Circuits

Drift speed When you connect a circuit, current flows IN EVERY PART of the circuit instantaneously (near the speed of light). ALL free electrons in the circuit start moving the moment the circuit is connected / the moment the electric field is applied. Batteries create potential difference, they do NOT supply electrons; the electrons come from the wire.

Drift speed When you connect a circuit, current flows IN EVERY PART of the circuit instantaneously (near the speed of light). ALL free electrons in the circuit start moving the moment the circuit is connected / the moment the electric field is applied. Batteries create potential difference, they do NOT supply electrons; the electrons come from the wire. Electrons move very fast (106 ms-1), but are not instantaneous.

Drift speed When you connect a circuit, current flows IN EVERY PART of the circuit instantaneously (near the speed of light). ALL free electrons in the circuit start moving the moment the circuit is connected / the moment the electric field is applied. Batteries create potential difference, they do NOT supply electrons; the electrons come from the wire. Electrons move very fast (106 ms-1), but are not instantaneous. Because electrons bounce around due to collisions with atoms in the wire, the average speed of electrons opposite the flow of current – known as drift speed – is VERY slow (0.01 cm/s)

Drift speed When you connect a circuit, current flows IN EVERY PART of the circuit instantaneously (near the speed of light). ALL free electrons in the circuit start moving the moment the circuit is connected / the moment the electric field is applied. Batteries create potential difference, they do NOT supply electrons; the electrons come from the wire. Electrons move very fast (106 ms-1), but are not instantaneous. Because electrons bounce around due to collisions with atoms in the wire, the average speed of electrons opposite the flow of current – known as drift speed – is VERY slow (0.01 cm/s) This means it can take an electron 3 hours to travel through 1 m of wire! it’s not even a snail’s pace!!!!!

Drift speed Turn & Talk with your table partner …The scholar with the bigger shoe size Define drift speed … The scholar with the smaller shoe size Respond to the following: “Lights turn on so quickly after you flip the switch because electrons move very quickly.”

Drift speed Turn & Talk with your table partner …The scholar with the bigger shoe size Define drift speed … The scholar with the smaller shoe size Respond to the following: “Lights turn on so quickly after you flip the switch because electrons move very quickly.”

Direct Current (DC) electric circuits a circuit containing a battery is a DC circuit in a DC circuit the current always flows in the same direction. Current flows from + to – Electrons flow the opposite direction Duracell +

Alternating Current (AC) Circuits AC movement of electrons in a wire _ + Power outlets supply AC current In an AC circuit the current reverses at a frequency of 50 Hz (US) or 60 Hz (Europe) !! the source of electrons are the free electrons in wire itself !! When you are shocked by AC current, the electrons that make the current come from your body. The current makes the electrons in your body vibrate.

How does the voltage and current change in time? In DC, current and voltage do not change direction over time the actual voltage in a 120-V AC circuit varies between +170V and -170V peaks. current time AC

Why do power plants produce AC? AC can be much more easily stepped up or down to different voltages through use of a transformer. Low voltage is good in a house because it is safer. High voltage is useful for transmitting current over large distances – thinner wires can be used and there is less loss to heat. This means that AC is cheaper to transmit and the plants can be farther from the users.

AC vs DC Turn and talk with your table partner … … the scholar who has a birthday earlier in the month Identify 3 differences between AC and DC … the scholar who has a birthday later in the month Describe two benefits of transmitting high voltage current

In the mid-nineteenth century, G. R In the mid-nineteenth century, G.R. Kirchoff (1824-1887) stated two simple rules using the laws of conservation of energy and charge to help in the analysis of direct current circuits. These rules are called Kirchoff’s rules.

Kirchoff’s rules 1. Junction rule – conservation of charge. ‘The sum of the currents flowing into a point in a circuit equals the sum of the currents flowing out at that point’. I1 + I2 = I3 + I4 + I5

Kirchoff’s rules 1. Junction rule – conservation of charge. ‘The sum of the currents flowing into a point in a circuit equals the sum of the currents flowing out at that point’. I1 + I2 = I3 + I4 + I5 This is a slight alteration to our ‘current is the same everywhere rule’ that we used before. It means that current can be split (or combined) at junctures.

Kirchoff’s rules V = V1 + V2 + V3 1. Junction rule – conservation of charge. ‘The sum of the currents flowing into a point in a circuit equals the sum of the currents flowing out at that point’. I1 + I2 = I3 + I4 + I5 2. Loop rule – conservation of energy principle ‘In a closed loop, the sum of the emfs equals the sum of the potential drops’. V = V1 + V2 + V3

Kirchoff’s rules V = V1 + V2 + V3 Emf = electromotive force = the potential difference supplied by a battery This is exactly the same as our rule that voltage is ‘used up’ across a circuit. 1. Junction rule – conservation of charge. ‘The sum of the currents flowing into a point in a circuit equals the sum of the currents flowing out at that point’. I1 + I2 = I3 + I4 + I5 2. Loop rule – conservation of energy principle ‘In a closed loop, the sum of the emfs equals the sum of the potential drops’. V = V1 + V2 + V3

Circuit Diagrams Common symbols ammeter – measures current voltmeter – measures current Branching points in the wire are called nodes

Circuit Diagrams You Do: Draw the schematic of the circuit

Exit Ticket True / False When a battery no longer works, it is out of charge and must be recharged before it can work again. The amount of charge that exits a light bulb is less than the amount that enters the light bulb. Draw the circuit schematic Batteries use ____________ current What is the major difference between AC and DC current? EC What is the major advantage for using AC current?