Lesson 1: Electric Current - objectives

1. Lesson 1: Electric Current - objectives • What is an Electric Circuit? • Requirements of a Circuit • Electric Current • Power: Putting Charges to Work • CommonMisconceptions Regarding Electric Circuits

2. lab: light a light bulb • Objective: light a light bulb • Material: one battery, one wire, one light bulb. • Record all different ways your connection did not work. • Record all different ways your connection did work. • Write your conclusion – what you must do in order for the light bulb to work.

3. + Light Bulb Anatomy • A light bulb is a device consisting of a filament attached to two wires. The wires and the filament are conducting materials which allow charge to flow through them. One wire is connected to the ribbed sides of the light bulbs. The other wire is connected to the bottom base of the light bulb. The ribbed edge and the bottom base are separated by an insulating material which prevents the direct flow of charge between the bottom base and the ribbed edge. The only pathway by which charge can make it from the ribbed edge to the bottom base or vice versa is the pathway which includes the wires and the filament.

4. What is an Electric Circuit? A circuit is simply a closed loop through which charges can continuously move. • The Requirement of a circuit • There must be a closed conducting loop in the external circuit which stretches from the high potential, positive terminal to the low potential, negative terminal. • There must be an energy supply capable doing work on charge to move it from a low energy location to a high energy location and thus establish an electric potential difference across the two ends of the external circuit.

5. Electric Current • If the two requirements of an electric circuit are met, then charge will flow through the external circuit. This flow of charge or current, is the rate at which charge flows past a point on a circuit. Current is arate quantity. Like velocity - the rate at which an object changes its position. Acceleration - the rate at which an object changes its velocity. And power - the rate at which work is done on an object. In every case of a rate quantity, the mathematical equation involves some quantity over time.

6. Electricity Comes Alive 4.2.1 Electrical Current

7. Definitions • current: RATE OF CHARGE FLOW • unit: C/s or AMPERE • requires: • POTENTIAL DIFFERENCE • PATH FOR FLOW

8. Example #1 • 100 coulombs of charge pass through point A in 4.0 seconds. • What is the rate of current flow through point A? I = Δq / t I = 100 C / (4.00 s) I = 25 A A

9. Example #2 • During a thunderstorm a lightning strike transfers 15.0 coulombs of charge in 10.0 milliseconds. • What was the electrical current produced in the strike? I = Δq / t I = 15.0 C / (10 x 10-3 s) I = 1.5 x 105 A

10. Example #3 • A wire carries a current of 50 amperes. • How much charge flows through the wire in 10 seconds? • How many electrons pass through the wire in 10 seconds? I = Δq / t 50 A = q / (10 s) q = 500 C 3.125 x 1021 e

11. example • If charge flowing at the rate of 2.50 × 1016 elementary charges per second. What is the electric current?

12. Conventional Current Direction The direction of an electric current is by convention the direction in which a positive chargewould move.

13. Current versus Drift Speed Current has to do with the number of coulombs of charge that pass a point in the circuit per unit of time. • Drift speed refers to the average distance traveled by a charge carrier per unit of time. Even though the drift speed is extremely slow, the current could be big. This is because there are many, many charge carriers moving at once throughout the whole length of the circuit.

14. The Nature of Charge Flow • We know that the average drift speed of an electron is very, very slow, why does the light in a room or in a flashlight light immediately after the switched is turned on? • Charge carriers in the wires of electric circuits are electrons. They are already there supplied by the atoms of the wire. Once the switch is turned to on, there is an electric potential difference established across the two ends of the external circuit. The electrons begin moving along a zigzag path in their usual direction. Thus, the flipping of the switch causes an immediate response throughout every part of the circuit, setting charge carriers everywhere in motion in the same net direction. • While the actual motion of charge carriers occurs with a slow speed, the signal that informs them to start moving travels at a fraction of the speed of light.

15. The charge carriers never become consumed or used up. While the energy possessed by the charge may be used up, the charge carriers themselves do not disintegrate, disappear or otherwise become removed from the circuit. And there is no place in the circuit where charge carriers begin to pile up or accumulate. The rate at which charge enters the external circuit on one end is the same as the rate at which charge exits the external circuit on the other end.

16. End of 4.2.1 - PRACTICE

17. Know: • Definition and equation for electrical current. Understand • When given a path, charged objects flow from areas of high electrical potential to areas of low electrical potential. Be able to • Determine the rate of current; number of charges; or time in system in which charge is flowing from one point to another. • Convert from charge in coulombs to elementary charge to determine the number of electrons flowing through a system.