Physics of Magnetism PA STEM monthly meeting Lincoln HS, Philadelphia January 13, 2015

High-school standard HS-PS2-5 focuses on an inquiry-based study of the causes and effects of magnetism PA STEM Science HS-PS2-5: Plan and conduct an investigation to provide evidence that an electric current can produce a magnetic field and that a changing magnetic field can produce an electric current. [Assessment Boundary: Assessment is limited to designing and conducting investigations with provided materials and tools.]

Since magnetism is defined by its poles, it must be possible to identify the polarity of practical magnets Determine the polarity of an electromagnet Q: Does this depend on the direction of the current? Determine the poles of a compass needle Q: What does this imply about Earth’s poles? PA STEM Science

Ampere’s Law says that a current (moving charge) in a wire creates a circular magnetic field Follow the Right-Hand Rule II (RHR II): Place thumb of right hand along the current direction Fingers curl along direction of magnetic field around the wire PA STEM Science

Ampere’s Law can be used to determine the polarity of an electromagnet Determine the expected polarity of our electromagnet (Imagine a straight wire bent into a loop) PA STEM Science

Ampere’s Law can be used to determine the polarity of an electromagnet Determine the expected polarity of our electromagnet (Imagine a straight wire bent into a loop) PA STEM Science N

If Ampere’s Law shows how to make magnetism from flowing charge, what causes a permanent magnet? PA STEM Science

If Ampere’s Law shows how to make magnetism from flowing charge, what causes a permanent magnet? PA STEM Science Each atom acts as a tiny magnet from the motion of its orbiting electrons

A magnetic field exerts a force on moving charges PA STEM Science Try setting up a circuit to determine which way the force goes relative to the current.

A magnetic field exerts a force on moving charges PA STEM Science

Faraday’s Law says that a changing magnetic field can create a voltage in a wire with no battery PA STEM Science Use a coil and magnet setup to discover how the induced voltage depends on a changing magnetic field

The induced voltage depends on the number of turns of wire, the area of the coil, and the rate of change PA STEM Science V = voltage N = number of coils A = area of coils B = magnetic field  (BA) = change in flux  t = time interval

Faraday’s Law is the basis for electric generators and transformers PA STEM Science Schematic of transformer Schematic of electric generator