Chapter 19 DC Circuits Flashcards
Discuss the advantages and disadvantages of Christmas tree lights connected in parallel versus those connected in series.
Series: Pro • easier to make/ less complex Con • single pathway • dimmer • can't tell which bulb blew out
Parallel: Pro • multiple pathways • same voltage/ brightness Con • more wires • current still going through after bulb blow out/ high voltage & electric shock
Explain why birds can sit on power lines safely, while leaning a metal ladder up against one to fetch a stuck life is extremely dangerous.
R = Resistivity • Length / cross sectional area
V = I • R
The bird’s feet are closely spaced, allowing only a small resistance. This leads to a small potential difference. The positivity of the wire is, however, attracted to the negativity on the ground and travels through metal ladders (conductor).
Household outlets are often double outlets. Are these connected in series or parallel? How do you know?
Parallel, b/c there is no voltage drop when multiple things are plugged in. In a series circuit, something always has to be plugged in. If one thing blew out, everything blows out with it.
Explain why Kirchhoff’s first (junction) rule is equivalent to conservation of electric charge.
Kirchhoff’s rule: the amount of electrons that passes through a parallel circuit is always equal to the amount that leaves it.
The current remains constant, never gain or lost. Conservation of energy = total energy never gain or lost.
Explain why Kirchhoff’s second (loop) rule is a result of the conservation of energy.
Kirchhoff’s rule: potential released is the same that travels back through the voltage source.
W = q • V
W oc V
When energy changes there’s is work. Since there is no change in energy, there’s no work. Work is proportional to voltage, so no work = no change in voltage.
How does the overall resistance of your room’s electric circuit change when instead of having a single 60-W lightbulb on, you turn on an additional 100-W bulb?
P = V^2 / R
P oc 1 / R
The greater the power the smaller the resistance. The overall resistance of the room decreases.
Compare and discuss the formula for resistors and for capacitors when connected in series and in parallel.
Q = C • V Series Parallel Q (Tot) = Q Q (Tot) = Q + Q V (Tot) = V + V V (Tot) = V 1 / C = 1 / C + 1 / C C (Tot) = C + C V = I • R V in capacitor = resistor Q in capacitor = I in resistor C in capacitor = opposite of R in resistor
Suppose that 3 identical capacitors are connected to a battery. Will they store more energy if connected in series or in parallel?
C in parallel would store more energy than in series b/c the total C increases in parallel.
PE = 1/2CV^2
The greater the C the more energy stored assuming V is constant.
