Presentation on theme: "Electrical Resistance Gr 9 Science. 4 Electrical resistance = the property of a substance that hinders electric current and converts electrical energy."— Presentation transcript:
4 Electrical resistance = the property of a substance that hinders electric current and converts electrical energy to other forms of energy. Resistor = a device used in an electric circuit to decrease the current through a component by a specific amount.
Load = a resistor or any other device that transforms electrical energy into heat, motion, sound or light.
Ohm`s Law Georg Ohm was curious about the relationship between current and force. He noticed in experiments that when the force was cut in half, the current was also cut in half. The resistance remained the same. So Ohm`s Law states that: force (V) = current (A) x resistance (Ω) or V = I x R
Therefore, current (A) = force (V) ÷ resistance (Ω) or I = V ÷ R resistance (Ω) = force (V) ÷ current (A) or R = V ÷ I
The power of an electrical machine is measured in watts. watts = voltage (volts) x current (amps)
So, Ohm`s Law also states that the ratio of potential difference to current is a constant called resistance. The unit of resistance is the ohm (Ω), which is equivalent to one volt per ampere (V∕A).
Factors that affect the resistance of wires: 1. The type of material affects the resistance. Ex., a copper wire has less resistance than an iron wire of the same length and diameter. 2. A shorter wire has less resistance than a longer wire of the same diameter and made of the same material.
3. A thicker wire has less resistance than a wire of the same length and material. 4. Resistance increases with temperature. A cold filament has less resistance than a hot filament.
A superconductor is a material through which electric charge can flow with no resistance. A superconducting wire does not transform electrical energy into heat. Therefore, using a superconducting wire would vastly increase the efficiency of supplying electrical energy.
A resistor that obeys Ohm′s Law has constant resistance. A resistor that does not obey Ohm′s Law is called a non-ohmic conductor. Ex., in the filament of an incandescent bulb resistance increases as the filament′s temperature increases