Transcript Circuits - Camden Central Schools

Circuits
Answer Me!!!

What is required for electricity to flow?
Circuit Elements

A circuit must have




A source of potential difference (battery)
A source of resistance (resistor)
Wires connecting both terminals of the potential
difference source
A circuit may have



Switches
Multiple resistors
Voltmeters or Ammeters connected
Circuit Symbols

Be sure to check your reference tables
for appropriate symbols to use in
circuit diagrams.
Ammeters & Voltmeters

Ammeter



Measures Current
Connected in Series
Low Resistance

Voltmeter



Measures Potential Diff
Connected in Parallel
High Resistance
Types of Circuits

There are two types of circuits:


Series circuits – have only 1 path for
current to flow.
Parallel circuits – have multiple paths for
current to flow.
Series Circuits

The current flows from the battery to R1 through R2
and then through R3 then back to the battery.
Current in a Series Circuit


In a series circuit current is the same
through all parts of the circuit.
That means that the current coming
from the battery is equal to the current
through any resistor.
Itotal = I1 = I2 = I3 = …
Potential Difference in a
Series Circuit

The potential difference provided by
the battery is equal to the sum of the
potential differences across each
resistor in the circuit.
Vtotal = V1 + V2 + V3 + …

Note that potential difference for each
resistor is consistent with Ohm’s Law.
Resistance in a Series Circuit

Ohm’s Law States:
V
I
Rtotal

So,

And therefore:
Rtotal

R
Vtotal

I total
V1  V2  V3  ... V1 V2 V3

    R1  R2  R3
I total
I
I
I
Rtotal = R1 + R2 + R3 + …
Practice Problem 1

The diagram below shows resistors R1, R2
and R3 connected to a 12V battery. If the
voltage across R1 is 3V and the voltage
across R2 is 4V, what is the potential
difference across R3?
3V
4V
12 V
Practice Problem 2

R1 = 100W; R2 = 12W; and R3 = 4W in
a series circuit. Find the total
(equivalent) resistance.
Practice Problem 3

The diagram shows a circuit with two
resistors. What is the reading on the
ammeter?
Practice Problem 4

A 30 ohm and 60 ohm resistors are
connected in series to 12 V battery.
Compared to the current through the
30 ohm resistor, the current through
the 60 ohm resistor is



Smaller
Larger
The same
Practice Problem 5

Determine the reading of the
voltmeter.
Practice Problem 6

At what value must the variable
resistor be set to produce a current of
1.0 A through R1?
Practice Problem 7

What is the reading of voltmeter V1?
Practice Problem 8

A 100 ohm resistor and an unknown
resistor are connected in series to a
10V battery. If the potential drop
across the 100 ohm resistor is 4 V,
what is the resistance of the unknown
resistor?
Answer Me!!!

What makes a circuit a parallel circuit?
Parallel Circuits

Current can flow from the battery to either
R1, R2 or R3 and then back to the battery.
Current will take the path of least resistance.
Current in a Parallel Circuit

In a parallel circuit, total current equals
the sum of all the currents in the circuit
(current through each parallel path).
Itotal = I1 + I2 + I3 + …
Potential difference in Parallel
Circuits

In a parallel circuit, the potential
difference is the same in all parts of
the circuit and is also the same as the
total voltage (from the battery).
Vtotal = V1 = V2 = V3 = …
Resistance in a Parallel Circuit

Using Ohm’s law, we see:
V
Req 
I1  I 2  I 3  ...

Also stated as:
1
1 1
1
    ...
Req R1 R2 R3

Note that Req is always less than any individual
resistance in a parallel circuit.
Conservation of Charge in Electric
Circuits


Charge in an electric circuit must be
conserved.
At any junction in a circuit, the sum of
the currents entering the junction must
equal the sum of the currents leaving.
Practice Problem

The diagram below shows currents in
a segment of an electric circuit. Draw
the direction and label the magnitude
of the current through A.
8A
3A
4A
A
Practice Problem 9

What are the correct readings of the
two voltmeters?
Practice Problem 10

What is the total resistance of this
circuit segment?
Practice Problem 11

What is the total (equivalent)
resistance of the following circuit?
Practice Problem 12

Two identical resistors connected in
parallel have an equivalent resistance
of 40 ohms. What is the resistance of
each resistor?
Practice Problem 13

Resistors R1 and R2 have and
equivalent resistance of 6W when
connected in parallel. The resistance
of R1 could be:




1W
5W
8W
4W
Answer Me!!!

What is the current measured by
ammeter A?
Practice Problem 15

What is the current reading of
ammeter A?
Answer Me!!!

Draw a series circuit that has 3
resistors. Then draw a properly
connected ammeter to measure the
total current and a properly connected
voltmeter to measure the potential
drop across resistor 1.