Warm-up

Which particles move freely through metals?

a. Atoms c. Protons

b. Electrons d. Molecules

What is the charge on the following particles:

c. Proton -

d. Electron -

e. Neutron - negative

positive

neutral

8-2 Current Electricity

Describe electric current.

Identify the two types of current.

Explain how voltage produces electric current.

Calculate voltage, current, and resistance using Ohm’s Law

Electric Current

A steady flow of electrons through a conductor.

Measured in amperes or amps (A).

Variable is “I”

Direct Current (DC)Charge flows in one direction.– battery operated devices– Electrons flow from the negative to the

positive.– Opposite to direction of the current.

Alternating Current (AC)

A flow of electrical charge that regularly reverses the flow of charge.– American electricity changes directions 60

times a second.– Household current is alternating current.

Potential Difference

Also known as Voltage.

The “push” that causes electrons to flow through a circuit.

Measured in volts (V).

Variable is “V”

Resistance

Anything that slows the flow of electrons through a conductor.

Measured in ohms (W ).

Variable is “R”

Ohm’s Law

The mathematical equation that shows the relationship between current, potential difference and resistance.

V = IR

Where: I = current in amps (A)

V = potential difference in volts (V)

R = resistance in ohms (W)

Sample Problem

How many 1.5V batteries would be needed to supply 0.83A of current if the appliance offers 5.4W of resistance?

I = 0.83A

R = 5.4W V = IR

V = 0.83A(5.4 )W

V = 4.482V4.482V / 1.5V per battery = 2.988 or 3 batteries

Sample Problem

If a lamp bulb requires 5.5amps of current supplied at 110volts, how much resistance does it offer?I = 5.5ampsV = 110volts

R = V / I

R = 110V / 5.5a

R = 20W

Sample Problem

If an electrical appliance offers 24 W of resistance, and is connected to a 9.0V battery, how much current will flow?

R = 24WV = 9.0V I = V / R

I = 9.0V / 24W

I = 0.375a

Conclusion

What is the relationship between current, voltage, and resistance?