Introduction to Number System
The number of digits in the system determines the base of any number system, such as decimal and binary. Basically binary is a base-2 number system as it uses two basic digits. Thus it means that the whole Binary number system depends on the two basic digits. Whereas Decimal is a base-10 system since it uses ten digits, and these are 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9.
Decimal Number System
A system with base-10 is a decimal number system. Thus it means that there are ten basic digits on which the decimal number system depends. The digits are 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9. By using these ten digits all the numbers in decimal number system are written. Thus the place value of a digit in a number increases the power from right to left. For example, the following are the place value of each digit of number 5471: The place value of 1 is: 1*100 =1 The place value of 6 is: 7*101 =70 The place value of 3 is: 4*102 =400 The place value of 5 is: 5*103 =5000
Binary Number System
A number system with a base-2 is known as binary number system. The whole binary number system depends on two digits these are 0 and 1, respectively. By using these two digits the numbers in binary number system are written. Thus the place value of a digit in a number increases in the power of 2 from right to left. The following example shows the place value of each digit in the number 101010 should be 010101 The place value of 1 is: 1*20 = 1 The place value of 0 is: 0*21 = 0 The place value of 1 is: 1*22 = 4 The place value of 0 is: 0*23 = 0 The place value of 1 is: 1*24 = 16 The place value of 1 is: 0*25 = 0
Hexadecimal Number System
The hexadecimal number system is based on 16. It means, there are 16 basic digits on which whole hexadecimal number system depends. The digits are 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12,13,14 and 15, where as the numbers 10, 11,12, 13, 14 and 15 are also represented as A, B, C, D, E and F. By using these 16 digits all the numbers in Hexadecimal number system are written. Thus the place value in hexadecimal system is increased in the power of 16 from right to left. The following example shows the place value of each digit in the number 121FA: Place value of A is: 10*160 =10 Place value of F is: 15 *161 =240 Place value of 6 is: 1*162 = 256 Place value of 2 is: 2*163 =8192 Place value of 1 is: more... 
Types of Computer
There are three types of computer including digital computers/analog computers and hybrid computers.
Digital Computer
The digital computer stores data, such as text and picture in the form of numbers and proceed in discrete steps from one state to the next. The state of a digital computer involves binary (Os and Is) digit. All operations are carried out on those digits at extremely fast rates. Digital computer can be further classified in the purpose wise and size and performance wise.
Analog Computer
Analog computers use continuous physical properties for calculations. An analog magnetic tape, for example, manipulates magnetism to record sound. The magnetic imprint on the tape is a direct analog of the sound, and is read back by a reader. An analog computer uses physical properties in the same way. Analog computers have been built using mechanical, hydraulic, optical and electric principles.
Hybrid Computers
The hybrid computers combine the best quantities of both analog and digital computers. These types of computers operate by measuring rather than by calculating. It works with analog or continuous values. Computations are carried out with physical quantities such as temperature, length and voltage. These types of computers are used for measurement of patient's blood pressure, heart beat and the operation is carried out in digital to monitor patient's initial sign.
Which of the following statements is true about microcomputer?
(A) Microcomputer is faster than minicomputers
(B) Microcomputer is a computer whose CPU (Central Processing Unit) is a microprocessor
(C) Microcomputer can be categorized as desktop, workstation and programmable
(D) (B) and (C) are true (E) None of these
Answer: (D)
Explanation
Correct Option:
(D) The options (B) and (C) are true
Incorrect Option:
Rests of the options are invalid.
Computers are of three types: digital computers, analog computers and hybrid computers. Which one of the following types of computer is used for measurement of patient's blood pressure?
(A) Digital
(B) Analog
(C) Hybrid
(D) All of these
(E) None of these
Answer: (c)
Explanation
Correct Option:
(C) The hybrid computers are used for measurement of patient's blood pressure
Incorrect Option:
Rests of the options are invalid.
The precision of analog computers is limited to................
(A) One
(B) Two
(C) Three
(D) Five
(E) None of these
Answer : (c)
Explanation
Correct Option:
(C) The precision of analog computers is limited to three, or at most, four digits of precision.
Incorrect Option:
Rests of the options are invalid. 
Classification of Computer
Micro Computers
Micro Computer is a computer, whose CPU (Central Processing Unit) is a microprocessor. All components of the microprocessor are on a single integrated circuit chip.
