Electric Circuits

1. Electric Circuits • Electricity refers to the presence of electric current in wires, motors, light bulbs, and other devices. • Electric current is similar to a current of water, but electric current flows in solid metal wires so it is not visible. • Electric current can carry a lot of power.

2. 19.1 Electric Circuits • When drawing a circuit diagram, symbols are used to represent each part of the circuit. • These electrical symbols are quicker and easier to draw than realistic pictures of the components.

6. How does current move through a circuit? Current and Voltage

7. Current and voltage • Electric current is measured in units called amperes, or amps (A) for short. • One amp is a flow of a certain quantity of electricity in one second. • The amount of electric current entering a circuit always equals the amount exiting the circuit.

8. Current and voltage • Conventional current was proposed by Ben Franklin in the 1700’s. • Scientists later discovered that the particles that carry electricity in a wire actually travel from negative to positive. • Today, we still use Franklin’s definition.

9. Voltage • Voltage is a measure of electric potential energy, just like height is a measure of gravitational potential energy. • Voltage is measured in volts (V). • A voltage difference of 1 volt means 1 amp of current does 1 joule of work in 1 second.

10. Voltage • Since 1 joule per second is a watt (power), you can interpret voltage as measuring the available electrical power per amp of current that flows.

11. Voltage • The positive end of a 1.5 volt battery is 1.5 volts higher than the negative end. • If you connect batteries positive-to-negative, each battery adds 1.5 volts to the total. • Three batteries make 4.5 volts. • Each unit of current coming out of the positive end of the three-battery stack has 4.5 joules of energy.

12. 19.3 The ohm • Resistance is measured in ohms (W). • One ohm is the resistance when a voltage of 1 volt is applied with a current of 1 amp.

14. 19.3 Calculate current • A light bulb with a resistance of 2 ohms is connected in a circuit that has a single 1.5-volt battery. • Calculate the current that flows in the circuit. • Assume the wires have zero resistance.

15. 19.3 The resistance of electrical devices • The resistance of electrical devices ranges from very small (0.001 Ω) to very large (10×106 Ω). • Each device is designed with a resistance that allows the right amount of current to flow when connected to the voltage the device was designed for.

16. 19.3 Electrical Conductivity • The electrical conductivity describes a material’s ability to pass electric current.

17. 19.3 Conductors and insulators • A material such as copper is called a conductor because it can conduct, or carry, electric current. • Materials that insulate against (or block) the flow of current are classified as electrical insulators. • Some materials are neither conductors nor insulators. • These materials are named semiconductors.

18. 19.3 Resistors • Electrical components called resistors can be used to control current. • Resistors have striped color codes to record their "values" (writing on them is difficult).

19. 19.3 Potentiometers • Potentiometers are a type of "variable" resistor that can change from low to high. • They are wired so that as you turn the knob, it changes the distance the current has to flow.