Electricity Notes Part-1 PDF

ELECTRICITY Electric Charges (Q) Electric charges are of two types: (+)positive charges & (-)negative charges Properties of electric charges: The total charge of an isolated body always remains the same or constant Like charges repel while unlike charges attrac...

ELECTRICITY Electric Charges (Q) Electric charges are of two types: (+)positive charges & (-)negative charges Properties of electric charges: The total charge of an isolated body always remains the same or constant Like charges repel while unlike charges attract each other. Charges can neither be created nor be destroyed but can be transformed from one body to another. This is called the law of conservation of charges Charge of an electron= -1.6x𝟏𝟎−𝟏𝟗C Charge of a proton=1.6x𝟏𝟎−𝟏𝟗C The SI unit of electric charge is coulomb(C) Define 1 coulomb(C) 1 coulomb is equivalent to the total charge contained in nearly 6x𝟏𝟎𝟏𝟖 electrons. Q: Calculate the number of electrons that constitute 1coulomb of charge. Charge of 1 electron (e) =1.6x𝟏𝟎-19 C Total charge(Q)=1C Number of electrons=? Q=ne n= 𝑸/ 𝒆 = 𝟏𝑪 /1.6x𝟏𝟎−𝟏𝟗𝑪 =0.625x𝟏𝟎𝟏𝟗= 6.25x𝟏𝟎𝟏𝟖=6x𝟏𝟎𝟏8 Calculate the number of electrons that constitute 4 coulomb of charge. n= 𝟒𝑪 /1.6x𝟏𝟎−𝟏𝟗𝑪 =2.5x𝟏𝟎𝟏𝟗=25x𝟏𝟎𝟏8 ELECTRIC CIRCUIT A continuous and closed path of an electric current is called an electric circuit. There are two types of circuit, open circuit and closed circuit. ELECTRIC CURRENT (I) Electric current is expressed by the amount of electric charge flowing through a particular area in unit time. It is the rate of flow of charge in a circuit. If Q is the charge flowing through the cross section of a conductor in time t 𝑐ℎ𝑎𝑟𝑔𝑒 Electric current= 𝑡𝑖𝑚𝑒 𝑄 I= 𝑡 Note: The conventional direction of electric current is from the positive terminal (higher potential) of the source of electric current (cell or battery) to its negative terminal (lower potential). Unit of current The S I unit of electric current is ampere, and is denoted by the letter ‘A’, named after the French scientist Andre-Marie Ampere.  Define 1 ampere When one coulomb of charge flows through a conductor in 1 second, then the current flowing through it is said to be 1 ampere. 𝟏𝑪 1A= 𝟏𝑺 Smaller units of current are , milliampere ( 1mA) =𝟏𝟎−𝟑A microampere(1µA)=𝟏𝟎−𝟔A. An electric current is a scalar quantity. An instrument called ammeter is used to measure the electric current in a circuit. Ammeter is always connected in series in an electric circuit through which current is to be measured because it is a low resistance device. A schematic diagram of an electric circuit comprising -cell, electric bulb, ammeter and plug key Numericals 3) A charge of 5 C flows through any cross section of a conductor in 10 seconds. What is the current flowing through the conductor? Q=5C t=10s I=? We have, I =𝑸/ t I= 5𝐶/ 10𝑠 =0.5A 4) A current of 0.2 A is drawn by the filament of an electric bulb for 30minutes. Find the amount of electric charge that flows through the circuit? I=0.2A t=30minutes=30x60=1800s Q-? we have, I =𝑸/t Q=It =0.2x1800 =360C ELECTRIC POTENTIAL AND POTENTIAL DIFFERENCE [V] The electric potential difference between two points in an electric circuit is defined as the amount of work done to move a unit charge from one point to other.  𝑤𝑜𝑟𝑘 𝑑𝑜𝑛𝑒 Potential difference (V) between two points = 𝑐ℎ𝑎𝑟𝑔𝑒 𝑾 Electric potential, V = 𝑸 Unit of electric potential The SI unit of electric potential difference is volt denoted as V, named after Alessandro Volta. Define 1 Volt(V) One Volt is the potential difference between two points in a current carrying conductor when 1 joule of work is done to move a charge of 1 coulomb from one point to other. 𝟏𝑱 1V= 𝟏𝑪 The potential difference is measured by means of an instrument called the voltmeter. The voltmeter is always connected in parallel across the points between which the potential difference is to be measured. NUMERICALS 1)How much work is done in moving a charge of 3 C across two points having a potential difference of 15 V? Q=3C V=15V W=? We have, V = 𝑾 /𝑸 Then, W=VQ= 15X3 = 45J 2) 80 J of work is done in moving a charge of 4 C from one terminal of a battery to another. What is the potential difference of the battery? W=80J Q=4C V=? We have, V = 𝑾 /𝑸 V= 𝟖𝟎 /𝟒 = 𝟐𝟎V COMMON SYMBOLS USED IN CIRCUIT