D Learning Goal: O To understand the concept of electromotive force and internal resistance; to understand the processes in one-loop circuits; to become familiar with the use of the ammeter and D voltmeter. In order for the current in a conductor to exist continuously, the conductor must be part of a loop, that is, a closed path through which the charged particles can move without Submit Previous Answers creating a "build-up." Such build-up, if it occurs, creates its own electric field that cancels out the external electric field, ultim the current to stop. V Correct However, having a loop, or a closed circu s not enough to maintain the current; there must also be a source of energy. Its In diagram A, the voltmeter is connected in series with the battery. Since the voltmeter has a very large resistance there is no (or nearly zero) current in the whole circuit. Therefore, the ammeter reads sity is fairly obvious: As charged particles no current. In diagram B, the current through the ammeter is the same as the current through the voltmeter. Since the resistance of the voltmeter is very large, the current is nearly zero. move along the circuit, they lose potential energy. In fact, electrostatic forces always push the particles in the direction that leads to a decrease in potential energy. At some point, each charged particle would reach the location in the circuit where it has the lowest possible potential energy. How can such a particle move toward a point where it would have a higher potential energy? The last group of questions refers to a battery that has emf 12.0 volts and internal resistance 3.00 ohms. Such a move requires that nonelectrostatic forces act upon the charged particle, pushing it toward higher potential e spite the presence of electrostatic forces. In circuits, such forces exist inside a device commonly known as a battery. In a circuit, the Part H battery serves as the energy source that keeps the charged particles in continuous motion by increasing their potential energy through the action of some kind of nonelectrostatic force. A voltmeter is connected to the terminals of the battery; the battery is not connected to any other external circuit elements. What is the reading of the voltmeter The amount of work that the battery does on each coulomb of charge that it "pushes Express your answer in volts. Use three significant figures. through" is called (inappropriately) the electromotive force (pronounced "ee-em-ef" and abbreviated emf or denoted by &). Batteries are often referred to as sources of emf AV = 12.0 V (rather than sources of energy, even thou fundamentally, sources of energy). The emf of a battery can be calculated using the definition mentioned above: E = W/q. The units of emf are joule Submit per coulomb, that is, volts. Previous Answers The terminals of a battery are often labe + and - for "higher potential" and "lower potential," respectively. The potential difference between the terminals is called the Correct terminal voltage of the battery. If no current is running through a battery, the terminal voltage is equal to the emf of the battery: A Vbat = However, if there is a current in the circuit, the terminal voltage is less than the emf Part I because the battery has its own internal resistance (usually labeled r). When charge q passes through the battery, the battery does the amount of work &q on the charge; however, the charge also "loses" the amount of energy equal to Ir ( I is the current through the circuit); therefore, the increase in potential energy is Eq - qIr, and the The voltmeter is now removed and a 21.0-ohm resistor is connected to the terminals of the battery. What is the current I through the battery? terminal voltage is Express your answer in amperes. Use two significant figures. AVbat = E - IT. I = 0.50 A In order to answer the questions that follow, you should first review the meaning of the symbols describing various elements of the circuit, including the ammeter and the Submit Previous Answers voltmeter; you should also know the way the ammeter and the voltmeter must be connected to the rest of the circuit in order to function properly. Note that the internal resistance is usually indicated as a separate resistor drawn next to Correct the "battery" symbol. It is important to keep in mind that this resistor with resistance r is actually inside the battery. In all diagrams, & stands for emf, r for the internal resistance of the battery, and R for Part J the resistance of the external circuit. As usual, we'll assume that the connecting wires have negligible resistance. We will also assume that both the ammeter and the voltmeter are ideal: That is, the ammeter has negligible resistance, and the voltmeter has a very large resistance. In the situation described in Part I, what is the current I through the 21.0-ohm resistor? Express your answer in amperes. Use two significant figures. Figure Submit Request