Download Unit 4 - Section 13.8 2011 Relating V to I

Grade 9 Academic Science – Unit 4 Electricity
Laboratory - Relationship between Current and Potential Difference
Section 13.8 Page 567
Stuff we know….








All materials are made up from atoms, AND all atoms consist of subatomic particles:
protons, neutrons and electrons.
Protons have a positive electrical charge, neutrons have no electrical charge while
electrons have a negative electrical charge.
Atoms are held together by powerful forces of attraction existing between the atoms
nucleus and the electrons in its outer shell.
If we separate the electrons from the nucleus, the electrons exert a potential of attraction
called a POTENTIAL DIFFERENCE (…wow…now I get that one…)
The basic electrical circuit consists of three separate but very much related quantities:
Voltage (V), Current (I) and Resistance (Ω).
If we create a circuit for the electrons to move back to the
attraction of the protons (RECALL: Law of Electric
Charges whereby opposite charges attract), the flow of
electrons is called a CURRENT. Current is the movement
or flow of electrical charge, and current is measured in
amperes or amps (A). Electrons typically flow from the
negative to the positive in a circuit (see diagram). An
amp is the number of electrons passing a certain point in
the circuit in one second. NOTE: Current can be expressed
in milli-amps (mA = 10-3A). Current that flows in a single direction is called Direct Current
(DC) and current that alternates back and forth through the circuit is known as Alternating
Current (AC).
If the electrons do not flow freely through the circuit, the restriction to this flow is called
RESISTANCE.
VOLTAGE is like the force that pushes electrons. If voltage is increased, it has a greater
ability to "push" the electrons through a given circuit. the greater the voltage, the greater
is the pressure (or pushing force) and the greater is the capacity to do work. The
difference in voltage between any two spots in a circuit is known as the Voltage Drop.
Relationship between Voltage and Current in a Circuit of Constant Resistance
The illustration shows an electrical circuit. The
Voltmeter is connected in a parallel circuit to
the load (i.e., circuit resistance (R)). This
connection is called “across the load” and
it is measuring the drop in voltage across
the load (i.e., How much energy is used up to
run the resistor). The Ammeter is connected in
series with the circuit. It is measuring the current
the line
The graph shows the linear relationship between Voltage (V)
and Current (I). NOTE: The graph would be very
different if resistance changed. IN YOUR OWN
WORDS, describe the relationship between the two
factors. In other words, how does voltage change as
current changes? …and visa versa, how does flow (i.e.,
current change when there is a change in push (i.e., voltage)?
in
From our houses, we know that some machines (e.g., stoves and clothes dryers) require more
potential difference that some other machines (e.g., night lights, battery rechargers).
 What effect does a higher potential have on current flowing through the wires of each
machine?
Purpose
 To determine the relationship between the current and the potential difference
 What is your hypothesis? In other words, what do you predict will happen in the
experiment?
Materials
 Alligator clip wires
 Voltmeter
 Ammeter
 Power supply
 Circuit (light) board
 One light (resistor or load)
 Graph Paper
 Switch (optional)
Methods
 Construct a table to record your observations. Make it logical and practical. Make sure
you collect sufficient data to answer your question(s).
 Draw a circuit diagrams to connect the light to the power supply, AND properly connects
the ammeter in series to the circuit and the voltmeter in parallel to the load
 Build the circuit using with one light, a voltmeter and an ammeter
 Turn on the power supply to a LOW SETTING
 Record the amps and the volts in your data table
 INCREASE the power setting to 25% maximum
 Record the amps and the volts in your data table
 INCREASE the power setting to 50% maximum
 Record the amps and the volts in your data table
 INCREASE the power setting to 75% maximum
 Record the amps and the volts in your data table
 INCREASE the power setting to 100% maximum
 Record the amps and the volts in your data table
 On graph paper, plot the relationship between potential difference and current. HINT:
Put potential difference on the y-axis and current on the x-axis. Looking at the date, draw
a LINE OF BEST FIT.
 Calculate the slope of the line. The formula is SLOPE = RISE / RUN
 Answer Questions 6(e) and 6(g) on Page 567 of your textbook.