Explanation:
\(\lambda = \frac{{(\mu - 1)t}}{n}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\left( 1 \right)\)
According to question
\(n = 7.\mu = 1.6,t = 7 \times {10^{ - 6}}\,\,\,\,\,\,\,\,\,\,\,\,\left( 2 \right)\) meter
From eqs. (1) and (2), \(\lambda = 6 \times {10^{ - 7}}\) meter
\(i.e.,\,\,\,6000\,\)\( \mathop A^{~~\circ} \)\(\quad \quad (1\,\) \( \mathop A^{~~\circ} \)\(\, = {10^{ - 10}}\,m\,)\)