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Defects of vision and correction

  WHAT HAPPENS WHEN CILIARY MUSCLES CANNOT ACCOMMODATE EYE LENS?   This happens when ciliary muscles become weak and cannot adjust the focal length of the eye lens. This may be due to ageing or some other reasons of lack of vitamins, etc When proper accommodation of eye lens is not done then it leads to defects of eye. We have mainly three defects of vision. They are:   1)     MYOPIA (SHORT SIGHTEDNESS): this defect is due to failure of adjusting maximum focal length of eye lens to 2.5 cm when seeing the far objects. The people with this defect have far point (M). And beyond far point the objects are not seen because f max for these people will be less than 2.5 cm. So image forms in front of retina. So these people can see a blur image of far objects (beyond M). So these people can see the objects only between least distance of distinct vision (L) and far point (M).   Far point: the extreme point from where an object appears clearly to a person with myopia is called f
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Series and parallel connection of resistors

  TYPES OF CONNECTIONS: Electric components can be connected in two ways SERIES:   When negative terminal of first component is connected to positive terminal of second component, negative terminal of second component is connected to positive terminal of third component and so on, then the components are said to be connected in series. PARALLEL:   when the positive terminals of all the components are connected to one end and the negative terminals of all the components are connected to another end, then the components are said to be connected in parallel. HOW TO FIND EQUIVALENT RESISTANCE OF COMBINATION OF RESISTORS CONNECTED IN SERIES AND PARALLEL? RESISTORS CONNECTED IN SERIES: In series connection of resistors there is only one path for the flow of current in the circuit. Hence, the current in the circuit is equal to i. But potential difference varies depending upon the resistance of a resistor. According to Ohm’s law, Potential difference across R 1 is , V 1 = iR 1 Potential dif
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Ohm's law, resistance and resistivity

 OHM’S LAW Before going to Ohm’s law let us discuss in brief about some electrical components or devices we use in electric circuits.    A Battery serves as a source of electricity in a circuit. We use mainly two measuring devices in this concept those are  Volt meter: used to measure potential difference between the two ends of a conductor. So it is always connected in parallel ( we learn about types of connections later in this chapter) Ammeter: used to measure the current passing in the circuit. So it is always connected in series. Now let us dive in to the activity did by Ohm to understand his concept. Materials required: 5 dry cells of 1.5V each, conducting wires, an ammeter, a volt meter, thin iron spoke of length 10cm, LED and key.   Procedure: Connect a circuit as shown in the above figure. Solder the conducting wires to the ends of the iron spoke. Close the key. Note the readings of current from ammeter and potential difference from volt meter in table     Now connect two cell
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