Aim# 1 : What is an electrical circuit?
Date______
A Simple Electrical Circuit Voltage drop
ex:________________________
 Complete path through a
___________________________
Voltage: Electrical Potential measured in Volts
Resistance: Electrical “Friction” (ohms, )
Current: charge flow per second. (Amperes, A)
V=IR
“Equivalent resistance” – the total resistance of the circuit
Series Circuits:
Voltage
Current
Resistance
2. What is the voltage
drop across the
unknown resistor?
Resistors in Parallel: Each resistor has a separate path to the power supply.
Voltage
Current
Resistance
Solving Circuit Problems
1. Three resistors 35, 15, 50, are connected in series with an ammeter, and a 200V power
supply. Calculate the voltage drop and current through each resistor.
Voltage
2.
Current
Resistance
A 100.-ohm resistor and an unknown resistor are connected in series to a 10.0-volt battery. If the
potential drop across the 100.-ohm resistor is 4.00 volts, draw the circuit and complete the grid.
Include an ammeter and a voltmeter.
R
1
2
total
Voltage
Current
Resistance
Aim 2: How do we solve mixed circuit problems? Date______
Warm up DO NOW:
Two resistors are connected in parallel to a 24V battery. The current in the first resistor is 2A, and the
equivalent resistance of the circuit is 4. Draw the circuit with ammeters and one voltmeter reading
total voltage. Complete the grid.
Voltage
Current
Resistance
Circuits wired partially in series and partially in parallel can be resolved
step by step.
3.
V
I
R
3.
4.
V
I
r
5. How much current will pass through R? What is R if the total
voltage drop across the network is 25v?
V
I
R
6.
7. Consider the circuit at right. All the bulbs have resistance R.
a.
What is the resistance of the circuit while the switch is open?
b.
What is the resistance of the circuit when the switch is closed?
c.
How does closing the switch affect the brightness of bulbs A and B?
Explain in terms of current and potential drop.
8. Find equivalent resistance
Aim #3 How is current related to power?
Date_______
Basic Definitions:
Voltage: Energy per charge
I=
V=
Current: charge per time
Power = energy/second
P=
Use Ohms law to write the power equation in terms of R and V and R and I .
V=IR I =V/R
Imagine a 100 watt and 60 Watt bulb connected in series and parallel to 120 V.
Determine the resistance, current and brightness (power) for each circuit?
144 
120 V
120 V
a. Energy Usage
b. Kilowatt Hour
i. A kilowatt-hour is a unit of __________________. 1000 watts for one hour = ________________J
1.
2. In
the circuit shown, the sizes of the resistors vary as
R3 > R1 > R2 > R4. Four students discussing the currents in this
circuit make the following statements:
Ajay: “I think the current in R1 will be the largest because all of the
current from the battery goes through it.”
T/F Explain:__________________________________________________
Belen: “Right, and after R1 the current splits into two parts at the
junction. The current through R2, R3, and R4 will all be the same because
there are two branches in the circuit and each branch will get half of the
current.”
T/F Explain:__________________________________________________
Ciara: “From Ohm’s law, current is biggest where resistance is smallest. I think the current
through R2 will be largest because that branch has the lowest resistance in the circuit.”
T/F Explain:__________________________________________________
Damaris: “Also using Ohm’s law, I think the current in R3 will be the smallest because R3 has
the largest resistance. The current in R4 will be largest, because that resistor has the smallest
resistance.”
T/F Explain:__________________________________________________
Efren: “The current in R3 will be the same as the current in R4 because they are in the same
branch.” T/F Explain:__________________________________________________
3.
Aim 4 What factors change an objects resistance?
Date_______
Factors that affect resistance are:



Dimensions:
o ________________________ increases resistance.
o __________________________ decreases resistance
The material’s atomic properties
__________________ (Hotter wires have higher resistances).
Equation:
ρ = _____________________________________units: ________________
c. Concept: As a wire is stretched out so that its length increases, its cross-sectional area decreases, while the
total volume of the wire remains constant. Will the resistance after the stretch be (1) greater than, (2) the
same as, or (3) less than that before the stretch?
d. Concept: Wire 1 has a length L and a circular cross section of diameter D. Wire 2 is constructed from the
same material as wire 1 and has the same shape, but its length is 2L, and its diameter is 2D. Is the resistance
of wire 2 (a) the same as that of wire 1, (b) twice that of wire 1 or (c) half that of wire 1?
i.
ii.
iii.
Ohmic means having a constant resistance.
e. Concept: If the voltage were plotted on the same graph versus current for two ohmic conductors with
different resistances, how could you tell which is less resistive?
f. Concept: When more current flows through the filament of a lamp its temperature increases What happens
to the resistance as the voltage increases further?_________________________ Sketch on the graph the
relation between voltage and current.
Superconductors
i. When cooled to a certain temperatures, superconductors have ______________________________.
Measuring Voltage and current: Ammeters and Voltmeters



Ammeters Measure Current
Ammeters are connected in ________________ with a circuit.
Ammeters have very ______resistance so that current flows through it without affecting the rest
of the circuit.
Voltmeters: Measure Potential Difference or Voltage

Voltmeters are connected ___________ in a circuit.

