Transcript1a //Ashley is reading from a book

Ashley: "A linear dielectric sphere is located above a conducting surface in vacuum. A uniform surface charge is present on the sphere. Calculate the scalar potential for this system. Find a non-retarded solution."

1b

Mike: "Wait, what was that last sentence?"

Ashley: "Find a non-retarded solution."

2

Mike: "Isn't that a bit offensive to intellectually-disabled people?

Ashley: "What? All it's saying is to find a solution that doesn't consider the propagation time of electromagnetic fields..."

Ashley: "Eh, never mind. Go ahead and find a retarded solution."

3 //Mike is giving an exam to his students

Mike: "Here's your exam. You have 45 minutes to complete it."

Student: "Uh, is the last part of Question 1 right?"

Mike: "Yes, it is."

4 //Looking at exam paper

Question 1: A train leaves Oklahoma City, travelling southbound at 40 miles per hour. At the same time, another train leaves Fort Worth, 200 miles away, travelling northbound at 50 miles per hour. How much time elapses before the NTSB is called to investigate the headon collision in Ardmore? Find a non-retarded solution.

Question 2: Suppose a hole is drilled straight through the earth between the U.S. and Australia. An object is dropped into the hole. How long does it take for the object to come out the other side of the hole, assuming no air resistance? Is the time different if the hole is instead drilled to Russia? Find a non-retarded solution.

Mike: "You can neglect relativistic effects in these problems."