Electricity and Magnetism:Ac vs DC

Mr D. Patterson

Outcomes• distinguish between direct and alternating

currents and potentials, and apply Ohm’s law this will include applying the relationship:

DC• DC is an acronym for direct current• A direct current is formed when charges flow

in only one direction under the influence of an EMF

AC• AC is an acronym for alternating current• An alternating current is formed when charges

repeatedly change direction as they flow. This is formed by an EMF which alternates in polarity

The EMF source determines the current

Ohm’s law• Ohm’s law defines the relationship between

voltage, current and resistance.

• This can be applied to both DC and AC circuits

Ohm’s Law: DC

What is the current leaving the battery?

12 V

100 Ω

300 Ω

150 Ω

Ohm’s Law: ACWhat is the current leaving the

power source?

This question is not as straight forward as both voltage and current vary with time.

100 Ω

300 Ω

150 Ω

RMS values

Ohm’s Law: ACWhat is the current leaving the

power source?100 Ω

300 Ω

150 Ω