Transcript File - MRS. PILIPCHUK

Controlling the Flow of
Electrical Current
Section 2.1-Day #2
Homework

Check and Reflect #5 and 7 (p. 303).
5. Conductivity is related a substance’s
atomic structure. Conductors allow
electrons to flow, while insulators do not
allow electrons to flow freely.
7. Metal A provides more resistance to
current flow.
The Plan

Discussion on resistance, demo, animation,
video clips, and discussion on switches and
variable resistors.

I can identify electrical conductors and
insulators and compare the resistance of
different materials.

I can identify and explain resistors and
switches.

Engineers need to know how well
different materials conduct electricity so
they can design both safe and effective
devices.
A superconductor walks into a store, the
store clerk says , “Hey get out, we don’t
serve your kind here!”
The superconductor leaves without
resistance.
Resistance

Resistance is how much current a
material will block.
Low resistance = lots of current through
(little stopped).
High resistance = little current through
(most is stopped).
How Does the Length and Width of
a Wire Relate to Resistance?
http://nuweb.neu.edu/bmaheswaran/phyu121/data/ch05/fig/fig0514.htm
Resistor

A resistor allows electrons to flow
through it, but provides resistance to it
(slows them down or restricts the flow of
electricity).

Resistance is measured in Ohms.

ohms =  resistance.
Resistors

The volume control on a stereo is a
special kind of resistor called a variable
resistor or rheostat.

A resistor is a device having resistance to
the passage of electrical current, often
used to control current in a circuit.
Is Resistance Good or Bad?

Usually the electrical energy is converted
to heat so resistors work at high
temperatures.
 (E.g., light bulbs-the filament is a resistor,
so is the burner on your stove).
Examples of Devices that Use
Resistors
Resistors

Solutions can also be resistors.
What type of water would
provide the most resistance?
1. Distilled water
2. Tap water
3. Sugar water

Resistors

Solutions can also be resistors.
What type of water would
provide the most resistance?
1. Distilled water
2. Tap water
3. Sugar water

Polygraph (Lie Detector)
http://www.polygraphsingapore.com/
Switch

The basic switch works by
maintaining or breaking
the circuit.

ON- resistor relays the
electrons (complete
circuit). Can say it is a
closed circuit.

OFF- resistor stops the
electrons (broken circuit).
Can say it opens a circuit.
Variable Resistor (Rheostat)

A variable resistor is a resistor whose
resistance can be changed by adjusting
current flow.

Rheostats can increase or decrease the
amount of current in a circuit by adjusting
the portion of the resistor that the
current travels through.
Variable Resistor (Rheostat)

The longer a current passes through a
resistor (like a nichrome wire), the more
energy is absorbed, and the less gets
through to the load.
Example
Chart
Homework

Check and Reflect #3, 8, and 9 (p. 303)
3. When a switch is off, conductors are
separated to prevent current flow. When a
switch is on, conductors are pressed
together to allow current to pass.
Homework
8. Technically, your friend is correct, pure
water does not conduct electricity.
However, it is very likely that the tap water
that has flooded the basement has
dissolved ions in it, allowing it to conduct
electricity. This would make using the
electric drill very dangerous in the flooded
basement, with a significant risk of
electrocution.
Homework
9. This would be a perfect application for a
variable resistor (rheostat). Using one
would allow you to control the amount of
current flowing to the pump, thereby
controlling how hard the pump sprays
water.