A tightly wound long solenoid carries a current of  $$1.5\,A.$$ An electron is executing uniform circular motion inside the solenoid with a time period of  $$75\,ns.$$ The number of turns per metre in the solenoid is $$\underline{\hspace{1cm}}.$$ [Take mass of electron  $$m_e=9\times10^{-31}\,kg,$$  change of electron $$|q_e|=1.6\times10^{-19}\,$$ $$C,$$ $$\mu_0=4\pi\times10^{-7}\,N$$ $$A^{-2},\,1\,ns=10^{-9}\,s]$$