16.5 Current Electricity and Electric Circuits

16.5 Resistance Ohm's Law
George Ohm was a German physicist that experimented with electric currents, the results of his research helped us understand the relationship between current, resistance and voltage.
Ohm found that the potential difference ( V ) in volts divided by the current ( I ) in amperes was constant with the resistance in a circuit.

Example Question
 An electric stove is connected to a 200 V supply and has a known resistance of 15 Ohms. What current will this element draw?
Given:
V = 200 v     R = 15 Ohms   I = ?       

V = IR      therefore  I = V / R                   

I = 200 V / 15 Ohms              
  =  13.34 A
Therefore, the current that the element will draw is 12.34 A.

Factors of Resistance
There are many things that effect the resistance of a circuit, such as the length and thickness of a wire, the temperature, and the material it is made of.

Table 16.4 Factors that affect resistance

Length                 The longer the conductor is, the greater the resistance will be.

Thickness            The thicker the conductor is, the lesser the resistance will be.

Material               Some materials such as copper, is better conductors then others. Resistance of a substance
                            is call resistivity.

Temperature        The higher the temperature is, the resistance tends to also increase and Vice Versa.