It can also be categorized as following:
Mini Computers
They are faster than micro computers. Basically these are mainly multi-user systems, where many users work on the systems. Generally these types of computers possess larger memories and greater storage capacity.
Mainframe Computers
They are large and expensive machines. Generally they handle huge volumes of information and data. In terms of speed, they are having significant processing capacity. More than hundred users can support at a time. The ICL39 and IBM 3090/ 4300 are the examples of mainframe computers. 
Water Pollution
Water is a natural resource. A large number of substance are obtained from water. Apart from air, the most abundant source on earth is water. There are about 1.4 billion cubic kilometers of water on earth. About seventy one per cent surface of the earth is covered with water and is called hydrosphere.
The amount has not changed at all in the million year of earth's existence. There is plenty of water on our planet, but its distribution is not uniform. About 97.4% of the total water on the earth is present in oceans. Of the remaining 2.6%, only is in liquid form, the rest is frozen in polar caps and glaciers like those of the HIMALAYAS. If the surface of India were flat, and all the ice was packed on the surface of India, it would reach an incredible height of 9 km . thus, only 0.01% of the total water on the earth, which is available freshwater, is used by us and other living beings. The water in the oceans is so salty that it cannot be used for most purposes.
Sources of Water Pollution
Effect of Pollution on Water Bodies
Purification of Waste Water
Which one of the following is a cause of air pollution?
(a) Burning of fossil fuel
(b) Smokes from motor vehicles
(c) Volcano eruption
(d) All of these
(e) None of these
The water which is fit for drinking is called:
(a) Sewage
(b) Black water
(c) Potable water
(d) All of these
(e) None of these
Answer: (c)
Air Pollution
Air pollution is defined as the addition of undesirable materials into the atmosphere either due to human activities which adversely affect the quality of the air and hence life on earth or through natural process like volcano eruptions.
Causes of Air Pollution
Pollution
Our environment is our surrounding. It comprises all living and non living things. Any undesirable change in the physical, chemical or biological characters of air, water and soil leads to environmental pollution which is harmful to human beings directly or indirectly.
Pollutant
A pollutant is a substance that may be added to the environment directly or indirectly by man or natural events, to extent which adversely affects humans, animals, vegetation and other materials.. 
Lightning
Lightning is one of the most deadly natural phenomena known to man. The bright flash of light which we see in the clouds is called lightning. Lightning is an electric current. Within a cloud many small bits of ice bump into each other as they move around in the air. Due to these collisions electric charges are produced. The positive charges form at the top of the cloud and the negative charges form at the bottom of the cloud. When the amount of these charges becomes extremely large, then the electric charges start flowing with high speed through air between them as a result an intense spark of electricity is produced in the sky.
Earthquake
Earthquake is a destructive natural phenomenon which occurs due to sudden movements in earth7 crust. The shaking of the ground caused by sudden movements in earth's crust is known as earthquake. Earthquake sometimes causing great destruction. The intensity of an earthquake is measured by Richter scale. The place inside the earth's crust where the earthquake is generated is known as focus of the earthquake. The point on the earth's surface directly above the focus is called epicentre. The waves generated by an earthquake are called the seismic waves. The instrument which is used to measure and record the magnitude of an earthquake in terms of shockwaves is known as seismograph.
What type of force is experienced between two like charged particles?
(a) Force of attraction
(b) Force of repulsion
(c) No force is experienced
(d) All of these
(e) None of these
Answer: (b)
How many types of electric charges are there?
(a) One
(b) Two
(c) Three
(d) Four
(e) None of these
Answer: (b)
Electric Charge
Electric charge is a property of certain subatomic particles like electrons and protons that allows them to attract or repel other charged particles by electric force. This is the force which binds nucleus and electrons of an atom together.
Charges are of two kinds
(i) Negative charge
(ii) Positive charge
Like charged particles repels each other whereas unlike charged particles attract each other. Electrons are negatively charged particles whereas protons are positively charged particles. That is why between two electrons force of repulsion is experienced whereas between an electron and a proton, force of attraction is experienced. In other word 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 a proton placed at same distance apart is not repulsive but attractive in nature.
