How does the ampere work?

Discussion in 'General Electronics Chat' started by Siva Manasan, Dec 12, 2017.

  1. Siva Manasan

    Thread Starter New Member

    Nov 14, 2017
    I am so confused about this ampere thing.

    Here are my questions.

    1.A DC battery can deliver any amount of ampere we want(Before the battery burns out).For example, an led with 5 voltage and 1 amp rating can work in a battery of 9 v and a motor with the same voltage but higher ampere can also work in this battery.Right?

    2.In the phone adapter(I am trying to charge my iPhone from a car igniter.), it is said to deliver 5v at 1A.Here why do they even mention the ampere if it is not needed and it all depends on the phone itself(I am thinking why can't the phone take ampere it needed like the led.I am not giving specific current to led.It is taking what is needed.)

    3.Is it safe to measure the ampere of the phone adapter(Which is said to deliver 1 A of current) with my multimeter?(I tried to measure ampere of a battery and the multimeter went crazy.)

    4.In this video he is touching a 200000 volt with his bare hand and he is still alive because of law ampere.My question is how he is able to control the ampere here if you can't control in the wall socket or even battery.(I thought that it has to do with ohm's law and series connection where we can divide the ampere by introducing a high resistance to the circuit.)

    5.Is it safe to charge a phone with 5v and 1A rating with a power source of 5 volts and 2 A

    6.In this image [​IMG] different currents are said to have different effects.Is it true that when I touch the AC power supply how much ampere is flowing through the body is determined by the resistance of the skin.

    7.When I measured my laptop charger for AC current I was able to get about 50V(Is this because of improper earthing) but when I touched it I couldn't feel the electricity, Why is that?(I did some calculations and found that the current passing is about 0.00025 so it may be not fatal.Is this correct)

    8.I heard about the electric man in India who can conduct a huge amount of electricity through his body and even turn on a grinder(LINK)and they said that he has a lot of resistance about 1.5 million ohms.My question is how does he do this(Because if he has huge resistance how does electricity even pass through his body)Can I do this trick if my skin had a very little resistance (So the current will go through my skin{My skin would behave as a super conductor})

    9.why can't I use the power(P=V*I) to find out whether a human can survive an electrocution.

    Thank you for all your contributions.I am so amazed by the power of all about circuits community.Any help is appreciated.
  2. LesJones

    Well-Known Member

    Jan 8, 2017
    1 A battery cannot deliver an unlimited current. ( The ampere is the unit of current jusat like the metre is a unit of distance.) The current a battery can supply is limited by it's internal resistance.

    2 1 amp is the MAXIMUM current that the power supply can provide.

    3 You measure the current flowing THROUGH a wire not the potential difference between two two points. If you connect a multimeter ACROSS the terminals of a battery the current value that you read will be the battery voltage divided by its internal resistance. You need to learn the most basic thing about electricity. OHMS LAW. If you understood that you would not be asking these questions. Use Google if you do not have your science books from when you went to school.

    4 Again this is back to understanding ohms law. Voltage is a relative term as it must be measured relative to some other point. (Just like measuring distance. Which has to be from some other point.) If you are insulated from one side of a voltage source then no current can frow through you when you touch the other side of the voltage source.

    5 Yes.

    6 Skin resistance is one factor.

    7 You question does not make sense. It is like saying a piece of string is 2 degrees centagrde long.

    8 I do not believe the story.

    9 P = V*I is just a relationship. you would also need ohms law to determine the current.

    Until you REALY UNDERSTAND ELECTRICITY assume that any voltage above 12 can be dangerous. In some situations even 12 volts could kill.

  3. xox


    Sep 8, 2017
    1) No. A battery has significant internal resistance which effectively limits the amount of current (amps) that it can deliver. Capacitors, on the other hand, typically have very little internal resistance and thus can dump a large amount of current.

    2) Actually, the load determines how much is consumed. The amp rating of a battery is just a statement of the maximum deliverable current. Incidentally, you can find the effective internal resistance of a 5V 1A charger using Ohms law (R = V/I), so 5/1 = 5 ohms.

    3) Just don't exceed the multimeter's highest current setting. And of course you want to measure the current in series, not parallel.

    4) Think of a 5 volt battery connected to a 1,000,000 ohm resistor in series with an LED. If the forward voltage of the LED is 2.2 volts then the maximum current that the battery can deliver is (5 - 2.2) / 1000000 = 2.8 microamps. The LED would likely require about 1000 times more current to even begin to glow. By the same token, a 200000 volt object can be safely touched if a high enough resistance exists in between.

    5) Yes, just as it would with a 5V 100000000000000000A charger.

    6) Assuming the intervening resistance described above (#4) is negligible, the voltage just must be high enough to overcome the resistance of the body and whatever other external conditions apply (moisture, sensitivity of the individual, etc).

    7) Be careful; avoid touching electrical circuits directly until you know what you're doing! Anyway, it's really the flow of current that is felt - not voltage.

    8) Not sure, looks like a hoax to me though.

    9) Remember, it's the amps that kill you. ;)
    cmartinez likes this.
  4. crutschow


    Mar 14, 2008
    As noted, Ohm's law, I = V/R, will answer many of your questions, that is, the current in amps through a circuit is proportional to the applied voltage divided by the circuit resistance in ohms.