Pamela produced an electromagnet by wrapping a copper wire around an iron nail. When she connected the wire ends to a battery, she was able to lift four paper clips with her electromagnet. She decided that she wanted to modify the electromagnet so that it would lift seven paper clips. She modified the electromagnet by removing the iron nail and replacing it with an aluminum nail. However, when she modified the electromagnet, it would not lift any paper clips.

Explain how Pamela could modify the electromagnet so that it will lift seven paper clips.