Charging by conduction and induction:
An object can be charged by the following ways:
(i) Charging by rubbing (friction)
(ii) Charging by induction
(iii) Charging by conduction
Electroscope
An electroscope is an instrument for detecting the presence of electric charge on an object. It consists of two thin metal leaves suspended from a metal hook. When the hook is brought near a source of electric charge, some of the electrons in the hook are pushed to the leaves (if the source is negative) or pulled up to the hook from the leaves (if the source is positive).. 
Chemical Effects of Electricity
In order to generate electricity there are many methods used, one of them is chemical. Remember batteries, where electricity is generated because of chemical reactions inside cell. Also in conductors like liquids and gases electricity is carried not by electrons as it is in solid constructions(copper, aluminium, etc.), but by ions - molecules with electric charges. Even non distilled water contain enough ions to be conductive. Lets go through several chemical effects of electricity.
Electrolysis: Electrolysis is a decomposition of liquid compound by passing electric current through liquid called electrolyte(salt water, copper sulphate, sulphuric acid). Electrolysis is used very widely in industry like electroplating of metals, refining of copper and extraction of aluminum from ore. To make electrolysis happen there are two conductors used cathode (-) and anode(+).
Electroplating: The process of covering a more reactive metal with a less reactive metal with the help of electricity is known as electroplating. Material to be plated should be connected as cathode while anode usually loses material.
Chemical Cell
According to this principal all batteries are generating electric power. Chemical cells converts chemical energy in to electrical. If there are two different conductors(eg. Copper and zinc) placed in electrolyte, electric current starts flowing between electrodes.
Each different pair of electrodes generate different potential. As long as there is an external circuit, electrons can flow through it from one electrode to another. Because zinc tends to lose electrons more readily than copper, zinc atoms in the zinc electrode lose electrons to produce zinc ions. The net result is that zinc metal reacts with copper ions to produce zinc ions and copper metal.
Non Rechargeable Lechlanche Cells
These are cells that generate about 1.5V of EMS, but if falls in continuous use due to polarization of electrode. These cells are better to us for intermittent purposes like torches, bells, indicators etc. These cells are cheap and has a shelf life about 2 years.
There are more dry cell technologies that enables to remain EMF constant for longer times. Ones are Mercury cells. These cells provide 1.3V for longer time than Lechlanche cells.
Rechargeable Cells
Rechargeable cells are most commonly used today as main factor - the price is becoming acceptable for everyone. And there is another practical approach - these cells can be recharged after use. In other words the conversion of chemical energy to electrical is reversible. There are many types of rechargeable cell technologies. Ones of common are lead-acid and the alkaline cells. These cells are usually used in cars.
Electric Current
An electric current is a movement of charge. When two objects with different charges touch and redistribute their charges, an electric current flows from one object to the other until the charge is distributed according to the capacitances of the objects. If two objects are connected by a material that lets charge flow easily, such as a copper wire, then an electric current flows from one object to the other through the wire. Electric current can be demonstrated by connecting a small light bulb to an electric battery by two copperwires. When the connections are properly made, current flows through the wires and the bulb, causing the bulb to glow.
Conductors and Insulators
Conductors are materials that allow an electric current to flow through them easily. Most metals are good conductors.
Substances that do not allow electric current to flow through them are called insulators, nonconductors, or dielectrics. Rubber, glass, and air are common insulators. Electricians wear rubber gloves so that electric current will not pass from electrical equipment to their bodies. However, if an object contains a sufficient amount of charge, the charge can arc, or jump, through an insulator to another object. For example, if you shuffle across a wool rug and then hold your finger very close to, but not in contact with, a metal doorknob or radiator, current will arc through the air from your finger to the doorknob or radiator, even though air is an insulator. In the dark/ the passage of the current through the air is visible as a tiny spark.
Measuring Electric Current
Electric current is measured in units called amperes (amp). If 1 coulomb of charge flows past each point of a wire every second, the wire is carrying a current of 1 amp. If 2 coulombs flow past each point in a second, the current is 2 amp.
Voltage
When the two terminals of a battery are connected by a conductor, an electric current flows through the conductor. One terminal continuously sends electrons into the conductor, while the other continuously receives electrons from it. The current flow is caused by the voltage, or potential difference, between the terminals.
Resistance
A conductor allows an electric current to flow through it, but it does not permit the current to flow with perfect freedom. Collisions between the electrons and the atoms of the conductor interfere with the flow of electrons. This phenomenon is known as resistance. Resistance is measured in units called ohms. The symbol for ohms is the Greek letter omega, W.
A good conductor more... 
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