Final answer:
The two metal posts on a battery are its terminals; one is positive, the other is negative, and their role is to create a secure connection for electrical devices by facilitating an electric current in a circuit. In a car, connecting one battery terminal to the metal body allows it to act as part of the circuit, reducing the need for additional wiring.
Step-by-step explanation:
The battery can be connected to a bell to produce sound. The question about why there are two metal posts on the battery is related to their function in a circuit. The correct statement that explains the existence of these two metal posts is: C. The metal posts create a secure connection for electrical devices. These posts are the battery's terminals, one marked as positive and the other as negative. When a battery is included in a circuit design, it provides the necessary electrical energy by driving an electric current from the negative terminal through the circuit and re-entering the battery through the positive terminal. The flow of electrons from the negative to the positive terminal facilitates this process. In a car, for instance, connecting one terminal to the metal body allows the body itself to act as a conductor, eliminating the need for a second wire for current to return to the battery, thus completing the circuit with only a single wire connected to the electrical devices.
Additionally, when a wire is placed directly across the two terminals of a battery, shorting out the terminals, the battery gets hot because of the low resistance path created for the electric current, causing a large flow of electrons which results in the generation of heat. Lastly, the law of conservation of charge states that the number of electrons leaving the negative terminal will be equal to the number entering the positive terminal in a closed circuit.