Question

a Here a colis connected to a resistor R The voltage output from the colis measured by data logger connected across the ends of the resistor Magnet printer computer data logger coil are processed to give a graphical printout of the results obtained when a bar magnet is dropped so that it falls freely through the colil cm per cm cm timebase 12 ms per cm Q1 Explain how the trace arises and why it looks like the figure Q2 Explain why the curve slopes upwards from A to B .Q3 Explain why the voltage shown at B has a smaller magnitude than the voltage shown at D Q4 Explain why the graph has a positive and a negative section

Answer 1

1. This trace arises because of the emf generated inside the coil due to the movement magnet. This follows laws of electromagnetic induction which say that whenever magnetic field lines associated with an inductor change an emf is induced into the coil.

2. The upward slope of the curve indicates an increase in the developing emf with respect to time and inward motion of the magnet inside the coil. As the magnet moves inward more and more magnetic field lines are associated with the coil are changing and thus increasing the value of induced emf.

3. This is a consequence of lenz law which states that direction of induced emf is such that it opposes the cause due to which it is produced thus leading to a lower value of peak in positive half as compared to negative half.

4. The positive half of the graph is due to the motion of the magnet through the coil which shows development of an emf upto a peak and then decareasing in magnitude once the magnet starts to exit the coil beyond B. Once the magnet passes through the coil this developed emf forms an RC circuit with the resistence R present in series with it. Which leads to the negative half of graph.