I have a very fundamental question, will an electric bulb glow with one point connected to the positive terminal of the electric line and the other point to earth? In my school some 10 years back I learnt that we are connecting the two points of the bulb to positive and negative to make the connection closed.

As earth is considered as a huge potential of ions it could be considered as the negative side. If my thinking is wrong then why do the LEDs glow in the tester? In the tester we touch the tail which is indirectly connected to earth.

Note I dont know what the tester is called in other countries. The Tester is a small instrument to check if the current flows in a circuit or not and is size of a pen.

  • 1
    \$\begingroup\$ In a random other country your tester is called 'spanningszoeker'. \$\endgroup\$ – jippie Nov 13 '13 at 6:58
  • \$\begingroup\$ Where do you live that your power lines provide a positive terminal? In most of the world, people have AC. \$\endgroup\$ – Kaz Nov 13 '13 at 7:20
  • \$\begingroup\$ @Kaz Friend I am software developer.i am not aware of the technical(electrical terms) though I have read in school but now I have forgotten the technical words \$\endgroup\$ – SpringLearner Nov 13 '13 at 7:41
  • \$\begingroup\$ @Kaz I believe by "positive terminal" he means the live wire, as opposed to neutral and ground wires. \$\endgroup\$ – Boluc Papuccuoglu Nov 13 '13 at 12:51
  • \$\begingroup\$ Since the Neutral-slot and the Earth-slot in the AC outlet are always connected together at the fusebox, it doesn't matter if the planet Earth is there. The "Tester" is still connected across 120VAC (or 240V 50Hz, whatever.) \$\endgroup\$ – wbeaty Dec 29 '16 at 9:46

Yes and no.

Yes, because the earth cable is connected to the neutral at some point. In some country this is done at the entry point of every buildings, in other it's earlier. Thus the circuit will be closed and the bulb will light up.

No, because in nowadays house, residual current circuit-breakers are used. If the return current is flowing through the earth cable and not through the neutral cable (>20mA typically) the breaker will break and your bulb won't work.

About your tester: The human body that touches a terminal of the light included into your tester acts as a capacitor. This is called "Body capacitance". Because the other terminal is connected to an AC source (the main), a current (very very small) flows through the tester and it lights up.

  • \$\begingroup\$ Thanks for the answer +1.Can i connect a 220v bulb to a positve terminal and I will touch the negative end standing on floor \$\endgroup\$ – SpringLearner Nov 13 '13 at 7:45
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    \$\begingroup\$ No. Dont' do that. there is a risk of electrical shock. In a tester, the small bulb is in series with a high value resistor to have a very small current. If you touch the terminal of a standard 220V light buld which has a comparatively small internal resistance, you will basically touch the main wire. Which is dangerous. \$\endgroup\$ – Blup1980 Nov 13 '13 at 7:51
  • \$\begingroup\$ So suppose if i dont have a tester to check,can I check using 220v electric bulb by connecting one point to earth and other point where I need to check \$\endgroup\$ – SpringLearner Nov 13 '13 at 7:58
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    \$\begingroup\$ No. Your circuit breaker will break because a current higher than 20mA will flow elsewhere than into the neutral wire. And you cannot add a big resistor in series to reduce the current because at very low currents, a standard light bulb will not light up. In any case, don't play with main if you don't know exactly what you are doing. At least if you want to stay alive for sure. \$\endgroup\$ – Blup1980 Nov 13 '13 at 8:13

Yes will glow, think about three phase generator that you can use without neutral or earth under one condition balance load which is impossible


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