Physics · Electromagnetic Induction · NEET
Because the wire is wound N times, and the same magnetic flux Φ passes through each single turn. Faraday's law for one loop gives EMF = -dΦ/dt. Since all N turns are connected end-to-end (in series), their EMFs add up. So total EMF = -N dΦ/dt. Here Φ is the flux through ONE turn, and N accounts for how many identical turns are stacked. NCERT states it plainly: for a closely wound coil of N turns, the change of flux linked with each turn is the same, so the total EMF is N times the single-turn EMF.
Φ is the flux through ONE single turn. The full-coil quantity is called flux linkage and equals NΦ. That is why the formula -d(NΦ)/dt = -N dΦ/dt appears. Students who plug the total coil flux AND multiply by N double-count. Rule: use flux through one turn, then multiply by N once.
In the EMF formula EMF = -N dΦ/dt, N is the TOTAL number of turns (a plain count, no units). The symbol n (small n) usually means turns per unit length (turns per metre), which appears in solenoid formulas like B = μ₀nI. Do not mix them. Capital N = total turns; small n = turns per metre. Reading N as turns-per-metre in an EMF problem is a common NEET slip.
In a closely wound (tightly packed) coil, every turn sits in almost the same place, so the same magnetic field lines thread through each of them. Same B and same area means same flux Φ, and they all change at the same rate dΦ/dt. Equal rate of change gives equal EMF per turn, so we can simply multiply one turn's EMF by N.
EMF (the source push) and resistance are separate things. Adding turns adds N EMFs in series, which raises the total driving EMF. The turns also add wire, which raises resistance, but EMF is defined before any current flows. In Faraday's law EMF = -N dΦ/dt, resistance never appears; it only matters later when you use I = EMF/R to find current.
A 800 turn coil of effective area 0.05 m² is kept perpendicular to a magnetic field 5 × 10⁻⁵ T. When the plane of the coil is rotated by 90° about a coplanar axis in 0.1 s, the emf induced in the coil will be:
An emf is generated by an ac generator having a 100 turn coil of loop area 1 m². The coil rotates at one revolution per second in a uniform magnetic field of 0.05 T perpendicular to the axis of rotation. The maximum value of emf is:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
EMF = -N dΦ/dt, where N is the total number of turns and Φ is the magnetic flux through a single turn. The minus sign is Lenz's law (direction); the size is N times the rate of change of flux.
Flux linkage is NΦ, the total flux 'seen' by the whole coil. Faraday's law can be written EMF = -d(NΦ)/dt. Since N is constant, this becomes -N dΦ/dt.
Yes, for the same flux change. Doubling the turns doubles the EMF because you stack twice as many equal EMFs in series. This is why real coils and generators use many turns.
When you deal with a single loop or a single moving rod (motional EMF ε = Bvl), N = 1, so no separate N is written. N only appears for multi-turn coils.
No. N is a pure count of turns, so it has no units. This makes checking units easy: the units of EMF come entirely from dΦ/dt (weber per second = volt).
