# Name(s) Hr. ___ • What happens to the total (equivalent) resistance ```Name(s) _____________________________ Hr. ___
Physics: Resistors in a series connection (Using PHET). Watch movie while you
do the PHET activity
 What happens to the total (equivalent) resistance
(Req)?
 What happens to the current (I) as read by an
ammeter?
 What are voltage drops?
 Add up the voltage drops. What do they equal?
Open up the phet simulation:
1. Circuit 1: Build your basic one resistor circuit (Use 2 batteries,
each 1.5 V, one light bulb with a resistance of 10 Ohms.
a. Determine your voltage drop (voltage around the
resistor) _______________ volts
b. The voltage drop is equal to what voltage
________________
c. Determine the current with an ammeter placed in series. _______________ amps
Using PHET to examine series circuit, p. 1
2. Circuit 2: Build a two resistor circuit with two light bulbs in series. Again, 2 batteries, each 1.5V,
two light bulbs each with a resistance of 10 Ohm. Put in an ammeter to measure the current and
now we will use a voltmeter to measure the voltage drop around each light bulb and around
both light bulbs.
a)
b)
c)
d)
e)
f)
What happened to the current?
Explain why in terms of resistance or friction
What was the total voltage drop = to?
What was the voltage drop of each light bulb?
What happens to the resistance or friction in the circuit as we add this second light bulb in
series?
g) Use Ohm’s Law (V = IR) to find the Req or the equivalent or total resistance in the circuit. V =
the voltage of the light bulbs, I is the current of the ammeter. Solve for R = Req.
Using PHET to examine series circuit, p. 2
3. Circuit 3: Build a four resistor circuit with four light bulbs in series. Again, 2 batteries, each 1.5V,
four light bulbs each with a resistance of 10 Ohm. Put in an ammeter to measure the current and
now we will use a voltmeter to measure the voltage drop around each light bulb and around all
four of the light bulbs.
a)
b)
c)
d)
e)
f)
What happened to the current?
Explain why in terms of resistance or friction
What was the total voltage drop = to?
What was the voltage drop of each light bulb?
What happens to the resistance or friction in the circuit as we now have four light bulbs in
series?
g) What is the total or equivalent resistance (Req)?
Using PHET to examine series circuit, p. 3
4. Circuit 4: Now answer the questions below and then build the circuit to test your results. (Again,
2 batteries, each 1.5V, six light bulbs each with a resistance of 10 Ohms. Put in an ammeter to
measure the current and now we will use a voltmeter to measure the voltage drop around each
light bulb and around all six of the light bulbs.)
a. What happened to the current?
b. Explain why in terms of resistance or friction
c. What was the ammeter reading?
d. What was the total voltage drop = to?
e. What was the voltage drop of each light bulb?
f. What happens to the resistance or friction in the circuit as we go from four to six light
bulb in series?
g. Find the Req or the equivalent or total resistance in the circuit.
5. Circuit 5: Two non-equal
resistances (2 batteries, each
1.5V, two light bulbs one with a
resistance of 10 Ohms and one
with a resistance of 5 Ohms. Put
in an ammeter to measure the
current and now we will use a
voltmeter to measure the voltage
drop around each light bulb and
around both of the light bulbs.)
a) What was the current reported
by the ammeter?
b) What was your total resistance?
c) What is your total voltage drop?
d) What are your voltage drops across each of the light bulbs?
Using PHET to examine series circuit, p. 4
Circuit 1: One light bulb
a. Determine your voltage drop (voltage around the resistor) = 3V
b. The voltage drop is equal to what voltage: voltage of the batteries = 3V
c. Determine the current with an ammeter placed in series: 0.3Amps. The current can be
determined mathematically with Ohm’s Law: V = IR: 3V = I (10 Ω), solve for I: I = 0.3 amps.
Circuit 2: Two light bulbs in series
a) What happened to the current? (The current drops)
b) Explain why in terms of resistance or friction (The amount of current delivered to the circuit is
inversely proportional to the total resistance or friction. Since we now have 20 Ohms of
resistance, this is twice the resistance as with one light bulb and our current drops in half.)
c) What was the ammeter reading? (0.15 amps)
d) What was the total voltage drop = to? (3 Volts)
e) What was the voltage drop of each light bulb? (1.5 V)
f) What happens to the resistance or friction in the circuit as we add this second light bulb in
series? (increases)
g) Use Ohm’s Law (V = IR) to find the Req or the equivalent or total resistance in the circuit. V =
the voltage of the light bulbs, I is the current of the ammeter. Solve for R = Req. (V = I∙Req):
3V = 0.15 amps∙Req: Req = 3/0.15 = 20 Ohms. This is twice the resistance of the first circuit
with only one light bulb).
Circuit 3: Four light bulbs in series
a) What happened to the current? (Again, it drops)
b) Explain why in terms of resistance or friction (Same idea as before. We have added more
resistance to the circuit. Because of this the current decreases)
c) What was the ammeter reading? (answer: I as reported by the ammeter = 0.07 Amps. It
theoretically is &frac14; of what we had in the first circuit= 0.075 Amps but the ammeter doesn’t
show that last digit.
d) What was the total voltage drop = to? (Again 3Volts = batteries’ total voltage)
e) What was the voltage drop of each light bulb? (Each has a voltage drop = 0.75 V, this is equal
to 3 Volts / 4 light bulbs)
f) What happens to the resistance or friction in the circuit as we now have four light bulb in
series?
g) What is the total or equivalent resistance (Req)? (10 Ω + 10 Ω + 10 Ω+ 10 Ω = 40 Ω total)
Using PHET to examine series circuit, p. 5
Circuit 4: Six light bulbs in series
a.
b.
c.
d.
e.
f.
What happened to the current? (The current is now even smaller)
Explain why in terms of resistance or friction (Lots of resistance, not much current)
What was the total voltage drop = to? (answer = 3 Volts = batteries’ total voltage)
What was the voltage drop of each light bulb? (3 V/6 light bulbs = 0.5 Volts)
What happens to the resistance or friction in the circuit when we go from four to six light
bulb in series?
g. Find the Req or the equivalent or total resistance in the circuit. (answer Req = 60 Ohms)
Circuit 5: Two light bulbs with different resistances:
a)
b)
c)
d)
What was the current reported by the ammeter? (0.2 Amps)
What was your total resistance (answer should be 10 Ohms + 5 Ohms = 15 Ohms)
What is your total voltage drop? (answer should = 3V same as batteries)
What are your voltage drops across each of the light bulbs? (answers: the 10 Ohm light bulbs has
a higher resistance; it has a voltage drop of 2V. The 5 Ohm light bulb has a lower resistance and
has a smaller voltage drop of 1V. These two voltage drops still add up = 3 volts which is what was
provided by the batteries.
Using PHET to examine series circuit, p. 6
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