Transcript What are electric circuits?

Ch. 20 - Electricity
IV. Electrical Circuits & Power
(p.706-714)
 Ohms Law
 Series circuits
 Parallel circuits
 Power
Things you should already
know or be able to do…
• Construct a simple electrical circuit
using wires, batteries and light bulbs.
• Can you do this??? You need to do
this to pass this weeks test on
Electricity
Learning Target:
Describe the relationships
between current, voltage,
and resistance.
Current, Voltage & Resistance
 Electricity & Water Analogy: Pressure in a hose
(V), rate the water flows through the hose (I)
and the diameter of hose ( R) are all related.
 If you change one, it affects the others
The relationship is known as
Ohm’s Law…
Voltage = Current x Resistance
V=IxR
Ohm’s Law
Visual: Relationship between V, I and R
 http://phet.colorado.edu/sims/ohmslaw/ohms-law_en.html
Learning Target:
Use Ohm's Law to
calculate current, voltage,
and resistance using
correct units.
Ohm’s Law
E. Ohm’s Law
 Ohm’s Law
V=I×R
V: potential
difference (V)
I: current (A)
R: resistance ()
• Voltage increases when current increases.
• Voltage decreases when resistance increases.
E. Ohm’s Law
 A lightbulb with a resistance of 160  is
plugged into a 120-V outlet. What is the
current flowing through the bulb?
GIVEN:
WORK:
R = 160 
V = 120 V
I=?
I=V÷R
I = (120 V) ÷ (160 )
I = 0.75 A
V
I
R
Practice:
There is a potential difference of 12
volts across a resistor with 0.50 amps of
current in it. The resistance of the
resistor is _________.
A. 0.5 ohms
B. 6 ohms
C. 12 ohms
D. 24 ohms
Practice:
If there is a current of 6 amps flowing
through a 3 ohm resistor, what is the
potential difference in the circuit?
A. 0.5 volts
B. 2 volts
C. 9 volts
D. 18 volts
Practice:
If a circuit has a potential difference of
120 volts and a resistance of 10 ohms,
what is the current that flows through the
circuit?
A. 0.08 amps
B. 12 amps
C. 120 amps
D. 1200 amps
Practice:
A bunch of science students get together every
Friday night for a science party. Last Friday,
they watched a couple of episodes of Bill Nye
the Science Guy. They used a TV requiring
2.00 amps and a DVD player requiring 0.50
amps and they used 120V outlets.
What is the resistance of the TV?
A. 12 ohms
B. 60 ohms
C. 240 ohms
D. 1200 ohms
 NEED Ohm’s Law Worksheet
 Complete today in class
 (We’ll review in 15 minutes)
Practice:
Ohms
4
15
2
9
6
Volts
100
150
30
45
48
Amps
25
10
15
5
8
Learning Targets
Describe the difference between
a series and parallel circuit.
Contrast how voltage and
current are applied to light bulbs
in series vs. parallel circuits.
A. Circuit Components
A - battery
B - switch
C - light bulb
D - resistor
What are electric circuits?
Circuits typically contain a voltage source, a wire conductor, and
one or more devices which use the electrical energy.
What is a series circuit?
A series circuit is one which provides a single pathway for the
current to flow. If the circuit breaks, all devices using the circuit
will fail.
What is a parallel circuit?
A parallel circuit has multiple pathways for the current to flow. If
the circuit is broken the current may pass through other
pathways and other devices will continue to work.
What is the difference between an open circuit and a closed
circuit?
A closed circuit is one in which the pathway of the electrical current is
complete and unbroken.
An open circuit is one in which the pathway of the electrical current is
broken. A switch is a device in the circuit in which the circuit can be closed
(turned on) or open (turned off).
B. Series Circuits
 Series Circuit
 current travels in a single path
• one break stops the flow of current
 current is the same throughout circuit
• lights are equal brightness
 each device receives a fraction of the total
voltage
• get dimmer as lights are added
C. Parallel Circuits
 Parallel Circuits
 current travels in multiple paths
• one break doesn’t stop flow
 current varies in different branches
• takes path of least resistance
• “bigger” light would be dimmer
 each device receives the total voltage
• no change when lights are added
A. Electrical Power
 Electrical Power
 rate at which electrical energy is
converted to another form of energy
P: power (W)
P=I×V
I: current (A)
V: potential
difference (V)
A. Electrical Power
 A calculator has a 0.01-A current flowing through it.
It operates with a potential difference of 9 V. How
much power does it use?
GIVEN:
WORK:
I = 0.01 A
V=9V
P=?
P=I·V
P = (0.01 A) (9 V)
P = 0.09 W
P
I
V
D. Household Circuits
 Combination of parallel circuits
 too many devices can cause wires to
overheat
 Safety Features:
 fuse - metal melts, breaking circuit
 circuit breaker - bimetallic strip bends
when hot, breaking circuit
Assignment
 Read pages 706 – 714
 Complete the Electrical Circuits and
Power Review Handout
 Due Thursday 6/12