20.2 Ohm's Law: Resistance and Simple Circuits

20.2 Ohm's Law: Resistance and Simple Circuits

• The equation can be used to calculate the drift velocity.
• The charge of an electron is given.
• The formula can be used to calculate the area of a cross-section of the wire.
• The periodic table shows that the atomic mass of copper is 63.54 g/mol.
• We can use the two quantities and Avogadro's number to determine the number of free electrons.

• The density of free electrons in copper is calculated first.
• There is one electron for every copper atom.
• The number of copper atoms is the same.

• The negative charges are moving in a different direction than conventional current.

• We can think of batteries, generators, wall outlets, and so on, which are necessary to maintain a current.
• The devices create a potential difference and are referred to as voltage sources.

• An electric field is created when a voltage source is connected to a conductor.
• The electric field exerts force on charges.

• The voltage applied to a substance affects the current that flows through it.

• It can be seen as a cause-and-effect relationship.
• This is an empirical law that has been observed.
• Sometimes a linear relationship doesn't happen.

• The substance has moving charges and atoms that transfer energy to the substance.

• If resistance doubles, current is cut in half.

• The relationship is called Ohm's law.
• This form of Ohm's law defines resistance for certain materials.
• Hooke's law is not universally valid.
• Good conductors like copper and aluminum are included.
• Ohmic materials have a resistance that is not dependent on current or voltage.
• Even if the object's resistance is small, it's still called a Resistor.

• The schematic is shown in Figure 20.8 The wires connecting the source of the power to the resistance can be assumed to not have resistance at all.

• A simple electric circuit in which a closed path for current to flow is supplied by conductors is represented by the red parallel lines.
• Any resistance in the connections to the voltage source is represented by the zigzag symbol.

• We can use Ohm's law to find resistance.

• The small resistance is larger than the cold resistance of the headlight.
• The bulb has a lower resistance when it is first switched on because it draws more current during its brief warm-up period.

• Resistances range in size.