Note: to ensure you are well prepared for the quiz, you must be able to complete the following problems as if they were the quiz.
That means no help, no notes, no friends, no extra time etc. If you cannot understand these problems the first time you
attempt them, you are not prepared!
1. If the same capacitor were discharged through two different types of bulbs, what can you conclude about the
bulbs which stay lit the least amount of time?
They must have the least resistance. They also have the greatest conductance.
2. Which has the thickest filament – a high-resistance or a low-resistance bulb?
A low-resistance bulb, like a round bulb.
3. What are two observations which can be used to indicate flow rate?
Bulb brightness and compass deflection.
4. When more bulbs are added to a circuit, is there always more total resistance as a result?
Explain.
If more bulbs are added in series, the total resistance increases. But if more bulbs are added in
parallel, the total resistance is less.
5. What experiments suggest that wires have essentially zero resistance?
1) Adding more wires in series with a lit bulb does not change the brightness of the bulb so the
wire must have little or no resistance.
2) Shorting out a bulb causes a second bulb in series to become much brighter, so the wire has
much less resistance than the shorted out bulb.
3) Tapping a wire on the terminals of a charged capacitor will quickly discharge it, even if the
wire is tapped for only a brief instant – so it must have very little resistance.
6. Which lasts a longer time during capacitor discharging -- compass deflection or bulb
lighting? Explain why this occurs.
Compass deflection lasts longer than bulb lighting. This makes sense because bulb lighting may
be too dim to be observable toward the end of discharging when the flow rate is small.
Compass deflection is a more sensitive indicator as the flow rate decreases toward zero. But
bulb lighting is a less sensitive indicator because the light becomes redder and eventually infrared, i.e. invisible.
7. List in order of resistance from lowest to highest: round bulbs, long bulbs, connecting wires. Describe the
experimental evidence for your choices.
Wires < round bulbs < long bulbs. Long-round evidence: Longs remain lit longer than rounds
during discharging with same amount of charge -- or longs produce less compass deflection
than rounds in an otherwise identical circuit. Round-wire evidence: Wires produce
instantaneous discharging.
8. In the circuit shown below, bulb A and bulb B are identical and have high resistance.
a. Draw arrowtails and starbursts on the bulbs in the figure on the left.
b. A third identical bulb C is added to the circuit as shown on the right. Draw arrowtails and starbursts on that
diagram, and fill in the blanks below:
i. Bulb A will __2_ (1) become brighter (2) become dimmer (3) stay the same.
ii. Bulb B will __2__ (1) become brighter (2) become dimmer (3) stay the same.
9. A capacitor is charged through two bulbs (on the left) and then discharged through a single bulb (on the right).
Show appropriate starbursts and arrowtails for each circuit, and mark each of the following statements as True or
False (T or F). If a statement is False, re-write it as a correct statement.
a. _T___ The same amount of charge flows during charging and discharging.
b. __F__ More (The same) charge flows through the single bulb than through the two bulbs.
c. __T___ Charge flows at a greater flow rate through the single bulb than through the two bulbs.
d. ___T__ The single bulb shines brighter than either bulb in the two-bulb circuit.
e. __T___ The total resistance of the two bulbs is greater than that of the single bulb.
f.
g.
___T__ A compass would show a larger deflection for the left circuit than for the right.
__F___ The brightest bulb(s) indicate the fastest (greatest flow rate) charge flow.