Download Unit 4 - Section 13.9 2011 Ohm`s Law

Grade 9 Science - Unit 4 – Physics – Electricity
Potential Difference and Ohm’s Law
Section 13.9 Pages 568-569
Potential Difference means the difference in potential energy per coulomb of charge at one point
in the circuit compared to the potential energy per coulomb of charge an another point in the
circuit. Potential energy is voltage.
V=E/Q
Where V = potential difference or voltage
E = energy
Q = amount of charge
Question – If 42 J of chemical energy in a battery places 7.0 C of negative charge at the negative
terminal, a deficit will occur at the positive terminal. What is the potential difference between the
negative and positive terminals of the battery?
Ohm's Law deals with the relationship between voltage (V) and current (I). The relationship
states
The potential difference (voltage) across an ideal conductor is proportional
to the current through it.
The constant of proportionality is called Resistance (R).
Ohm’s Law is given by V = I R where V is the potential difference between two points which
include a resistance (R). I is the current flowing through the resistance.
Ohm’s Law states as the potential difference (Voltage) across a load (Resistance) increases, so
does the current (Current).
Ohm's Law can be used to solve simple circuits. A complete circuit is one that is a closed loop. It
contains at least one source of voltage (thus providing an increase of potential energy) and at
least one potential drop (i.e., a place where potential energy decreases). The sum of the
voltages around a complete circuit is zero. An increase of potential energy in a circuit causes a
charge to move from a lower to a higher potential (i.e., voltage).
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A fun Internet site to test your understanding of the Ohm’s Law relationship is
http://jersey.uoregon.edu/vlab/Voltage/index.html