Electric Current

•When electric charges (electrons) move from one place to another, they are known as an electric current

•Current is defined as the amount of charge passing a point in a given time

Current=

Flow of Electrons

Calculating Current

I = Q ∆t

•I – current (Amperes A or C/s)

•Q – total charge (C)•∆t – time (s)

Current Video

https://www.youtube.com/watch?v=8gvJzrjwjds

Direction of Current

•Convention says current moves from the positive terminal of a battery to the negative terminal

•In actual circuits, electrons move from the negative terminal to the positive terminal

•We stick with convention so we get a positive current value

Measuring Current

•We measure current using an ammeter that must be placed in series with (in the path of) the current

•Current is measured in amperes (A)

Sample Problem

•If 8.44 x 109 electrons pass a point in 10 s, what is the current produced by this flow of charges?

•Ans: 1.35 x10-10A

SolutionN = 8.44 x 109 electrons∆t = 10 s

Q = Ne = (8.44 x 109)(1.60x10-19) = 13.5 x 10-10 C  I = Q = 13.5 x 10-10 = 1.35 x 10-

10A ∆t 10

Electric Potential Difference

What is EPD?•Electric Potential (V) – the amount of work required per unit charge to move a positive charge from one point to another in an electric field

•Since work is energy, think of EPD as the amount of energy given to an electron due to an electric field

•We usually refer to EPD as Voltage which is from the unit for Electric Potential Difference – the VOLT

Voltage=

Energy

Voltage Videoshttps://www.youtube.com/watch?v=F1p3fgbDnkY

Measuring Voltage

•Measured using a voltmeter that is placed in parallel

Calculating EPD

V = W Q

•V – Electric Potential Difference (V)

•W – Work required to move a charge from one point to another in an electric field (J)

•Q – amount of charge moved (C)

•As charged electrons pass through a circuit they lose energy as work is done (ie. Travelling through a light bulb)

∆E = V I ∆t

•V – Electric Potential (V)•I – Current (A)•∆t – time (s)

Sample Problem

•How much energy is used by a light bulb, that has a current of 1.0A and an electric potential of 120V, that is left on for 3 minutes?

•Ans: 21.6 kJ

Solution

•I = 1.0A V = 120V•∆t = 3 hr = 3*60 = 180s•∆E = ?

∆E = V I ∆t∆E = (120V)(1.0A)(180s)∆E = 21600 J∆E = 21.6 kJ

Homework1) If 4.5 x 1025 electrons pass a point in 0.82s what current is flowing

in the circuit?2) If 6 A of current passes through a light, how many electrons will

pass through in 1 min? If the voltage difference across the light is 120V. How much light energy will the bulb give off?

3) Create an analogy that relates current and voltage to a hydroelectric dam.

4) Ovens are typically based on a 240V circuit with 30 A of current. A light bulb is based on a 120V circuit with 0.50A of current. How much more energy will an oven use over the course of an hour? Does this make sense? Why?

5) Is it possible to have a condition where an electrical voltage exists, but no electric current exists? Conversely, is it possible to have a condition where an electric current exists without an accompanying voltage? Explain your answers, and give practical examples where the stated conditions are indeed possible.

Homework

Create a chart that summarizes the circuit symbols for the following circuit parts:

•Resistor•Variable resistor•Switch (closed and open)•Light bulb•Cell•Battery of 3 cells•Motor

• Switch• Ammeter• Voltmeter• Fuse

It’s not the volts, it’s the ampshttps://www.youtube.com/watch?v=8xONZcBJh5A