I have a simple circuit running off a battery powering a lightbulb (bulb A). If I add another light (bulb B) in series with bulb A I can expect that the voltage across bulb A will _________ and bulb A will shine___________.

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BlackTom AI · Accepted Answer

When evaluating a circuit question like this, it helps to recall how series circuits work for resistors (or lightbulbs): the same current flows through all components, while the total resistance is the sum of individual resistances.

Option 1: 'all of them' — This cannot be true because at least one of the described outcomes (voltage across bulb A increasing, or bulb A brightness increasing) contradicts how series circuits behave. Adding another bulb in series increases total resistance and changes the current, so not all aspects stay the same.

Option 2: 'decrease, dimmer' — This aligns with the fundamental behavior of series circuits. The second bulb adds another resistance in the path, so the total resistance goes up. With a fixed battery voltage, the current through the circuit drops (Ohm's law: I = V / R_total). Since the current is the same through both bulbs in series, the current through bulb A decreases, and the voltage drop across bulb A (V_A = I × R_A) also decreases if bulbs have similar resistance. The reduced current and reduced voltage across bulb A cause it to shine dimmer.

Option 3: 'increase, brighter' — This is incorrect. Adding another bulb in series does not increase current; it increases total resistance, which reduces current. Therefore neither the current nor the brightness increases.

Option 4: 'stay the same, the same as before (but the battery will run out faster)' — This is also incorrect. The current in a series circuit changes when you change the total resistance. The brightness would not stay the same because the current and the voltage distribution across bulbs change with the added resistance. The statement about the battery running out faster is misleading: while total energy delivery over time depends on current and resistance, the key point here is that the current and voltage across bulb A do not stay the same when a second bulb is added.

In summary, adding bulb B in series increases total resistance, lowers current, and reduces the voltage drop across bulb A, making it dimmer. The option that reflects 'decrease, dimmer' is the correct interpretation.

Physics Honors-Henrikson Unit 11 and part of 12 Test part 1

I have a simple circuit running off a battery powering a lightbulb (bulb A). If I add another light (bulb B) in series with bulb A I can expect that the voltage across bulb A will _ and bulb A will shine___.

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