PHYS 1415 Lab-06: Electrical measurements
Name: _____________________
Objectives:
· To learn to design and construct simple circuits using batteries, bulbs, wires, and switches.
· To understand the measurement of cu
ent and voltage.
OVERVIEW
In the following lab, you are going to discover and extend theories about electric charge and potential difference (voltage) and apply them to electric circuits. What you learn will be one of the most practical parts of the whole physics course, since electric circuits form the backbone of modern technology. Without an understanding of electric circuits, we wouldn’t have lights, air conditioners, automobiles, TV sets, telephones, computers, or photocopying machines.
A battery is a device that generates an electric potential difference (voltage) from other forms of energy. The type of batteries we typically use are known as chemical batteries because they convert internal chemical energy (energy stored in chemical bonds) into electrical energy.
As a result of a potential difference, electric charge is repelled from one terminal of the battery and attracted to the other. However, no charge can flow out of a battery unless there is a conducting material connected between its terminals. If this conductor happens to be the filament in a small light bulb, the flow of charge will cause the light bulb to glow.
We begin exploring electric cu
ent by lighting a bulb with a battery. You will be using PhET simulation Circuit Construction Kit: DC - Virtual Lab (https:
phet.colorado.edu/en/simulation/circuit-construction-kit-dc-virtual-lab)
Activity 1: A
angements that Cause a Bulb to Light
1. Find some a
angements in which the bulb lights and some in which it does not light. For instance, try the a
angement shown in figure below.
Figure 1
Question – 1: Sketch two a
angements for which the bulb lights. Upload your sketch.
Question – 2: Sketch two a
angements for which the bulb doesn’t light. Upload your sketch.
Question – 3: Describe as fully as possible the conditions needed for the bulb to light. Explain why the bulb fails to light in the a
angements drawn in answer to Question 1-2.
2. Click on “values” on the right. This will show you the values of the light bulb and battery connected in the circuit.
3. Click on the battery. You will see a voltage control slider at the bottom. Slide it and observe the
ightness of the bulb.
Question – 4: As the voltage of the battery increases,
ightness of the bulb ______________.
Activity 2: Other Materials Between the Battery and the Bul
Next you will explore materials connected between a battery and a bulb allow to light. Since it seems that something flows from the battery to the bulb, we refer to materials that allow this flow as conductors and those that don’t as nonconductors or insulators.
Set up the wires, battery, and bulb so that the bulb lights, example, one of the a
angements drawn in you answer to Question – 1. Then, stick a variety of the common objects available (like dollar bill, paper clip, eraser, etc) between the battery and the bulb.
Question – 5: List some materials that allow the bulb to light.
Question – 6: List some materials that prevent the bulb from lighting.
Question – 7: What type of materials seem to be conductors? What types seem to be nonconductors?
Activity 3: Measure Cu
ent in a Circuit
To measure the cu
ent through a part of the circuit, you must
eak open the circuit at the point where you want to measure the cu
ent and insert the cu
ent measuring device called ammeter. That is, disconnect the circuit, put in the ammeter, and reconnect with it in place. We say that the ammeter is connected in series.
Figure 2
Set up an electrical circuit as shown below. Connect an ammeter between battery and light bulb and ammeter between the light bulb and the switch.
Figure 3
Question – 8: Did you observe a significant difference in the cu
ents flowing at these two locations in the circuit, or was the cu
ent the same?
Question – 9: What is the direction of cu
ent flowing through the circuit? Is cu
ent flowing in same or opposite direction through the ammeters?
Connect the ammeter in parallel as shown in Figure 4 below. Slowly increase the power to the circuit and observe the ammeter and the bulb.
Figure 4
Question – 10: What do you observe when you close the switch?
Activity 4: Measure Voltage
To measure potential difference or voltage, you do not have to
eak the circuit. The voltage measuring device used is called voltmeter. You must connect the voltmeter leads one on each side of the circuit element. Standard practice is to touch the red lead of voltmeter to the positive terminal of the battery and the black lead to the negative terminal.
Set up an electrical circuit as shown below in Figure 5.
Figure 5
Question – 11: Connect the voltmeter across the battery. What is the voltmeter reading?
Question – 12: Connect the voltmeter across the light bulb. What is the voltmeter reading?
Question – 13: What do you observe when you swap the leads of the voltmeter across the light bulb? Did it affect the cu
ent flow?
Summing up: When the ammeter is connected co
ectly, the circuit behaves as it did when no meters were connected (increasing the power increases the
ightness of the bulb). When the power is increased, the ammeter shows increased cu
ent in the circuit. When the ammeter is connected inco
ectly, the bulb does not light all although the ammeter shows significant cu
ent.
Question – 14: The co
ect method is to connect the ammeter to the circuit in
a) Series
) Parallel
When the voltmeter is connected co
ectly, the circuit behaves as it did when no meters were connected (increasing the power increases the
ightness of the bulb). When the power is increased, the voltmeter shows increased voltage in the circuit. When the voltmeter is connected inco
ectly, the bulb does not light at all although the voltmeter shows significant voltage.
Question – 15: The co
ect method is to connect the voltmeter to the circuit in
a) Series
) Parallel
Activity 5: Ohm’s Law
Use the Ohm’s law along with measured values of V and I to calculate the resistance of the light bulb (assuming that the wires are of negligible resistance). Show all your work below.
Resistance of the light bulb: R (calculated) =
Now click on the light bulb in your circuit, the light bulb resistance will be displayed. Write it down below.
R (actual) =
Does your calculated value match with the actual value?