After going through multiple youtube videos and some articles I'm still having trouble imagining voltage.

If we measure across a battery's terminals we will see electrical potential. This is caused by the collection of negative particles on the negative terminal and positive particles on the positive terminal. Since these are being "kept apart", there is some work being done to hold them where they are, and therefore potential energy. The difference in potential energy between the two terminals is our voltage.

When we connect a battery to a simple circuit consisting of a lamp (for example), we can measure the two points on the conductor using a voltmeter and see 0V. Since the electrons are being "pulled" towards the positive terminal (in the same sense that gravity pulls a dropped object downward), there is no work being done to prevent the from traveling to the positive terminal, therefore the difference in the potential energies between the two points is 0.

Now when we measure across the lamp in the circuit we will once again see a voltage. I think this is where I get confused. The lamp isnt part of the conductor, and therefore there is voltage - this is where my book leaves off.

Using my reasoning from above - is this because on the positive end of the lamp, it's connected to the positive terminal and has a higher positive charge than the rest of the conductor? This would explain why there is a measurable potential difference. If so, what happens inside of the lamp with the potential energy? Some of it must be turned to heat?

  • 2
    \$\begingroup\$ You can treat the voltage as a height. youtu.be/ZSrzvoJcaJ8 To measure the voltage we need two points in the space. One of this point is treated as a reference point. We have a very similar situation when we try to measure a height of an object. We need a reference point. The most common reference point is "above mean sea level". But when you measure the height of the table in your house the floor now becomes your reference point. electronics.stackexchange.com/questions/370488/… \$\endgroup\$
    – G36
    Commented Aug 15, 2018 at 19:37
  • \$\begingroup\$ Since these are being "kept apart", there is some work being done to hold them.. No work is being done, the same can be said of a weight held at a height. The state of potential energy does not require any additional energy to maintain the state. \$\endgroup\$
    – lakeweb
    Commented Aug 15, 2018 at 20:48
  • \$\begingroup\$ @lakeweb I see, I misspoke. Would a better way to phrase that be We have done some work to move them apart, and this work is stored as potential energy? \$\endgroup\$
    – CL40
    Commented Aug 15, 2018 at 21:08
  • \$\begingroup\$ Yes. Like it takes work to charge a battery. \$\endgroup\$
    – lakeweb
    Commented Aug 15, 2018 at 21:54

1 Answer 1


You have a fundamental misunderstanding about voltage. A voltage difference isn't caused by an imbalance in the amount of charge, it's caused by a difference in the amount of energy available from the charge.

As charge passes (i.e. current flows) through an incandescent lamp it loses electrical energy, which is converted to heat and light. The density of electrons is the same at both ends of the filament, but the charge entering the filament has more energy than the charge leaving the filament.

  • \$\begingroup\$ So as it flows through the lamp it imparts the joules stored (in the form voltage - joules per charge) in to the parts of a lamp. The density of electrons is the same at both ends because what comes in must come out, and all the electrons are doing is traveling "through" the lamp, and to do that they must perform some work, causing their electric potential to go down. We should be able to see a voltage drop measuring the point voltage on the other end of the load then. Am I understanding this more correctly now? \$\endgroup\$
    – CL40
    Commented Aug 16, 2018 at 3:38
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    \$\begingroup\$ Yes, except you need to be very careful when you use words like "point voltage". Voltage is always measured between two points and is actually a voltage difference. In many cases we assume that some point in a circuit is "ground" and all voltages are measured with respect to ground. So, we might say "voltage at point X" meaning "voltage between X and ground". \$\endgroup\$ Commented Aug 16, 2018 at 11:23

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