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Page 1 CURRENT ELECTRICITY  I 1. Electric Current 2. Conventional Current 3. Drift Velocity of electrons and current 4. Current Density 5. Ohm’s Law 6. Resistance, Resistivity, Conductance & Conductivity 7. Temperature dependence of resistance 8. Colour Codes for Carbon Resistors 9. Series and Parallel combination of resistors 10. EMF and Potential Difference of a cell 11. Internal Resistance of a cell 12. Series and Parallel combination of cells Page 2 CURRENT ELECTRICITY  I 1. Electric Current 2. Conventional Current 3. Drift Velocity of electrons and current 4. Current Density 5. Ohm’s Law 6. Resistance, Resistivity, Conductance & Conductivity 7. Temperature dependence of resistance 8. Colour Codes for Carbon Resistors 9. Series and Parallel combination of resistors 10. EMF and Potential Difference of a cell 11. Internal Resistance of a cell 12. Series and Parallel combination of cells Electric Current: The electric current is defined as the charge flowing through any section of the conductor in one second. I = q / t (if the rate of flow of charge is steady) I = dq / dt (if the rate of flow of charge varies with time) Different types of current: I t 0 a b c d) Alternating current whose magnitude varies continuously and direction changes periodically a) Steady current which does not vary with time b) & c) Varying current whose magnitude varies with time d Page 3 CURRENT ELECTRICITY  I 1. Electric Current 2. Conventional Current 3. Drift Velocity of electrons and current 4. Current Density 5. Ohm’s Law 6. Resistance, Resistivity, Conductance & Conductivity 7. Temperature dependence of resistance 8. Colour Codes for Carbon Resistors 9. Series and Parallel combination of resistors 10. EMF and Potential Difference of a cell 11. Internal Resistance of a cell 12. Series and Parallel combination of cells Electric Current: The electric current is defined as the charge flowing through any section of the conductor in one second. I = q / t (if the rate of flow of charge is steady) I = dq / dt (if the rate of flow of charge varies with time) Different types of current: I t 0 a b c d) Alternating current whose magnitude varies continuously and direction changes periodically a) Steady current which does not vary with time b) & c) Varying current whose magnitude varies with time d Conventional Current: Conventional current is the current whose direction is along the direction of the motion of positive charge under the action of electric field. + + + +     + + + +     I Drift Velocity and Current: Drift velocity is defined as the velocity with which the free electrons get drifted towards the positive terminal under the effect of the applied electric field. I v d =  (eE / m) t    v d E l A I = neA v d v d = a t v d  drift velocity, a – acceleration, t – relaxation time, E – electric field, e – electronic charge, m – mass of electron, n – number density of electrons, l – length of the conductor and A – Area of crosssection Current is directly proportional to drift velocity. Conventional current due to motion of electrons is in the direction opposite to that of motion of electrons. + + + I    Page 4 CURRENT ELECTRICITY  I 1. Electric Current 2. Conventional Current 3. Drift Velocity of electrons and current 4. Current Density 5. Ohm’s Law 6. Resistance, Resistivity, Conductance & Conductivity 7. Temperature dependence of resistance 8. Colour Codes for Carbon Resistors 9. Series and Parallel combination of resistors 10. EMF and Potential Difference of a cell 11. Internal Resistance of a cell 12. Series and Parallel combination of cells Electric Current: The electric current is defined as the charge flowing through any section of the conductor in one second. I = q / t (if the rate of flow of charge is steady) I = dq / dt (if the rate of flow of charge varies with time) Different types of current: I t 0 a b c d) Alternating current whose magnitude varies continuously and direction changes periodically a) Steady current which does not vary with time b) & c) Varying current whose magnitude varies with time d Conventional Current: Conventional current is the current whose direction is along the direction of the motion of positive charge under the action of electric field. + + + +     + + + +     I Drift Velocity and Current: Drift velocity is defined as the velocity with which the free electrons get drifted towards the positive terminal under the effect of the applied electric field. I v d =  (eE / m) t    v d E l A I = neA v d v d = a t v d  drift velocity, a – acceleration, t – relaxation time, E – electric field, e – electronic charge, m – mass of electron, n – number density of electrons, l – length of the conductor and A – Area of crosssection Current is directly proportional to drift velocity. Conventional current due to motion of electrons is in the direction opposite to that of motion of electrons. + + + I    Current density: Current density at a point, within a conductor, is the current through a unit area of the conductor, around that point, provided the area is perpendicular to the direction of flow of current at that point. J = I / A = nev d In vector form, I = J . A Ohm’s Law: The electric current flowing through a conductor is directly proportional to the potential difference across the two ends of the conductor when physical conditions such as temperature, mechanical strain, etc. remain the same. I V I a V or V a I or V = R I V I 0 Page 5 CURRENT ELECTRICITY  I 1. Electric Current 2. Conventional Current 3. Drift Velocity of electrons and current 4. Current Density 5. Ohm’s Law 6. Resistance, Resistivity, Conductance & Conductivity 7. Temperature dependence of resistance 8. Colour Codes for Carbon Resistors 9. Series and Parallel combination of resistors 10. EMF and Potential Difference of a cell 11. Internal Resistance of a cell 12. Series and Parallel combination of cells Electric Current: The electric current is defined as the charge flowing through any section of the conductor in one second. I = q / t (if the rate of flow of charge is steady) I = dq / dt (if the rate of flow of charge varies with time) Different types of current: I t 0 a b c d) Alternating current whose magnitude varies continuously and direction changes periodically a) Steady current which does not vary with time b) & c) Varying current whose magnitude varies with time d Conventional Current: Conventional current is the current whose direction is along the direction of the motion of positive charge under the action of electric field. + + + +     + + + +     I Drift Velocity and Current: Drift velocity is defined as the velocity with which the free electrons get drifted towards the positive terminal under the effect of the applied electric field. I v d =  (eE / m) t    v d E l A I = neA v d v d = a t v d  drift velocity, a – acceleration, t – relaxation time, E – electric field, e – electronic charge, m – mass of electron, n – number density of electrons, l – length of the conductor and A – Area of crosssection Current is directly proportional to drift velocity. Conventional current due to motion of electrons is in the direction opposite to that of motion of electrons. + + + I    Current density: Current density at a point, within a conductor, is the current through a unit area of the conductor, around that point, provided the area is perpendicular to the direction of flow of current at that point. J = I / A = nev d In vector form, I = J . A Ohm’s Law: The electric current flowing through a conductor is directly proportional to the potential difference across the two ends of the conductor when physical conditions such as temperature, mechanical strain, etc. remain the same. I V I a V or V a I or V = R I V I 0 Resistance: The resistance of conductor is the opposition offered by the conductor to the flow of electric current through it. R = V / I Resistance in terms of physical features of the conductor: I = neA  v d  I = neA (e E / m) t ne 2 At m V l I = ne 2 At V I = ml ne 2 t A R = m l A R = ? l where ? = ne 2 t m is resistivity or specific resistance Resistance is directly proportional to length and inversely proportional to crosssectional area of the conductor and depends on nature of material. Resistivity depends upon nature of material and not on the geometrical dimensions of the conductor.Read More
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1. What is current electricity? 
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