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在磁场和电磁感应习题中,常遇到线圈是单匝还是N匝(多匝)的题设条件。到底什么情况下选用N,什么情况下不要选用N,下面总结这方面的选用规律。 1.不选用匝数N 凡是直接应用公式求磁通量(φ=BScosθ)、磁通量的变化量(Δφ=φ_2-φ_1=·ΔScosθ-S·ΔBcosθ)、磁通量的变化率(Δφ/Δt),匝数N不必选用。因为磁通量表示穿过某一面积的磁力线条数,由公式φ=BScosθ可知,即使线圈的匝数很多,但线圈所围面积S不变。反之亦然。表明磁通量大小不受线圈匝数N的多少影响。同理,Δφ、Δφ/Δt的大小也不受线圈匝数N的影响。
In the magnetic field and electromagnetic induction exercises, it is often encountered whether the coil is a single-turn or N-type (multiple turns) problem. In the end, when N is selected, under what circumstances do not use N. The following summarizes the selection rules in this area. 1. Do not select the number of turns N. Apply directly the formula to find the magnetic flux (φ=BScosθ), the amount of magnetic flux change (Δφ=φ_2-φ_1=·ΔScosθ-S·ΔBcosθ), the change rate of the magnetic flux (Δφ/Δt), and number of turns N does not have to choose. Since the magnetic flux represents the number of magnetic lines passing through a certain area, the equation φ = BScos θ shows that even if the number of turns of the coil is large, the area S surrounded by the coil does not change. vice versa. It shows that the magnetic flux is not affected by the number of turns of the coil N. Similarly, the magnitudes of Δφ and Δφ/Δt are not affected by the number of turns of the coil N.