The ionosphere is the ionized part of the upper layer of the earth's atmosphere. The air molecules there are ionized by solar radiation. This layer of the atmosphere is a fairly good conductor, and radio waves are often "bounced" off the bottom of the ionosphere back toward the earth, in a process called skip or skywave propagation. Due to these properties, the space between the surface of the earth and the bottom of the ionosphere acts like a closed wave guide that will exhibit resonance for very low frequencies. Resonance excitations in the cavity are caused by lightning strikes, which hit the earth about 50 to 100 times a second. These low atmospheric resonance frequencies are known as Schumann resonances, named after the physicist Winfried Otto Schumann, who first calculated them in 1952. There are several Schumann frequencies that occur in the low frequency background, which ranges from 3 to 60 Hz. The highest intensity resonance mode (called the fundamental) occurs at 7.83 Hz. Other Schumann resonances occur at 14.3, 20.8, 27.3, and 33.8 Hz. Around 20 years ago, research showed that the majority of biological systems exhibit electrical activity in the same range as the Schumann resonances. New theoretical work suggests that primordial cells synchronized their electrical activity to the natural atmospheric resonances, and this evolutionary process is evident today across a gigantic scale-from single-celled organisms to the electrical activity in our brains. The surface of the earth and the bottom of the ionosphere act like a giant capacitor, and we can model one path that stretches between them as a circuit consisting of a resistor and capacitor connected in series. Assume the atmosphere has an average resistance of 2.00 x 1022, and the capacitance is equal to 0.070 F. (a) What is the capacitive reactance of the circuit when it is active at the fundamental Schumann resonance frequency? (b) What is the impedance of this circuit? (c) What is the rms value of the current in the circuit, if the maximum voltage is 3.50 × 105 V? (a) Number (b) Number 0.29 2.00E2 (c) Number i 1238 Units Units Units Ω Ω A ◆ + A