In an NMR spectrometer containing a 2.5 T magnet, Larmor precession frequency of 1 H is 100 MHz . The radiofrequency used in this spectrometer has an associated magnetic field strength of $2.5 \times 10^{-4} \mathrm{T}$. The duration of a $90^{\circ}$ pulse in this instrument is
(a)$25 \times 10^{-6} \mathrm{s}$
(b)$50 \times 10^{-6} \mathrm{s}$
(c)$25 \times 10^{-5} \mathrm{s}$
(d)$50 \times 10^{-5} \mathrm{s}$
Answer
Answer: A ✓ checked by 4AB · confidence high
Explanation
A 90° pulse needs γB₁t = π/2: t = π/(2 × 2.675×10⁸ × 2.5×10⁻⁴) = 2.3×10⁻⁵ s ≈ 25 μs.