1. Electrifying! Ken McAuliffe Chapter 30

2. Summary Ken McAuliffe Explains the complexities of wiring a large building for electricity. Describes how electrical blackouts happen and explains how the Museum of Science is equipped with a battery and a back- up generator to provide uninterrupted power to the server room and the exhibit hall lights in the event of power loss. Explains the difference between AC and DC, and that current from the uninterrupted power source battery must be converted from DC to AC. Explains why many of the lights in the museum are wired in parallel instead of in series. Explores some important safety precautions that anyone working with electricity must take, involving circuit breakers, ground wires, and short circuits.

3. Alternating Current (AC) & Direct Current (DC) Alternating current, or AC, Is the type of current produced by power plants. It moves in one direction and then the opposite direction repeatedly. Many electrical appliances that plug into a wall socket use AC. Direct current, or DC, only flows in one direction. Batteries provide DC. Most electronic devices uses DC. AC often needs to be converted to DC, and vice versa.

4. A series and parallel circuits

5. Example 1 What is the total resistance across the voltage in the circuit below?

6. Example What is the total resistance across the voltage in the circuit below?

7. Example What is the total resistance across the voltage in the circuit below?

8. Safety precautions You should never work with circuits when water is present – water can create a short circuit. Whenever possible, disconnect the circuit from the power source when working on it. Use ground wire whenever possible.

9. Short circuit A short circuit is an accidental lower- resistance connection between two points on a circuit. A short circuit connects the hot wire to the ground wire, excluding the load from the circuit. In a short circuit, resistance drops and current can become dangerously high.

10. Question 1 Question In your own words, write a paragraph explaining how the museum’s electrical system would work if an electrical blackout happened? Answer When a blackout occurs, an Uninterrupted Power Source (UPS) system keeps the power up long enough for a generator to start functioning and provide power to essential systems.

11. Question 2 Question What is a short circuit? Why can short circuits be dangerous? Answer A short circuit is an accidental lower-resistance connection that bypasses the load, or the resistance in a circuit? This is dangerous because in a short circuit the current follows the path of least resistance, such as a metal bar, another conductor, or a person’s body. This causes resistance to drop and voltage to remain constant, which makes the current very strong. In wall current, a short circuit will occur when the hot wire is connected to the ground wire. Current and voltage are already high, so a short circuit can be very dangerous. Although the electrical energy in a battery is much less, accidentally connecting the positive and negative sides of a battery with a wire will drain the battery very quickly, and heat up the wire.

12. Question 3 Question Find the missing voltages, currents, and ohms

13. Answers! Answers Diagram A: 3 ohms and 2 amps Diagram B: 6 volts and 6 ohms Diagram C: 4 volts and 2 amps Diagram D: 2 volts and 2 volts Key points The voltage drop in the external circuit equals the voltage boost from the battery. Current is everywhere the same.