INTERSTATE POWER AND LIGHT COMPANY (an Iowa corporation) 5.50% SENIOR DEBENTURES DUE 2025 PURCHASE AGREEMENT Dated: July 18, 2005Interstate Power and Light Company • July 19th, 2005 • Interstate Power & Light Co • Electric & other services combined • New York
Interstate Power and Light Company, an Iowa corporation (the “Company”), confirms its agreement with Barclays Capital Inc. (“Barclays Capital”), Banc of America Securities LLC (“Banc of America”) and each of the other underwriters named in Schedule A hereto (collectively, the “Underwriters”, which term shall also include any underwriter substituted as hereinafter provided in Section 10 hereof), for whom Barclays Capital and Banc of America are acting as representatives (in such capacity, the “Representatives”), with respect to the issue and sale by the Company and the purchase by the Underwriters, acting severally and not jointly, of the respective principal amounts set forth on Schedule A of $50,000,000 aggregate principal amount of the Company’s 5.50% Senior Debentures due 2025 (the “Securities”). The Securities will be issued pursuant to an indenture dated as of August 20, 2003 (the “Indenture”) between the Company and J.P. Morgan Trust Company, National Association, as successor in
