10th Class

       Electric Motors   Electric motor is a device which converts electrical energy into mechanicalenergy. It works on the principle that when a current carrying conductor isplaced in the magnetic field it exerts a force on it and the coil rotatescontinuously as long as the current flows through it. It consists of a rectangular coil PQRS. It is placed between the poles of the magnetic field in such a way that the arms PQ and RS are perpendicular to the direction of the magnetic field. The ends of the coil are connected to the two halves A and B, of the split ring. The inner sides of these split ring are insulated and attached to an axle. The external conducting edges of A and B touches two conducting stationary brushes U and V, as shown in the figure given below. more...

        Force on Current Carrying Conductor   So far we have learnt about the current flowing through a conductor produces magnetic effect. The reverse of this is also true. A magnet exerts a mechanical force on a current carrying conductors when it is placed in the magnetic field and produces motion in the conductor. The various devices like motors, generators, fan etc. works on this principle. We can demonstrate this with the help of the following activity given below:

         Electromagnet   Electromagnet is the magnet which is produced by passing electric current through the magnetic material. It consists of long coil of insulated copper wire wound on a soft iron core. The core of the electromagnet is a soft iron core, which gets strongly magnetized when the electric current is passed through it and easily get demagnetized if the current is switched off. But if other material is used for this purpose, it will not loose its magnetism instantly when we switch off the electric current. There are some factors which affects the strength of the electromagnet.   The factors are:

• The number of turns in the coil. If we increase the number of turns in the coil, the strength of the electromagnet also increases.
• The strength of current flowing through the wire. If we increase the more...

       Introduction   There are various effects of electric current. One of such effect we have studiedin the previous chapter of electricity. One of the other effect of electric currentis the magnetic effect of electric current. We will study about the magneticeffect produced by the electric current flowing through the wire. Let us take astraight copper wire and place it between the point A and B in an electriccircuit, as shown in the figure given below. The wire AB is placed perpendicular to the plane of the paper. Place a magnetic compass near the wire and see the position of the needles. Pass the current through the circuit and observe the change in position of the needle. This change in position of the needle shows that, as the current passes through the wire magnetic effect is produced. more...

        Electrical Power   When electric current flows through the circuit it use up the electrical energy to do certain amount of work. The rate of doing work by the electric current is called the electrical power. It is given by   \[\text{Power }=\frac{\text{Electrical Work Done}}{\text{Time Taken}}\]                 Or,          \[P=\frac{W}{T}\] The SI unit of power is watt or joule per second. The power of one watt is defined as the rate of doing work of one joule per second. One kilowatt is equal to the 1000 watt. We can also define the electrical power as the rate of consuming electrical energy. Since we have, \[P=\frac{W}{T}\] But work done is equal to the \[B=V\times I\times T\] Therefore, \[P=\frac{V\times I\times T}{T}\] \[\Rightarrow \,\,P=V\times I\] Where V is potential difference and I is the current flowing through the conductor. But, \[V=I\times R\] Putting in the more...

         Domestic Circuit   The electric circuit which we use in our houses, is called the domestic circuit. In domestic circuit we normally use parallel connection, so that each appliance works independently and the fault at any point does not disrupt the working of other points. We use separate switches for each points and hence can operate independently. We have normally two types of circuit, i.e. parallel and series circuit. The main disadvantage of series circuit in the house hold is that, if one electrical point’s stops working due to some defects then all the other points will also stop working. Entire points works with one switch only and it is not possible to switch off any one point separately, at any instant. Apart from this all the points do not get same voltage of the power supply. The overall resistance of more...

       Combination of Resistance   There are two ways of connecting the resistance that is, the series combination and is parallel combination. Series Combination The combination, in which the resistance are connected end to end with each other, is called series combination.  Let \[{{R}_{1}},\,\,{{R}_{2}}\] and \[{{R}_{3}}\] be three resistance, connected in series across a battery of potential V volt, as shown in the figure above. Now suppose \[{{V}_{1}}\] be the potential difference across the resistance \[{{R}_{1}};\,\,{{V}_{2}}\] be the potential difference across \[{{R}_{2}};\] and \[{{V}_{3}}\] be the potential difference across \[{{R}_{3}}\]. The total potential across the three resistance is given by \[\mathbf{V=}{{\mathbf{V}}_{\mathbf{1}}}\mathbf{+}{{\mathbf{V}}_{\mathbf{2}}}\mathbf{+}{{\mathbf{V}}_{\mathbf{3}}}\] But by Ohms law, \[V=I\times R\] Since the same current I flows through the three resistance \[{{R}_{1}},\,\,{{R}_{2}}\]and \[{{R}_{3}}\], so by ohms law \[{{V}_{1}}=I\times {{R}_{1}},\,\,{{V}_{2}}=I\times {{R}_{2}}\]and\[{{V}_{3}}=I\times {{R}_{3}}\] Therefore, \[I\times R=I\times {{R}_{1}}+I\times {{R}_{2}}+I\times {{R}_{3}}\] \[\Rightarrow \,\,I\times R=I\times more...

       Electric Potential   What makes the charge flow through the conductors? Is it that the chargeflow on their own through the conductors? The answer to this question isno. The charge do not flow on their own through the conductors. The chargeflow through the conductors due to the difference of electric pressure which iscalled the potential difference. This difference of pressure may be generatedby a cell or a battery or any other sources. Thus, electric potential may bedefined as the amount of work done in taking a unit positive charge from infinityto a particular point. Therefore, \[V=\frac{W}{Q},\] Where, W is the work done Q is the total charge V is the potential difference   The SI unit of potential difference is volt and is named after Alessandro Volta and Italian Physicist. One volt is defined as the potential difference between two points in more...

       Introduction   One of the important sources of energy in modern time is the electricity. Modern life depends on electricity to a very large extent. All the modern development has been made possible due to the electricity. It is used everywhere, in house, in industry, transportation, and in what not?. Now the most important question is 'how is electricity produced?' and 'what is electricity'?          Electricity Atom consists of charge particles, such as, proton and electron. Protons are the positive charge particles and electrons are the negative charge particles, present in an atom. Electric current is generated by flow of charges through the conductors. It depends on the amount of charge flowing through the conductor, through a particular area and in a unit time. The rate of the flow of electric charge through the more...

     Human Eyes   It is one of the important-organ of human beings. It works on the’ refraction of light as the other optical instruments, like camera, telescope, microscope etc. In this part we discuss about the structure and various defects of human eyes. The main parts of human eyes are Cornea, iris, pupil, ciliary muscles, lens, retina, aqueous humour, vitreous humour, and optic nerves. Cornea is the outermost layer of the human eyes which is made up of a transparent substance and bulging outwards. The light enters into our eyes through cornea. In front of the eye, the choroid coat forms the iris. This may be pigmented and is responsible for the different color of the eye. An opening, the pupil, is present in the center of the iris. The size of this opening is variable and under automatic control. In dim light more...