Download Ohm*s Law

Ohm’s Law
http://phet.colorado.edu/sims/ohms-law/ohmslaw_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

V
To calculate resistance, R: put your
finger over R, this leaves you with V
over I, so the equation is R = V/I
Triangle
I
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. 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.
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