SP 212 Worksheet
Lesson 29: Ch. 30.7-30.8, Energy & Magnetic Fields
1) A 1300 turn solenoid is 1.2 m long and has a cross-sectional area of 18 cm2 . The solenoid carries a 9.0 A
current. a) Calculate the energy density of the magnetic field in the solenoid. b) Find the total energy stored
in the magnetic field.
2) What must be the magnitude of a uniform electric field if it is to have the same energy density as that
possessed by a 0.62 T magnetic field?
3) In the figure below, E = 12 V, R = 6.9 Ω, and L = 5.3 H. The battery is connected at time t = 0.
R
a) How much energy is supplied by the battery in the first 5.0 s? (E = P dt, where P = iE for a battery.)
b) At t = 5.0 s, how much energy is stored in the magnetic field of the inductor?
c) The battery is supplying all of the energy in the system. Energy can be stored in the inductor, and energy
can be dissipated by the resistor. So, the difference between your answers to a) and b) should be equal to
the energy dissipated by the resistor in 5.0R s. Explicitly calculate the energy dissipated by the resistor in the
first 5.0 s to show that this is true. (E = P dt, where P = i2 R for a resistor.)