4) A scientist just bought a very cool magnet, and would like to measure it's strength. She takes a strip of copper with width 3.0cm, and a rectangular cross-section of 0.004m and runs a current of 0.5A through it. She knows copper has a free charge density of 8.491 1028 m3. She holds the magnet near the strip, and measures a voltage across the sides of the strips, and her voltmeter reads 11.2 nV- what is the strength of her magnet? (5 pt)