Physics · Current Electricity · NEET
Use I = q/t only when the current is steady (constant), meaning equal charge crosses the area every second. When the charge changes with time in a non-linear way (like Q = at - bt^2), the current is not constant, so you must use the general formula I = dQ/dt. In NEET problems, if you are given Q as a function of time t, differentiate to get current.
1 ampere = 1 coulomb per second (1 A = 1 C/s). So if 2 coulomb of charge flows past a point in 4 seconds, the current is I = q/t = 2/4 = 0.5 A. The ampere is one of the seven SI base units, so charge (coulomb) is actually derived: 1 C = 1 A x 1 s.
Electric current is a scalar even though we talk about its direction along the wire. It does not add like a vector (using triangle law). At a junction, currents add algebraically following Kirchhoff's junction rule, not by vector addition. The direction only tells us the sense of flow, not a vector quantity. Current density J, however, IS a vector.
Charge (q, unit coulomb) is the amount of electricity that has flowed. Current (I, unit ampere) is how fast that charge flows, i.e. charge per second. Think of charge as the total water that passed and current as the flow rate (litres per second). Relation: q = I x t for steady current, or q = integral of I dt in general.
Reverse the formula. For steady current, q = I x t. For changing current, the charge is the area under the current-time (I vs t) graph, i.e. q = integral of I dt between the two times. This is a common NEET trick: given an I-t graph, total charge equals the area under it.
The charge through a resistance R varies with time as Q = at - bt^2 (a, b positive constants). The total heat produced in R is:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
For steady current, I = q / t (charge divided by time). For current that changes with time, the general formula is I = dQ/dt, the rate of flow of charge.
The SI unit of electric current is the ampere (A). It is one of the seven SI base units. 1 ampere = 1 coulomb per second (1 A = 1 C/s).
1 ampere means 1 coulomb of charge crosses a cross-section of the conductor every second. In symbols, 1 A = 1 C / 1 s.
Electric current is a scalar quantity. It has a direction of flow but adds algebraically (Kirchhoff's junction rule), not by vector laws.
Charge equals current times time for steady current: q = I x t. For changing current, charge equals the area under the current-time graph, q = integral of I dt.
