1. a Physics Section, School of Distance Education, Universiti Sains Malaysia, 11800 Penang, Malaysia; ; chuahleesiang@usm.my, Email: chuahleesiang@yahoo.com
2. b School Of Physics, Universiti Sains Malaysia, 11800 Penang, Malaysia
3. c School Of Physics, Universiti Sains Malaysia, 11800 Penang, Malaysia