Question

You plan to conduct an experiment to see how magnetic field varies inside of a solenoid as a function of solenoid length. You will keep the current through the solenoid and the number of turns constant, but the number of turns per unit length will change (imagine a slinky stretched to different lengths). Write a valid hypothesis for this experiment in the if/then/because format, i.e. fill in the blanks: If (we perform this experiment) , then (we expect these results) , because (solid reasoning that is neither circular nor tautological) . Your score on this question will depend only on being able to create a scientifically valid hypothesis, not on whether your hypothesis would be supported or rejected once you performed the experiment.

Answer 1

If we increase the length of a solenoid keeping the current and total turns constant, then the magnetic field will become weaker, because now the same amount of current and turns have to create a magnetic field in a larger volume (the cyclindrical volume of the solenoid). Another way to justify it is by considering a point, say at the centre of the solenoid. If the length is small, the turns will be closer. Hence the magnetic field at that point will be influenced by a large number of turns. This is in contrast to an extended solenoid, in which turns being far away, lesser turns will be contributing to the magnetic field at the point considered. So, longer the length, weaker the magnetic field.