in tough rubber are used which are quite flexible. They are clipped on wooden battens with brass clips (link or joint) and fixed on to the walls or ceilings by flat head screws. These cables are moisture and chemical proof. They are suitable for damp climate but not suitable for outdoor use in sunlight. TRS wiring is suitable for lighting in low voltage installations
Advantages:
- Easy installation and is durable
- Lower risk of short circuit.
- Cheaper than casing and capping system of wiring
- Gives a good appearance if properly erected.
Disadvantages:
1. Danger of mechanical injury.
2. Danger of fire hazard.
3. Should not be exposed to direct sunlight.
4. Skilled workmen are required.
3. Metal Sheathed or Lead Sheathed wiring :
The wiring is similar to that of CTS but the conductors (two or three) are individually insulated and covered with a common outer lead-aluminum alloy sheath. The sheath protects the cable against dampness, atmospheric extremities and mechanical damages. The sheath is earthed at every junction to provide a path to ground for the leakage current. They are fixed by means of metal clips on wooden battens. The wiring system is very expensive. It is suitable for low voltage installations.
Precautions to be taken during installation
- The clips used to fix the cables on battens should not react with the sheath.
- Lead sheath should be properly earthed to prevent shocks due to leakage currents.
- Cables should not be run in damp places and in areas where chemicals (may react with the lead) are used.
Advantages:
- Easy installation and is aesthetic in appearance.
- Highly durable
- Suitable in adverse climatic conditions provided the joints are not exposed
Disadvantages:
- Requires skilled labor
- Very expensive
- Unsuitable for chemical industries
4. Casing and Capping:
It consists of insulated conductors laid inside rectangular, teakwood or PVC boxes having grooves inside it. A rectangular strip of wood called capping having same width as that of casing is fixed over it. Both the casing and the capping are screwed together at every 15 cms. Casing is attached to the wall. Two or more wires of same polarity are drawn through different grooves. The system is suitable for indoor and domestic installations.
Advantages:
- Cheaper than lead sheathed and conduit wiring.
- Provides good isolation as the conductors are placed apart reducing the risk of short circuit.
- Easily accessible for inspection and repairs.
- Since the wires are not exposed to atmosphere, insulation is less affected by dust, dirt and climatic variations.
Disadvantages:
- Highly inflammable.
- Usage of unseasoned wood gets damaged by termites.
- Skilled workmanship required.
5. Conduit wiring:
In this system PVC (polyvinyl chloride) or VIR cables are run through metallic or PVC pipes providing good protection against mechanical injury and fire due to short circuit. They are either embedded inside the walls or supported over the walls, and are known as concealed wiring or surface conduit wiring (open conduit) respectively. The conduits are buried inside the walls on wooden gutties and the wires are drawn through them with fish (steel) wires. The system is best suited for public buildings, industries and workshops.
Advantages:
- No risk of fire and good protection against mechanical injury.
- The lead and return wires can be carried in the same tube.
- Earthing and continuity is assured.
- Waterproof and trouble shooting is easy.
- Shock- proof with proper earthing and bonding
- Durable and maintenance free
- Aesthetic in appearance
Disadvantages:
1. Very expensive system of wiring.
2. Requires good skilled workmanship.
3. Erection is quiet complicated and is time consuming.
4. Risk of short circuit under wet conditions (due to condensation of water in tubes).
Energy Meter
Terminals | Note |
1 | Inlet phase line |
3 | Inlet neutral line |
4 | Outgoing neutral line |
5 | Outgoing phase line |
Class IX : Electromagnetisim
Electromagnetism
The term "magnetic effect of current" means that "a current flowing in a wire produces a magnetic field around it". The magnetic effect of current was discovered by Oersted in 1820. Oersted found that a wire carrying a current was able to deflect a magnetic needle. Now, a magnetic needle can only be deflected by a magnetic field. Thus it was concluded that a current flowing in a wire always gives rise to a magnetic field round it. The magnetic effect of current is called electromagnetism which means that electricity produces magnetism.
Faraday's Magnetic Field Induction Experiment
When Michael Faraday made his discovery of electromagnetic induction in 1831, he hypothesized that a changing magnetic field is necessary to induce a current in a nearby circuit. To test his hypothesis he made a coil by wrapping a paper cylinder with wire. He connected the coil to a galvanometer, and then moved a magnet back and forth inside the cylinder.
When you move the magnet back and forth, notice that the galvanometer needle moves, indicating that a current is induced in the coil. Notice also that the needle immediately returns to zero when the magnet is not moving. Faraday confirmed that a moving magnetic field is necessary in order for electromagnetic induction to occur.
The Left Hand Rule
It is well know that a current carrying conductor in a magnetic field experiences a force, and that if a conducting loop of wire moves relative to a magnetic field, a current is generated. Fleming's Left Hand Rule enables us to calculate the direction of the force in the first case and the direction of the field in the second case. This is illustrated below.
In this diagram the two fingers are horizontal at right angles and the tunmb is vertical and at right angles to both. In fact, first finger, second finger and thumb are all at right angles to each other.The Right Hand Grip Rule
A current also produces a magnetic field. The magnetic field will loop around the conductor. We can find the sense in which it loops by gripping the conductor carrying the current in our right hand. The fingers will point in the direction of the field. This shown below to the left. We can also apply it to solenoids, in a sense, backwards. If the fingers point in the direction of the current, the thumb will point AGAINST the magnetic field.
Class X House wiring
