# 9 Volt battery connected with no resistance but current is not 9 A?

As per Ohms law , V = IR OR I = V/ R

So if I set R to 0 , then V should be equal to I ?

However when I connect 9 Volt battery poles to each other with multimeter in between the reading says 0.2 A.

• your 9v battery is flat. – Jasen Jul 30 at 8:00
• Mathematics 101. – Andy aka Jul 30 at 8:04
• @jasen what is flat ? – Mr Coder Jul 30 at 8:05
• Your math is wrong. I = 9/0 which is "infinity" or cannot be computed. However, resistance is never zero. And there is a concept you did not address, which is the internal resistance of a battery. – mkeith Jul 30 at 8:09
• @MrCoder: "101" from a common numbering system for college/university level courses. 100 is the base level, usually first year. 101 is typically the first year introductory course for a given subject. "Math 101" is therefore just a fancy way of saying "basic math." – JRE Jul 30 at 8:12

Fortunately for you, batteries have internal resistance. If they hadn't then you would have either blown your meter's current limit fuse or destroyed your meter.

Never short-circuit a battery or power supply with an ammeter. Always connect it in series with the load.

You can model your battery as an "ideal" 9 V battery with a series resistance. From you measurement you can calculate that the battery's internal resistance. $$\ R = \frac {V}{I} = \frac {9}{0.2} = 45 \ \Omega \$$.

So does it mean if I short circuit 220 V (in house voltage), then reading should be 220 amps, since now there is no battery hence no internal resistance?

If there is no internal resistance on your 220 V supply then $$\ I = \frac {V}{R} = \frac {220}{0} = \infty \ \text A \$$.

Never short out a supply like that. Explosive amounts of energy can be released. (Look up "arc flash" on YouTube.) If you try it with your multimeter the results could be lethal.

• so does it mean if I shortcircuit 220V (in house voltage) , then reading should be 220 Amps , since now there is no battery hence no internal resistance ? – Mr Coder Jul 30 at 8:34
• Sigh 2.0........ – Bart Jul 30 at 8:43
• @MrCoder See mkeith's comment above. Your math is incorrect. – HandyHowie Jul 30 at 8:43
• @HandyHowie thanks I made an error in calculations. – Mr Coder Jul 30 at 9:19
• @MrCoder: See the update. – Transistor Jul 30 at 9:24

First, as already said- don’t ever attempt to deliberately short any power source unless you are trying to obtain a UL rating for a device- you run a high risk of fire or (perhaps minor) explosion! I once worked for a power supply manufacturer and was assigned to do this sort of work one week- the supply was behind a blast shield for this reason.

Second, the ammeter itself has resistance in addition to the wires connecting it as well as the battery itself. There’s no way in a practical circuit to achieve zero resistance however close you might get and your current reading would only be 9A if the total resistance was exactly 1 ohm.

For internal resistance of typical battery types, see this article (the table therein shows a 9V zinc carbon battery is typically 35 ohms):