William Charles Hansen, 75, who was a physicist before turning to a career in law, died June 25 of cardiopulmonary arrest at Washington Adventist Hospital. He lived in Silver Spring.

He began his career with the National Bureau of Standards while an undergraduate at the University of Maryland, from which he received a bachelor's degree in physics in 1950. He was a member of the Phi Sigma Kappa fraternity.

He received a master's degree in physics from George Washington University, where he also taught. He was a physicist with the National Bureau of Standards and Texas Instruments until the late 1960s, when he went to law school.

After graduating from the Washington College of Law at American University in 1972, Mr. Hansen organized the firm of Hansen, Smallwood & Kettlestrings in Silver Spring and practiced corporate and criminal law. He later opened a solo practice in Silver Spring, specializing in real estate, corporate and estate law and maintained his practice until his death.

He was born in Brooklyn, N.Y., and moved to Washington in 1941. As a youth, he was a member of the boys choir of St. John's Episcopal Church and sang for President Franklin D. Roosevelt. He graduated from Coolidge High School in 1946.

He was a longtime member of Trinity Episcopal Church in the District. He was also a member of the Rotary Club of Silver Spring and the Masons.

A skilled musician, Mr. Hansen played the clarinet and banjo throughout his life. He was also a photographer, stamp collector and talented cook.

He was well read on many subjects and introduced his children to the novels of Gabriel Garcia Marquez and Guy de Maupassant. He raised orchids at his home in Silver Spring.

His marriages to Joan Hansen and Gerri Hansen ended in divorce.

Survivors include six children from his first marriage, Karen Hansen of Wilmington, Del., Judith Hansen of Chevy Chase, Susan Evans of Fairfax County, Charles Hansen of Silver Spring and John Hansen and Christine Martin, both of Washington; and 12 grandchildren.