SUMMARY EXERCISE
1. A circuit containing three identical bulbs in series will have equal flow rates through all
bulbs when the steady state is reached. Will it have equal flow rates through each bulb in
the transient stage at the instant the connection is made? Explain.
No. At the first instant of connection, there is no pressure difference
established across the middle bulb (yellow to yellow). Visually it appears to
light at the same time as the other two bulbs, but adding a parallel capacitor
across the middle bulb will demonstrate that the pressure difference must
build up during the transient process as charge flows through the other two
bulbs.
2. A single long bulb is connected to a fresh battery. When a second long bulb is added in
parallel to the first bulb, there is an (Increase, Decrease, or No Change) in:
a) the electric pressure difference across the battery terminals
________
b) the electric pressure difference across the first bulb
________
c) the flow rate of charge through the battery
________
d) the flow rate of charge through the first bulb
________
a) No Change ; b) No Change; c) Increase; d) No Change
3. Is the net resistance (or total resistance) of a series combination more than the resistance
of any single bulb in the combination? Why or why not?
YES. Adding more resistors in the same path will reduce each resistor’s
fraction of the total pressure difference – and reduce the flow rate and the
brightness of the bulbs in the series combination.
4.. Is the net resistance of a parallel combination more than the resistance of any single
resistor in the combination? Why or why not?
NO. Adding more resistors in parallel paths will increase the flow rate
through the combination with the same pressure difference. If the same
pressure difference is able to produce a greater flow rate, there must be less
net resistance.
5. How does the flow rate of charge in a parallel circuit divide –
a) if all branches of the circuit have the same resistance?
b) if different branches have different resistance values?
PASCO scientific
Teachers Resource Guide
T-192
a) Flow rate is equal in all branches that have the same resistance.
b) For the branches with different resistance values, a greater fraction of the
incoming flow rate goes to a branch with lower resistance.
6. Does Choice A or Choice B provide the best representation of the transient process that
occurs after the circuit is closed? Explain your reasoning.
Choose One
R
R
R
R
L
L
L
L
First Instant
of Closure
Choice A
Choice B
Steady State
Choice A. This shows unequal flow rates through the series bulbs, which
results in compression of charge in the middle wire, which increases the
pressure in that wire to a value that eventually becomes high enough so that
the flow rates are equal in the round and long bulbs. Color-coding the
diagrams would have the middle wire yellow in the First Instant circuit, and
orange in the Steady State circuit.
7. A simple circuit contains a battery and a single light bulb. What effect does adding a
wire in parallel with the light bulb have on –
a) the electric pressure difference across the bulb?
b) the flow rate of charge through the bulb?
c) the pressure difference across the battery terminals?
a) The parallel wire reduces pressure difference across the bulb to zero, acting
as a shorting wire.
b) The flow rate through the bulb becomes zero. All moving charge now
flows around it — through the shorting wire.
c) The pressure difference across the battery terminals will be reduced.
PASCO scientific
Teachers Resource Guide
T-193