Download Electricity 4

2016-17 Electricity 4
1.
Voltage (V), Current (I), or Resistance (R).
A. ____Measured in Ω.
B. ____Measured in A.
C. ____Measured in V.
D. ___From a battery.
E. ___Flows in a circuit.
F. ___Like a water pump.
2.
G.
H.
I.
J.
K.
L.
____Like water flowing.
____Reduces current.
____Pushes electricity.
____4 amps
____12 Ω
____9 V
Current
(in amps [A])
V
I=
R
Voltage
(in volts [V])
Resistance
(in ohms [Ω])
Current equals the voltage
divided by the resistance.
Voltage (V), Current (I), or Resistance (R)?
A _____
B. _____
C. _____
D. _____
If you increase resistance what decreases?
If you increases voltage what increases?
If the current decreased what increased?
If current increased what increased?
E. ____
F. _____
G. _____
H. ____
??
35 mA
9v
M1
M2
10 v
8v
3.
If current increased what decreased?
If resistance is decreased, what increases?
More batteries will increase these two quantities.
More light bulbs will increase this.
The diagram at the left is from our lab in class.
A. Which meter or meters is an ammeter
(measuring current)?
B. Which meter or meters is a voltmeter
(measuring voltage)?
C. Which meter or meters is an ohmmeter?
D. Find three mistakes with the voltage around
the circuit. Be sure to explain why.
1.
78 mA
5v
??
2.
6v
2v
3.
M3
??
4.
10 Ω
E. Find one mistake with the current in the circuit.
Be sure to explain why.
Use the circuit at the left to answer the following.
A. Imagining that the wires are like pipes for water,
how many paths are there for the electricity to flow?
B. How much current is flowing thru the 6Ω resistor?
C. How much current is flowing thru the 8Ω resistor?
9V
0.5A
3V
6Ω
0.5A
6Ω
D. How much current is flowing thru the 9v battery?
E. What is the total resistance of the circuit?
F.
8Ω
What is the total voltage of the circuit?
G. Look at the close up of the 6Ω resistor.
i. How much current is flowing through it?
ii. Using V = IR for the 6Ω resistor, how
much voltage does it use?
The 3V battery is then removed, leaving only the 9V battery.
H. How would the total voltage change?
I.
How would the total resistance change?
J.
How would the current change?
K. Calculate the new current.
cstephenmurray.com
Copyright © 2017, C. Stephen Murray
2016-17 Electricity 4—p2
The easiest way of doing circuit problems is to “work the circuit” first, then answer the questions. “Working the circuit”
means figuring out information on the diagram and THEN answer the given questions. BIG HINT: There are going to be a lot
of numbers on the circuit when you are done. You will NOT be able to make sense of the diagram if you don’t include units.
5.
C
Part I: Working the circuit.
E
D
Use the circuit at the left to answer the following questions.
A. Calculate the total voltage of the circuit. Write it
between the batteries (there is a spot for it). Be sure
to include units.
R1 = 1Ω
F
9V
Rt =
Vt =
B. Calculate the total resistance of the circuit. Label in
the very center of the circuit (again, with units).
R2 =
3Ω
B
I=
15 V
C. Calculate the current of the circuit. Label it in the
center of the circuit. (And there’s a reason I called
it the “current” and not “total current”)
D. Since there is only one path in the circuit this current must the current flowing through each resistor,
so put arrows above each resistor and label them
with the current you already calculated.
G
R4 = 4Ω
A
VA =
I
E. Use V = IR for each resistor to calculate the voltage
used by each resistor. Label each voltage above the
resistor and make them negative to show that the
resistor USES voltage.
H
F.
Voltage
(in volts [V])
G. Now that you have the positive voltages of the batteries and the negative voltages of the resistors, add
and subtract voltages around the circuit. Label each
point with the voltages at that point.
P = VI
Power
(in watts [W])
Starting at point A in the circuit, label it 0V.
Current
(in amps [A])
This is a completed “worked circuit”. With it you
can answer any question asked.
6.
V1 = −3V
A. Add up all of the voltages used by the resistors.
3A
24V
24V
E 21V
D
B. How does the voltage used by the resistors compare
with the voltage produced by the batteries?
C
R1 = 1Ω
F 21V
9V
Vt =
24V
Rt = 8Ω
15V
B
I = 3A
R2 =
3Ω
3A
V3 =
−9V
This is always true around a closed loop.
C. How much voltage is lost from C to D?
D. Why?
E. How much current is flowing thru the 3Ω resistor?
15 V
0V
At the left is the completed “worked circuit”.
Use it to answer the following questions.
A
0V I
R4 = 4Ω
3A
V3 = −12V
cstephenmurray.com
G
12V
H 12V
F.
How much voltage is used by the 3Ω resistor?
G. Using the power equation above, how much power
is used by the 3Ω resistor?
H. Using the total voltage and current, how much
power is used by the entire circuit?
Copyright © 2017, C. Stephen Murray
cstephenmurray.com
Copyright © 2017, C. Stephen Murray
cstephenmurray.com
Copyright © 2017, C. Stephen Murray