Transcript Ohm`s Law - aiss-science-10

Ohm’s Law provides a basic understanding of how
voltage, current, and resistance interact in a closed
circuit.
Water Tank
Sprinkler
On-Off
Valve
Water Analogy to Electrical Circuit
Guess where the return circuit is.
Replaces
water flow
in pipe
Electron Flow
Replaces the
sprinkler
Replaces
the water
tank
L
O
A
D
Battery
Switch
Replaces on-off
water valve
See notes
below
Simple Electrical
Circuit Equivalent
to the Water
System
Voltage – The electromotive force (EMF) or potential difference
between two points in a circuitSource - DC – Batteries (dry cells, Lead
Acid, LiH, etc.) Expressed in “Volts.”
Physical example – The depth of water in a water tank.
Current – Electron flow in the circuit, from + to – side of the power
source (battery). Expressed in Amperes.
Physical example – Water flowing through a hose.
Resistance -- An electrical component that operates on voltage
applied across it. Because it does work and dissipates the energy as
heat it’s simply called a “Load” and is expressed in “ohms.”
Physical example – The lawn sprinkler.
The Three Variables
Ohm's Law is a formulation of the of voltage, current, and resistance,
expressed as:
V=IxR
Where:
V - is the Voltage measured in volts (V)
I - is the Current measured in amperes (amps)
R - is the resistance measured in Ohms (Ω)
Therefore: Volts = Amps times Resistance
Ohm’s Law Simplified
The Variables:
Divide
across
here
V
V = Voltage
Multiply
across here
I = Current
R = Resistance
I R
Solution:
Cover the unknown
variable and the
remainder gives the
solution.
How to find the Unknown Variable
Using Ohm’s Triangle
V
I R
Example: What happens to
current (I) as the resistance
(R) goes to zero?
Hold a finger over current (I)
and observe what happens
when the resistance (R)
goes to zero.
********
Current (I) becomes infinite
(actually it will be limited by
the internal resistance of the
voltage source).
An Example Using Ohm’s Triangle
Example Calculations
If Voltage = 10 volts and the Resistance starts at 10 ohms
How does the current, I, change as the resistance goes to
zero?
According to Ohm’s Law we divide voltage by the resistance
Voltage
/
Resistance = Current (I)
10 volts
/
10 ohms
= 1 amp
10 volts
/
5 ohms
=
10 volts
/
2 ohms
= 5 amps
10 volts
/
1 ohm
= 10 amps
10 volts
/
½ ohms
= 20 amps
10 volts
/
zero ohms = Unlimited amps*
2 amps
*Current is actually limited by the battery’s internal resistance (impedance).
Ohms' Law Example
Current in Amps
25
20
Voltage
15
Resistance
10
Current
5
0
1 2
3 4 5
6 7 8 9 10 11
Resistance in Ohms