Final answer:
The application of heat through an aquathermia pad on the back of a patient with arthritis can help relieve pain, reduce stiffness, and improve blood circulation in the affected area.
Step-by-step explanation:
When a nurse applies an aquathermia pad on the back of a patient with arthritis, the expected action that will occur is the application of heat. Heat therapy can help relieve pain, reduce stiffness, and improve blood circulation in the affected area. By increasing blood flow, heat can promote the healing process and provide temporary relief from arthritis symptoms.