Resistance in a wire simulation answers

PHY112/172/262 ON-LINE LAB #2 Electrical resistance and circuits

Lab #2 Electrical resistance and circuits

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Overview

This lab is composed of tasks utilizing PhET (Physics Education technology) simulations. You will be using this interactive web-based program to complete this lab.

If you have questions or problems with the interactive website, be sure to ask your TA for assistance.

Instructions:

Download and save this document to your computer. Answer the questions directly in this document. When you are done, SAVE the file as “PHYSICS LAB 2”, and return it to your TA via BB Learn. Please contact your TA with any questions or other issues.

PART I

Go to the Resistance in a wire site at:

https://phet.colorado.edu/sims/html/resistance-in-a-wire/latest/resistance-in-a-wire_en.html

The following interactive screen will appear:

Take some time exploring the relationships between the four variables: the wire’s resistance (R), the wire’s length (L), the wire’s cross-sectional area (A), and the wire’s resistivity (ρ).

QUESTIONS:

a) Write a paragraph explaining the relationships that you’ve discovered between these variables.

b) Use your own words to define the physical quality of resistivity (ρ).

c) Now, do an internet search and find out what the reciprocal quality to resistivity is.

Then answer the following questions in the box provided:

1. What is the technical term for this quality? Have you heard this term used before?

2. What is the definition of this term?

3. Using your own words, explain why you think this physical quality of electrical conductors is an essential consideration when designing circuits.

Part II

Familiarize yourself with the circuit building simulation:

Go to the Circuit Construction Kit website

http://phet.colorado.edu/en/simulation/circuit-construction-kit-dc

Click on the main icon. Once it loads, click on the “Lab” icon.

Once you access the simulation, you will want to spend some time familiarizing yourself with it so that you understand how to move wires, bulbs, batteries, resistors etc. and how the Voltmeter and Ammeter work.

When making a circuit in this simulation you will need to always have some kind of “load”, this will be either a resistor or light bulb (Fun exercise: Try making a closed circuit with just wires and a battery, and see the dramatic results)

Important Note:

· The in-line Ammeter must be connected in series, in other words you must break the circuit and place either end of the wires into the meter.

· The Voltmeter should be placed across a component.

Example:

On the left-hand side of the screen is a scrolling menu for a variety of

electrical components and other objects. Go ahead and scroll through, check them all out, and see how they work.

On the right-hand side of the screen you will find multiple control functions, including the option of using either pictures or symbols when constructing your circuits. Try out all the controls and see how they work.

One of the cool things about this simulation is that the brightness of the bulbs will change with varying conditions, such as when extra bulbs are placed in the circuit, or by increasing or decreasing voltage.

Next you should set up a “simple circuit” like the one bellow. This will be an opportunity to see how to use the simulation by rearranging components, changing the voltage, etc. Try changing voltage, wire resistance and battery resistance.

Place an Ammeter into the circuit.

Test the voltage across the battery terminals by using the Voltmeter.

You do not have to record any data yet.

Note: To disconnect a component or a wire that you’ve already put in place, simply left click on that connection and a pair of scissors will appear, click on the scissor icon to disconnect the two components.

Part III

Setting up and measuring basic circuits:

We will now set up a variety of circuits and record some data.

You may use the symbols or the pictures, whichever you prefer for building these circuits.

1. Build this simple circuit using one 9-volt battery and one light bulb.

QUESTIONS:

a) When you close the switch, what is the current reading on the Ammeter?

b) Does the voltage change?

2. Series Circuits:

Using the same circuit, add a second bulb in series .

QUESTIONS:

a) When you close the switch, what is the current reading on the Ammeter?

b) Does the voltage change across the battery?

c) What is voltage across the terminals of each of the lightbulbs?

d) What do you predict will happen to the current when you add a third bulb?

e) What do you predict will happen to the voltage across the terminals of the lightbulbs when you add a third bulb?

We will continue this process of building this series circuit by adding first a 3rd and then finally a 4th bulb.

First add the third bulb in series

f) What is the measured current when you added the 3rd bulb?

g) What is the measured voltage across each of the 3 bulbs?

Next add the fourth bulb

h) What was the measured current when you added the 4th bulb?

i) What is the measured voltage across each of the 4 bulbs?

j) Does the resistance in the series circuit increase or decrease as you add more bulbs?

k) In your own words, describe the relationship between the current in a series circuit and the amount of resistance (in this case the number of bulbs).

l) How does the voltage change as you add more bulbs?

m) Write out OHM’s Law (look it up if you need to).

Do your measurements confirm this mathematical relationship?

Parallel Circuits:

3. Next, we’ll build parallel circuits. The example below has three bubs, but first build a circuit with just two bulbs.

QUESTIONS:

a) When you close the switch on your two-bulb parallel circuit, what is the current reading on the ammeter?

b) How does this compare to the current in single bulb circuit that you built earlier?

c) Measure the voltage across the bulb terminals as you did with the series circuit.

What is the voltage for each bulb?

d) Use the “spot ammeter” to measure the current in each branch of the parallel circuit (see figure below). What are the measurements?