Ohm’s Law http://phet.colorado.edu/sims/ohms-law/ohms-law_en.html

To calculate voltage, V: put your finger over V, this leaves you with I R, so the equation is V = I × R To calculate current, I: put your finger over I, this leaves you with V over R, so the equation is I = V/R To calculate resistance, R: put your finger over R, this leaves you with V over I, so the equation is R = V/I V I R Triangle

V=I x R V = voltage in volts (V) I = current in amps (A) R = resistance in ohms (Ω) For most electronic circuits the amp is too large and the ohm is too small, so we often measure current in milliamps (mA) V=I x R

1 milliampere = 0.001 amperes KHDMDCM or KHDADCM mA  A

I=q/∆t I= intensity q= charge (C) ∆t= time interval Current Intensity

The light in the girls washroom requires a current of 40 amps The light in the girls washroom requires a current of 40 amps. What is the charge needed for 60 seconds of electricity? I=q/∆t =40 A x 60s =2400 C Example

The microwave requires a current of 80 A The microwave requires a current of 80 A. What is the charge needed to heat my lunch for 2 minutes? I=q/∆t =80 A x 120s =9600s Example 2

How many minutes has elapsed if 24000 C of charge pass through a circuit with a current of 1.6 A? I=q/∆t 24000 = 1.6/ ∆t 24000/1.6 = ∆t =15000 s =250 minutes Example 3

What is the voltage across a 50 Ω resistor with a current of 400 mA? 400mA= 0.4 A V=IR V= 50 Ω x 0.4 A V= 20 volts Ohm’s

What is the resistance if a circuit has 228 volts and a current of 38 mA? 38 mA= 0.038 A R = V/I R = 228 V / 0.038 A R = 6000 Ω Ohm’s