Download PHYS 100 Introductory Physics Laboratory V_F02

PHYS 100
Dr. Labroo
Introductory Physics Laboratory
V_F02
Experiment 8: Charges, Currents and Simple Circuits
Objectives:
1. To investigate the nature of static electricity.
2. To build a continuity tester and classify materials as insulators or conductors.
3. To investigate the properties of series and parallel circuits.
Suggested Reading:
Pages 373 – 392 (Ch. 21) and 399 – 412 (Ch. 22) of the text.
Equipment and Supplies:
Glass rod and wool, ebony rod and fur, electrometer, some common materials, light bulbs,
wires, switch, current meter, and a current source.
Introduction:
Electric charge, like the mass, is an inherent property of matter. But unlike mass, charges can
be positive (protons) or negative (electrons). When brought close to each other, these charges exert
forces on each other. This kind of force, called the Coulomb force depends on the magnitude of the
charges and the separation distance between them. Unlike the gravitational force, which is only
attractive, the electrostatic force can be either attractive (between unlike charges) or repulsive (between
like charges).
When charges flow through an electrical conductor, they form an electric current. Insulators,
on the other hand, offer a very high resistance to the flow of charges. It takes a battery to get the
charges flowing through a circuit by creating a potential difference between the battery terminals. In a
circuit, charges always flow from a higher potential to a lower potential in pretty much the same way
as water flows from high pressure to low pressure. The amount of current flowing through a circuit
depends on the potential difference (Voltage) of the battery and the resistance of the circuit. This is
called the Ohm’s Law and it is written as follows:
Current 
Votage
Resistance
Power consumption of an electric circuit depends on the applied voltage and the total current
through the circuit.
Power = Voltage x Current
Light bulbs (resistors) can be placed in a circuit in two ways: series connection and parallel
connection. Among the many activities of this lab, you will learn how to construct a simple circuit and
then make series and parallel connections using light bulbs. You will then investigate the properties of
these circuits.
Procedure:
Part I
1. This part is set up as a demonstration by your instructor. Follow the instructions and write
down your answers in the data sheet provided.
Part II
BULB
1. Use a single light bulb from the given circuit
board and some wires, construct the circuit
as shown here. This is your continuity tester.
2. When you connect the open end the light bulb
should light up.
3. Place various materials provided to you between
the open ends of your tester and see if the bulb lights
up or not. Write down your observations in the table.
BATTERY
+
-
OPEN END
Part III
Series Circuit
Parallel Circuit
1. Using the picture shown above, construct the series circuit for the bulbs.
2. Note the current while adding bulbs to the circuit.
3. Calculate the circuit resistance and power by using the appropriate formulas. The applied
voltage is 6 Volts.
4. Make a graph of current versus number of light bulbs from your data.
5. Do the remaining things you are asked to do in the data table and write down your answers.
6. Repeat steps 1 through 5 for the parallel circuit.
Questions:
1. When you rub plastic rod on fur, the rod gets negatively charged.
a) What charge, if any, does the fur acquire?
b) What do you think would happen if the plastic rod and fur were then brought back into
contact with each other?
2. Consider your data from Part II. Do you notice anything common between conductors?
Explain your answer.
3. Compare the series circuit to a parallel circuit. In which circuit does a greater amount of
current flow? Which consumes more energy? Which circuit offers a greater resistance to the
current flow?
4. If you turn off your TV at home, it does not affect the working of other appliances. Based on
this, how do you think the appliances are wired in your home?
Report Requirements:
Brief summary of the experiment, data, and answers to the above questions.
PHYS 100 Laboratory
Data Sheet 1
Name:
Experiment 8
Partners:
Part I:
Describe what happens to the electroscope when:
A negatively charged plastic rod is touched to the metal top. Briefly explain why?
A negatively charged plastic rod is brought close to the negatively charged electroscope. Why?
A positively charged glass rod is brought close to the negatively charged electroscope. Why?
Part II:
Material
Paper
Iron
Plastic
Wax
Aluminum
Copper
Wood
Insulator or Conductor?
PHYS 100 Laboratory
Data Sheet 2
Experiment 8
Part III:
Series Circuit
Number of
Light
Bulbs
Current
(Amperes)
Circuit
Resistance
(Ohms)
Parallel Circuit
Power
(Watts)
Number of
Light
Bulbs
Current
(Amperes)
Circuit
Resistance
(Ohms)
Power
(Watts)
1. Compare the overall brightness of light bulbs in parallel and series circuit. In which circuit are the
bulbs brighter and why?
2. What happens to the brightness of the other bulbs, when you remove (unscrew) one bulb from the
circuit? In each case explain why.
Series circuit:
Parallel circuit:
3. What happens to the brightness of the other bulbs when you short circuit (see figure below) one of
them? In each case explain why.
Series circuit:
Parallel circuit:
Short circuit: Connect a wire
across the bulb, like so…