Download Resistance and Ohm`s Law

Resistance and Ohm’s Law
Name ____________________________________________ Date _________
Opposition to the flow of charge is known as __________________. (
_________ (
). Its unit is the
). Electric charges are slowed down by ____________________ with
____________ in the wire. The resistance of a wire depends on three things, the
__________________ of which it is made, the ____________ and the _____________ of the
wire. The _______________ the wire the less resistance but the ______________ the wire the
more resistance. Higher resistance means a _____________ ________________ to the flow of
___________. The _____________ the resistance of a wire, the ________ current for a given
voltage. _______________ is a good conductor, _________ is a poor conductor.
Expressed as an equation:
R=
Where  is the resistivity of the material. Conductors have the _______________ resistivity and
______________ have the biggest resistivity.
Example: Suppose you want to connect your stereo to remote speakers. If each wire must be 20
m long and has a cross sectional area of 3.36 x 10-6 m2, what is the resistance of each wire?
(copper = 1.68 x 10-8 m). If the wire was aluminum, what would happen to the wire’s resistance?
Also the resistance of a metal ______________ with ___________________. At_____________
temperatures the atoms move around more ______________ and get in the way of flowing
electric charges. Materials that have essentially zero resistance at very low temperatures are
called ______________________. This means that almost no ______________ is wasted.
Superconductors are useful where large ______________ are required such as in
____________________ ___________________ and in motors.
Ohm’s law identifies the relationship between ________________, __________________ and
__________________.
It states that __________________________________________________________________
_____________________________________________________________________________
As an equation Ohm’s Law is:
As symbols it is:
As units it is:
Use the Ohm’s Law in the triangle to
find the quantity you want.
Cover the letter you want to determine
with your finger and the remaining two
letters show the formula that you need
to use.
V
I x R
What is the resistance of a clothes iron that draws a current of 12A from an outlet at 120 V?
If a potential difference of 6 V is across a 25  resistance (load) how much current flows through
it?
What is the potential difference across a 20  resistance (load) that draws 5.5 A from an outlet?
The current in an incandescent lamp is 0.5 A when connected to a 120 V circuit, and 0.2 A when
connected to a 10 V source. Does the resistance of the lamp change in these cases? Explain
your answer and defend it with numerical values.