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REGENTS PHYSICS
STUDENT NOTES-ELECTRICITY AND MAGNETISM
ELECTRICAL CURRENT AND RESISTANCE
What is Electrical Current?
Electric Current flows through an ELECTRIC _________________ .
Parts of an Electric Circuit:
SwitchCellBatteryVoltmeterAmmeter-
Direction of “Conventional Current” in a circuit.
Two things that are necessary for electrons to flow (to have a current).
1.
2.
Conductors vs Insulators
What is Current measured in?
I=q
t
One Ampere is when 1 Coulumb of charge flows for 1 second.
What device do we use to measure current?
RESISTANCE AND OHM’S LAW
Electricity flows very well through _______________ such as copper wire. We say that the
electricity meets very little _______________________ .
Electricity does not flow very well through plastic. It has a very HIGH ___________________ .
Resistance is measured using the following equation. This equation is called _______________
LAW.
R=V
I
Reference Tables
V is for Potential Difference (Volts)
I is for Current (Amperes)
R is for Resistance (Ohms)
An Ohm is equal to
One Volt per Ampere
We use RESISTORS in wires to limit the amount of current through a wire. A FUSE is a form of
resistor.
EXAMPLE 1: A student measures a current of 0.10 ampere flowing through a lamp connected
by short wires to a 12.0 Volt source. What is the resistance of the lamp?
EXAMPLE 2: A resistor was held at constant temperature in an operating electric circuit. A
student measured the current through the resistor and the potential difference across it. The
measurements are shown in the data table below.
CURRENT (A)
POTENTIAL DIFFERENCE (V)
0.010
2.3
0.020
5.2
0.030
7.4
0.040
9.9
0.050
12.7
(a) Using the information in the data table, construct a graph on some graph paper. Current
should be on the x-axis. Draw a line of best fit through the average of the data points.
(b) Determine the slope of this line.
(c) What physical quantity does the slope represent?
FACTORS THAT AFFECT THE RESISTANCE OF A CONDUCTOR
The following factors will INCREASE the RESISTANCE of a wire…

INCREASING THE LENGTH OF THE WIRE

DECREASING THE THICKNESS OF THE WIRE

THE COMPOSITION OF THE WIRE

INCREASING THE TEMPERATURE OF THE WIRE
-The combination of the COMPOSITION and the TEMPERATURE of the wire is called
the wires ___________________ .
-Look at your Reference Tables at the chart that lists the RESISTIVITIES of several
metals at 20 degrees Celsius.
-Combining all of the above factors leads to an equation for the resistance of a
wire.
R=
p is the resistivity of the wire
L is the length of the wire
A is the cross sectional area of the wire
R is the Resistance in Ohms.
EXAMPLE: Determine the resistance of a 4.0 meter length of copper wire having a
diameter of 2.0 millimeters. Assume a temperature of 20 degrees Celsius.