PHYS208 Fundamentals of Physics II

November 15, 1993    Midterm Exam 2

1. a.

• If a charged particle moves undeflected through some region of space, the magnetic field must be zero in that region.

No deflection means only that the resultant force is zero; the magnetic force may be balanced by an electric force with crossed E and B fields.

• If a charged particle is deflected sideways when moving through a region of space, we can be sure that a magnetic field exists in that region.

It could be the case that only an E field is in the region.

• The direction of an induced emf is always opposite to the magnetic field that induced it.

The induced emf opposes the change in B flux; in the presence of a decreasing field with fixed area, the current will be induced so that the B field it would create would be in the same direction as the inducing field.

1. b.  In which direction will the electron circulate?

clockwise

1. c.  What circuit element would convert it into an ammeter that reads 3.0 mA full scale?

3.6 ohm resistor in parallel

2.

 capacitive branch inductive branch power supply initial current (mA) 100 0 100 final current (mA) 0 500 500 time constant (microsec) 100 50 n/a current (mA) after 50 microsec 60 320 380

3. b.  Given a solenoid of length 50 cm, diameter 10 cm, 250 turns, which carries a current of 5.0 A, evaluate the magnetic field.

3.14 mT

3. c.  If the current drops steadily to zero in 10 ms, what emf is induced in a single-turn loop (diameter 50 cm) outside the solenoid?

2.5 mV

4. c.  Now estimate the inductance per unit length.

0.64 mu0

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Last updated Nov. 9, 1997.
Copyright George Watson, Univ. of Delaware, 1997.