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why current will not flow from battery if I connect positive terminal of battery to ground even when there is potential difference

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  • $\begingroup$ How did you "connect positive terminal...to ground?" What is the negative terminal of the battery connected to? In which connection did you measure the current? Between which nodes did you measure the voltage? A circuit diagram would help readers to understand what you are asking. $\endgroup$ – Solomon Slow Apr 13 '18 at 14:01
  • $\begingroup$ negative terminal is not connected to anything however potential difference exists between positive terminal and ground but no current is there through the resistor which connects the positive terminal and ground. $\endgroup$ – Sai Charan Reddy Apr 13 '18 at 15:15
  • $\begingroup$ If you connect the positive terminal to the ground with a wire, then there is no p.d. between the terminal and the ground (assuming the wire is not long enough to act as an antenna). $\endgroup$ – The Photon Apr 13 '18 at 16:18
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I connect positive terminal of battery to ground...

[The] negative terminal is not connected to anything.

If the negative terminal of the battery is not connected to anything, then no current can flow through the battery. Current can only flow around a complete circuit (i.e., it can only flow around a closed loop).

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  • $\begingroup$ but its violating the rule that current flows under applied potential difference $\endgroup$ – Sai Charan Reddy Apr 13 '18 at 17:36
  • $\begingroup$ @SaiCharanReddy I think you misunderstand that law. There will be no current flow if there is no path/medium through which mobile charge carriers (e.g., electrons) can move. The strength of the electric field makes no difference.* $\endgroup$ – Solomon Slow Apr 13 '18 at 18:00
  • $\begingroup$ *...unless the field is so strong that it creates a conductive path by ionizing whatever matter stands in the way. When that happens in air, we call it an electric arc. But, it takes many thousands of volts (way higher than the voltage of a battery) to make that happen. $\endgroup$ – Solomon Slow Apr 13 '18 at 18:02
  • $\begingroup$ but the wire is a conductor which connects positive terminal of battery and ground acts as medium or path. $\endgroup$ – Sai Charan Reddy Apr 13 '18 at 18:04
  • $\begingroup$ You said, in reply to a comment that I made on your original question, "the negative terminal [of the battery] is not connected to anything." A path to "ground" is not necessary for current to flow. A path that makes a closed loop is necessary. If the negative terminal of your battery is not connected to anything, then the battery is not part of any closed loop, and current can not flow through through the battery. Which means, no current can flow in to or out of the other terminal. $\endgroup$ – Solomon Slow Apr 13 '18 at 18:48
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Since the negative terminal is very small, the capacitance between the terminals does not change much, even when the negative terminal is connected to ground. So, to maintain the same voltage between the terminals, no current would need to flow.

If the negative terminal was also connected to a large object, preferably close to ground, the capacitance between the terminals would increase and the current would flow.

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When you connect the positive terminal to ground, the potential difference, if there was any at all, vanishes. The terminal becomes part of the ground.

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