Power in Circuits Video Lessons

Concept

# Problem: The circuit shown has four identical light bulbs and an ideal batterya. Rank the brightness of the bulbs. Explain your reasoning.b. A wire is now added to the circuit as shown.i. Does the brightness of bulb C increase, decrease or remain the same? Explain your reasoning.ii. Does the brightness of bulb A increase, decrease, or remain the same? Explain.iii. Does the current through the battery increase, decrease, or the remain the same? Explain.

###### FREE Expert Solution

a.

Since all the bulbs are identical, we take the resistance of each bulb to be R.

Power is expressed as:

$\overline{){\mathbf{P}}{\mathbf{=}}{{\mathbf{i}}}^{{\mathbf{2}}}{\mathbf{R}}}$

From this equation, the current is directly proportional to power.

Ohm's law:

$\overline{){\mathbit{i}}{\mathbf{=}}\frac{\mathbf{V}}{\mathbf{R}}}$

We need to determine the current flowing in each branch.

Let's re-label the figure as below.

The currents are drawn based on Kirchhoff's junction rule.

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###### Problem Details

The circuit shown has four identical light bulbs and an ideal battery
a. Rank the brightness of the bulbs. Explain your reasoning.

b. A wire is now added to the circuit as shown.

i. Does the brightness of bulb C increase, decrease or remain the same? Explain your reasoning.ii. Does the brightness of bulb A increase, decrease, or remain the same? Explain.
iii. Does the current through the battery increase, decrease, or the remain the same? Explain.