Question

Conceptual: Consider a lightbulb attached to a battery with wires. How must the light bulb be connected in order for it to light? Identify the relevant parts of the bulb and battery and explain the concept of

Answer 1

Please refer the figure below:

How will the bulb glow?

In the picture bulb is conneted across terminals A and B.
Voltage source is connected at C and D. The longer line (at C) being positive end.
K is switch, which turns on and off.

If this arrangement is made:
1) Bu connecting two ends of bulb to two connecting wires.
2) Conncecting an end of one of those connecting wires via switch K, to positive end of voltage source.
3) Connecting other connecting wire to negative end of voltage source.

We can obtain the required circuit. Now, to glow the bulb, we close the switch K.

What is potential difference?
In the voltage source (here battery), we have two ends positive (C) and negative (D). Positive end has lack of electrons and hence collection of positive charges.
The negative end has excess of electrons or negative charge.

Potential difference is said to be difference in potentials (produced due to accumulation of charges of opposite nature at both ends). So, if at C, potential is say P₊ and at D it is P_-
Then potential difference = V = P₊-(P_-)  in volts.

How does potential difference make the bulb light?

Whenever there is a potential difference across a conducting path (here: the circui with switch closed), we have electrons flowing from lower potential D to higher end C, so as to undo the potential difference.

The electrons constituting electronic current have to flow through the bulb filament which comes in their path. So, when electrons flow from B to A in the filament, we have the resistance of bulb filament obstruct their flow. This obstruction leads to collisions between metail filament ions and electrons, and hence production of heat energy, and subsequently light energy.

This light energy lightens the bulb.

When F5 and F6 used?

Voltage across source is was 1.016 volts, then change in potential across bulb is 1.016 V.
Voltage across source is was 0.020 volts, then change in potential across bulb is 0.020 V.

This quantity can be measured by attaching a device called voltmemer across ends of the bulb. Voltmeter shows the reading in its scale.

When a single electron moves from B to A across bulb, it is going from negative end to positive end and hence decreasing potential, and subsequently potential energy.

So, it is loss of potential energy.

Reason: When we separate two unequal charges,we do work that is stored as potential energy. Here, that work is done by battery.
But when a conducting path is connected across ends of battery, then electrons flow to undo the potential diference. Hence, work done by battery to create the potential energy gap slowly decreases.
Hence, potential energy decreases.