Electric Current

In this session we will,

• Review how we measure electric charge

• Discuss voltage and electric current

• Look at electric current in batteries

• Review Ohm’s Law

Before we begin, let’s discuss. .. .

• How do materials develop electric charge?

• Under what conditions does electric charge flow?

Coulombs

• Coulomb = standard unit of electric charge• In other words, the amount of electric charge

possessed by an object is measured in coulombs.

• One coulomb = 6 billion billion electrons, or about the amount of charge that flows through a 12-watt light bulb. – Shows you how tiny electrons are

Coulomb’s Law

Volts

• Voltage exists when there is an imbalance in charge

• If two objects have different amount of charge, there is voltage between them

• For example, standard battery has a voltage difference of 1.5 volts between its positive and negative terminals

• Volts expressed in joules/coulomb

Review To This Point

• In a 12-volt car battery, every coulomb of charge that moves from one side to the other does ________ joules of work.

Ohm’s Law

• Electric current is driven by ________.

• Electric current is measured in ______, which is dependent on _______ and ______.

• Electrical resistance is measured in ______.

• Ohm’s Law: I = V/R, where I is amperes, V is voltage, and R is resistance

Ohm’s Law Triangle

• To calculate voltage, V: put your finger over V, this leaves you with I R, so the equation is V = I × R

• To calculate current, I: put your finger over I, this leaves you with V over R, so the equation is I = V/R

• To calculate resistance, R: put your finger over R, this leaves you with V over I, so the equation is R = V/I

Ohm’s Law Practice

• 1) 3 volts is applied over a 6 ohm resistor. What is the current in amperes?

• 2) A lamp connected to a 6 volt battery passes a current of 0.06 amperes. What is the lamp’s resistance?

• 3) A 1200 ohm resistor passes a current of 0.2 amperes. What is the voltage?

Questions?