Back(II) An ammeter whose internal resistance is 53 Ω reads 5.25 mA when connected in a circuit containing a battery and two resistors in series whose values are 760 Ω and 480 Ω. What is the actual current when the ammeter is absent?
(II) What is the internal resistance of a 12.0-V car battery whose terminal voltage drops to 8.2 V when the starter motor draws 95 A? What is the resistance of the starter?
A battery produces 40.8 V when 7.10 A is drawn from it, and 47.3 V when 2.80 A is drawn. What are the emf and internal resistance of the battery?
Electrocardiographs are often connected as shown in Fig. 26–78. The lead wires to the legs are said to be capacitively coupled. A time constant of 3.0 s is typical and allows rapid changes in potential to be recorded accurately. If C = 3.0μF, what value must R have? [Hint: Consider each leg as a separate circuit.]
Electronic devices often use an RC circuit to protect against power outages as shown in Fig. 26–84. (a) If the protector circuit is supposed to keep the supply voltage at least 75% of full voltage for as long as 0.20 s, how big a resistance R is needed? The capacitor is 7.6 μF. Assume the attached “electronics” draws negligible current. (b) Between which two terminals should the device be connected, a and b, b and c, or a and c?
Imagine that a steady current I flows in a straight cylindrical wire of radius R₀ and resistivity ρ.
(a) If the current is then changed at a rate dI/dt, show that a displacement current ID exists in the wire of magnitude ε₀ρ(dI/dt).
(b) If the current in a copper wire is changed at the rate of 1.0 A/ms, determine the magnitude of ID.
(c) Determine the magnitude of the magnetic field BD created by ID at the surface of a copper wire with R₀ = 1.00 mm. Compare (as a ratio) BD with the field created at the surface of the wire by a steady current of 1.0 A.
Draw a circuit diagram for the circuit of FIGURE EX28.1.
A capacitor is discharged through a 100 Ω resistor. The discharge current decreases to 25% of its initial value in 2.5 ms. What is the value of the capacitor?