Both batteries in FIGURE Q27.7 are ideal and identical, and all lightbulbs are the same. Rank in order, from brightest to least bright, the brightness of bulbs a to Explain.
The rank in order, from brightest to least bright light bulb is
The brightness of the bulb depends upon the amount of energy per second dissipated as light through the bulb when current pass through it.
The equation for the power of the bulb is,
Here, is the current in the circuit and is the resistance of the bulb.
An ordinary light bulb dissipates surprisingly little power, in comparison with bulbs and . Both bulbs b and c have a resistance that doubles that of an individual bulb.
To make sure you are convinced, let us point out that the power dissipated in a resistor when the potential difference is given is,
Therefore, we can conclude that both bulbs and dissipate the same amount of power. Due to their identical currents and resistances, following can be concluded.
The rank is,
Hence, the rank in order, from brightest to least bright light bulb is
75. A capacitor is charged to , then connected in parallel with a resistor. The capacitor will discharge because the resistor provides a conducting pathway between the capacitor plates, but much more slowly than if the plates were connected by a wire. Let be the instant the fully charged capacitor is first connected to the resistor. At what time has the capacitor voltage decreased by half, to ?
Hint: The current through the resistor is related to the rate at which charge is leaving the capacitor. Consequently, you'll need a minus sign that you might not have expected.
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