Calculating Electricity

Ohm’s Law and Power Equation

Ohm’s Law

Relationship between voltage, current, and resistance

Ohm’s Law

E represent voltage, (E is short for electromotive force)

I represent current measured in amperes

R represent resistance measured in ohms

Ohm’s Law

Relationship between E, I, and R

E = I x R

Ohm’s Law

Assume that 10 A of current flows in circuit having a total resistance of 11 ohms. What is the source voltage?

E = I x R

Ohm’s Law

Using the formula

E = I x R

E= 10 A x 11ohms

E = 110 volts

Ohm’s Law

Assume that there are 6 amps of current flowing through a 120 volt circuit. What is the resistance?

R = E ÷ I

Ohm’s Law

Using the formula

R = E ÷ I

R = 120 volts ÷ 6 amps

R= 20 ohms

Ohm’s Law

Assume that you need to know how much current is flowing through a 115 volt circuit containing 25 ohms of resistance. What is the amperage of the circuit?

I = E ÷ R

Ohm’s Law

Using the formula

I = E ÷ R

I = 115 volts ÷ 25 ohms

I = 4.6 amps

Power Equation

Relationship between watts, amps, and volts

Power Equation

P for watts (P represents power) I for amps E for volts

Power Equation Relationship between P, I, and E

P = I x E

Power Equation

Assume that .83 amps of current flows through 120 volt circuit. How many watts of electrical power are being used?

P = I x E

Power Equation

Using the formula

P = I x E

P = .83 amps x 120 volts

P = 99.6 watts of power

Power Equation

Assume that there are 5, 100 watt light bulbs being operated on a 115 volt circuit. How many amps of current are flowing through the circuit?

I = P ÷ E

Power Equation

Using the formula

I = P ÷ E

I = 500 watts ÷ 115 volts

I = 4.35 amps of current

Power Equation

Assume that there is a 1200 watt coffee pot pulling 10 amps. What is the source of voltage?

E = P ÷ I

Power Equation

Using the formula

E = P ÷ I

E = 1200 watts ÷ 10 amps

E = 120 volts