Voltmeters have a very high resistance so____________
current flows through it, leaving the circuit unaffected.
Aim 5: What are Kirchhoff’s Circuit laws?
Date________
Now try this…
This circuit cannot be
simplified
 All circuits on the AP exams can be resolved into series or parallel
segments
Kirchhoff’s Rules
Junction Rule
The total current entering a junction must __________________ the total
current leaving a junction.
1.
What is the current in R1 and R2
2. Which of the following is a correct junction rule equation for the
diagram below?
Voltage Loop Rule

Around any closed loop the sum of the potential gains = the potential drops.



Resistors dissipate energy  voltage drops
Batteries add energy so there is a voltage gain.
Voltage Gains /drops must follow the direction of
the Current (if the loop segment is against the
current negate the sign)
For Potential sources:
 Potential increases (going from ___ to ____)
across the Battery.


Potential decreases as you go from ______ to _______across a battery and also
drops voltage across the resistor.
1. Which of the following is a correct loop
rule equation for the diagram below?
2. Solve for I1,I2,I3 using any method:
V
I
VT=
Battery EMF
i. Electromotive Force (Emf), ___- The potential difference, V, across the terminals of a
battery when it not to a circuit. (The maximum potential difference).
Terminal Voltage, V
ii. Terminal voltage, V - The actual potential the battery gives the circuit.
iii. When current flows through a battery in
a circuit, resistance inside the battery
always causes the terminal voltage to be
_______________ than the emf.
iv. Usually internal resistances are so small
that the terminal voltage
________________ the emf.
R
Aim 6: What are Capacitors ?
Date________
A capacitor is a device for storing charge and energy.




Made from two parallel conducting plates with a space between them.
The plates have an equal and opposite charge Q
The amount of charge that can be stored is
defined by the “Capacitance”
Capacitance is determined by the size of the
plates, the distance between them and the
material between the plates.
How do capacitors behave in a circuit:
Charging a capacitor: flip switch to a



Immediately charges flows clockwise like a
________ with no resistance.
After some time the capacitor fills.
Eventually current will __________
Completele Charged: no current flows
Current (A)
Discharging : flip switch to b


Immediately charge flows ________________as if there was a wire with no
resistance.
Eventually capacitor is empty and current____________
Current (A)
Summarize: differences between Resistors and Capacitors:
Resistors
Capacitors
Question 55-57:
57. What happens when the switch opens again?___________________________
Aim 7: Multiple Capacitor Circuits
Date_____
Multiple capacitors
Series
parallel
1. Calculate the total capacitance, the voltage drop and the charge on each
capacitor
2.
3. Combinations of series and parallel: Use same strategy as resistance.
V
Q
C
--------------------------------------------------------------------------------------------
4. In the circuit at right: Ro is 200Ω, R1 is 100Ω, C is 5µF and R2 is
100Ω. When the switch is closed, the capacitor becomes fully charged and holds 15µC. a)
What is the battery voltage?
b) After being fully charged the switch is opened again. What happens and what current will
flow through each resistor?
Aim 8: Practical Circuits Applications
Date______
Fuse/Circuit breakers:
a safety device that shuts off current when it gets too high.
Fuse are wired in series to the main power lines. (draw the circuit)
Voltage Dividers/ Variable resistors:
Example:
When a load is applied Real Vout will
be less than prediction.
Current Dividers:
Example: What is the current in each branch?
What is the ratio of the resistors?
Current divider for
two resistors:
Shunt directs most of current away from a sensitve device
such as a galvanometer.
Multiple power suplies:
must use Kirchkoffs loop rule:
If each supply is 1.5v what is the V across the resistor?
Determine the current in each case:
5Ω
Non OHmic Resistors
Recharging Batteries
Capacitor X with a capacitance C is connected to a battery of voltage V. Capacitor Y of capacitance 2C is
connected to another battery of voltage 4V. Both capacitors are then disconnected from the batteries
and connected to each other in parallel. (a) What is the overall charge on both capacitors in terms of C
and V? (b) What is the potential difference across the capacitors? (c) Using your answers from part (b),
write an expression for the charge on each capacitor. (d) How does the energy stored in the capacitors
before they were connected in parallel compare to the energy stored after they are connected in
parallel? Justify your answer.
1.
Aim 76: How do we solve circuits with capacitors? Date________
V
I
R
VT=
1. A 100.-ohm resistor and an unknown resistor are connected in series to a 10.0-volt battery. If the
potential drop across the 100.-ohm resistor is 4.00 volts, draw the circuit and complete the grid.
Include an ammeter and a voltmeter.
R
Voltage
Current
Resistance
1
2
total
2. Fill in the grid for the following circuit:
Resistor Voltage
#
1
2
3
total
Current
Resistance
5.
V
I
r
V
I
r
V
I
r
V
I
r
6.
7.