1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Alternating current and Direct current?

  1. Jun 8, 2012 #1
    I have this Question about toaster and electric kettle and I just want to know if they are working on alternating current or direct current.

    Does a Toaster works on alternating current or direct current? and why?

    Does a electric kettle runs on alternating current or direct current? and why?

    Do you know any kitchen equipment that runs on direct current?

    Tanks soo much for your helps
  2. jcsd
  3. Jun 8, 2012 #2


    User Avatar

    Staff: Mentor

    I know of no major kitchen equipment that runs on DC.
  4. Jun 8, 2012 #3
    Most kitchen appliances require a DC(direct current) for them to work as this is a constant current, while AC fluctuates between different directions it travels in the circuit which can stuff up appliances. AC current is used as it is easy to transport over long distances and there is less power loss. Appliances therefore usually have what are called transformers, rectifiers, capacitors and voltage regulators. these help to get the large AC voltage into a small smooth DC voltage. Transformers bring down the large AC voltage to a smaller AC voltage. rectifiers make sure that current only travels through one direction of the load. capacitors are like batteries which supply voltage when the AC is at a low point, this creates a ripple voltage. Voltage regulators consist of zener diodes which cut off any excess voltage and smooth the AC into an almost DC, for the appliance to use. =D
  5. Jun 8, 2012 #4
    while most appliances require DC, things like light bulbs can operate on AC, which menas the lights switch on and off. This is where i live at 50hz which is like it going on and off ever 10 milliseconds, so we don't really notice. I'm not sure about any other appliance, usually the more sophisticated they are, the more even direct current they need.
  6. Jun 8, 2012 #5


    User Avatar

    Staff: Mentor

    Which appliances are you thinking of? The ones with motors surely require AC because the design of an electric motor depends on whether it's to be used with AC or DC, and household electricity (in the USA at least) is always AC. I suppose things like toasters or electric ovens (the ones with resistive heating elements, not microwaves) could use either AC or DC in principle.
  7. Jun 9, 2012 #6
    apperciate your answers, But the question is why a toaster works on ac and why kettle works on ac?
  8. Jun 9, 2012 #7
    Appliances which behave as a resistive load, eg kettles, toasters, electric fires (without fans), kitchen ranges etc, can in theory be run on DC. DC generates the same heating power as AC with the same voltage once the AC voltage is quoted in RMS. In practice however, switches in these appliances may burn out prematurely as arcing may occur because of the unidirectional nature of DC. When AC is switched, the arc or spark on switching tends to extinguish as the voltage falls to zero half way through the cycle.
    Devices which incorporate transformers such as power supplies, and induction motors for example washing machines, driers, fridges and freezers must only be powered on AC. Appliances which use universal motors e.g. drills, vacuum cleaners etc should run on DC.
    Last edited: Jun 9, 2012
  9. Jun 9, 2012 #8
    Almost no kitchen appliances require DC and very few have transformers, rectifiers, etc. Many are made up of nothing more than simple resistive heaters (which don't care about AC or DC) or AC motors (which require AC and won't function on DC) and switches.

    Some appliances have electronic timers, clocks, etc which need a small DC power supply to run those electronics. Transformers used to be popular, but these days switching supplies are smaller and often cheaper (less copper and iron used). The only appliance that I can think of which requires DC for its primary function is the microwave, where high voltage DC is required to run the magnetron...and this is generally produced using a transformer, which requires an AC input.

    Because what you get out of the wall outlet is AC and there's no benefit to converting to DC. This would involve adding rectifiers and filter capacitors that would add expense and complexity, make no difference to the heating elements, and themselves waste some power.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook