Electric Current Charges on the move!

What makes a charge move? Electric current moves due to potential difference Electric potential difference is measured as voltage – Potential difference is measured in volts (V) The flow of charges due to potential difference is current electricity

What makes charges move? Charges must have a pathway to move Pathway is called a circuit Circuit must have certain parts: – Source (area of high potential) – Path (usually wire) – Load (something that does work using the moving charges) – Sink (area of low potential)

What makes charges move? Source of potential difference may be direct current Batteries produce direct current due to a chemical reaction Voltage produced by chemical reaction can travel through wire to load Two kinds of battery: – Dry cell: two elements and chemical paste – Wet cell: two metals and liquid electrolyte

What makes charges move? Source of potential difference may be generator Generator moves wire in magnetic field to create alternating current (AC)

How many charges move? Amount of moving charges is called current Current measured in Amperes (amps) (A) Current is number of charges moving past in one second (Coulombs/sec)

Why do charges lose potential? Resistance: similar to friction, resistance slows down charges Resistance measured in Ohms ( Ω) Size of wire affects resistance –Longer wire has more resistance –Thicker wire has less resistance Load in the circuit is a resistance

Ohm’s Law Relates current, potential difference, and resistance Current = voltage / resistance I = V/R We can use our circle with this!

Ohm’s Law Example Calculate the voltage difference across a 25 Ω resistor if a 0.3 A current is flowing through it? Step 1: What do we know? –Know R = 25 ΩI = 0.3 AV = ? Step 2: What equation will we use? V = I R

Ohm’s Law Example Continued Step 3: Plug in info! – V = (0.3 A)(25 Ω) Step 4: Do the math – V = 7.5 V Step 5: Check for units!