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Q1. An electron beam has an aperture of 2 mm². A total of 7 × 10¹⁵ electrons flow through any perpendicular cross-section per second. Calculate the current density of the electron beam. Q2. The charge in a given wire varies with time, given by -     q = 3t³ - t² Where, q in 'C' and t in 'secs'. Find the current flowing in the wire at 4th second. Q3. The current flowing in a conductor is the function of time, given by -    I = 8t - 3 Where, I in 'Ampere' and t in'secs'. Find the total charge flowed in first 5 seconds in the conductor. Also, find the charge which flowed from 6th to 8th second. ----------------------------------------------------------------------             ANSWERS A1. 560 Am-² A2. 136 A A3. 85 C, 106 C Introduction to CURRENT ELECTRICITY (Basic Concepts) CLICK HERE by  www.advguruji.blogspot.com

Electric Current It is defined as the rate of flow of positive charge. It has the direction towards the motion of positive charge and direction opposite to the motion of negative charge. It is denoted by I. Its SI unit is ampere(A) or C/s. It is of two types :- Direct current [DC] Alternating current [AC] Direct Current ( DC) The current which has a same direction of flow. It is of two types : 1. fluctuating current The current whose magnitude changes again and again is called fluctuating current. 2. Steady current or ideal current The current whose magnitude do not changes with time is called steady current. Alternating current (AC) The current which changes its direction of flow periodically. (In detail, chapter 7) On the basis of calculation Current is of two types : 1. Average current [ I = q/t ] It is defined as the ratio of total charge flow to the total time of flow. 2. Instantaneous current [ I = dq/dt ] It is defined as the ratio of small change in c