Question Description

I need help with a Physics question. All explanations and answers will be used to help me learn.

This is an online lab using website simulations. Do some simple simulations and answer questions accordingly. The attached file contains all the information on the lab. No need for a lab report or anything.

This lab uses the Balloons and Static ElectricityJohn Travoltage and Charges and Fields Remote lab simulation.

 Charges and Fields
Introduction to Static Electricity

Electricity and Light

Unit 1

TA name:                                                                                            Due Date:

Student Name:

Student ID:

This lab uses the Balloons and Static Electricity  John Travoltage and Charges and Fields Remote lab simulation from PhET Interactive Simulations at University of Colorado Boulder, under the CC-BY 4.0 license.

Learning Goals: Students will be able to

  1. Describe and draw models for common static electricity concepts. (transfer of charge, induction, attraction, repulsion, and grounding)
  1. Determine the variables that affect how charged bodies interact
  2. Predict how charged bodies will interact
  3. Describe the strength and direction of the electric field around a charged body
  4. Use free-body diagrams and vector addition to help explain the interactions
  5. Compare electric fields to gravitational fields

Theory:

An Electric Field is a region in space in which electric forces act on electric charges. The Electric Field strength for any point in space is defined as the net Electric (Coulomb) Force per unit of positive charge acting on a charge placed at that point, i.e.,

                                                                                                                                    [1]

The SI unit for electric field is Newton / coulomb (N/C), or (more practically) volt/meter, (V/m).  The direction of an electric field at any point is defined as the direction of the net electric force on a positive charge placed at that point. Since, F = k q1q2/r2 (Coulomb’s Law), the Electric Field can be written in the form E = kq/r2 where r is the distance from the charge.

Faraday introduced the concept of lines of force to aid in visualizing the magnitude and direction of the total electric field about a charge or collection of charges.  These concepts are listed below.

1.  A line of force is everywhere tangent to the electric field direction.

2.  The lines of force originate on positive charges and terminate on negative charges.

3   The density of the lines of force (i.e. the lines/cm or lines/cm2) in a region of space is used to represent the electric field strength in that region of space.

4   Lines of force will not cross over or touch one another.

Electric fields can be represented by a scaled drawing, by first choosing a scale factor (proportionality factor) so that n number of lines/cm2 represent a certain value of field strength (volts/m).

                                                                                    (b)

(a)                                             

       
   
 
 

                                                            Figure 1

Examine the figure above.  The two figures represent an electric field departing a charged sphere. If we let figure 1(a) represent an electric field with field strength of E, figure 1(b) would represent an electric field with field strength of 2E. (Twice the numbers of field lines depart the charge).

In this experiment, we may estimate the electric field at certain points from the potential gradient, at these points

                                                  E = DV/Dx = (V2 – V1) / (x2 – x1)                                          [2]

Where V1 and V2 are the potential of two adjacent equipotential lines and (x2 – x1) is the distance between the lines in meters.

It is possible to find any number of points in an electric field, all of which are at the same potential (voltage). If a line or surface is constructed such that it includes all such points with equal potential, the line or surface is known as an equipotential line or surface

An expenditure of work is required when moving a charge parallel to the direction of the electric field.  To move between one equipotential line to another, an amount of work is required to satisfy the laws of conservation of energy. 

From mechanics it is known that W = Fd.  From equation [1] it can be found that F = qE.  Therefore the work to move a charge can be determined by combining the two equations to obtain W = qEd.

However, when a charged is moved along an equipotential line or surface, it is moving in a direction perpendicular to the electric field and therefore no expenditure of work is needed to move the charge.

This pre-lab is worth 5 points.

            This pre-lab is worth 5 points.

  1. What is an electric field?
  • What are the units for an electric field? List both of them.
  • What is an equipotential line?
  • Lines of force originate on ________________ charges and terminate on ________________charges.
  • Electric field lines are (parallel, perpendicular) to the equipotential lines.

Static Charges

  1. Open Balloons and Static Electricity, then explore to develop your own ideas about electrical charge.  

Describe several of your experiments and your observation with captured images from the simulation.

  1. …
  2. …
  3. …

2. Open John Travoltage , then explore to develop your own ideas about electrical charge.  

Describe several of your experiments and your observation with captured images from the simulation.

  1. …
  2. …
  3. …

Test your understanding: Without using the simulations, predict the answers to these questions, then use the simulation to check your ideas. 

Question 1. When the balloon is rubbed on the sweater, what might happen?

What do you predict for the answer?

à

Describe an experiment and include images from the simulation that supports your answer.

Question 2. What do you think will happen when the balloon is moved closer to the wall?

A picture containing drawing, light Description automatically generated

 

What do you predict for the answer?

à

Describe an experiment and include images from the simulation that supports your answer.

Question 3. What do you think the balloons will do?

 

What do you predict for the answer?

à

Describe an experiment and include images from the simulation that supports your answer.

Question 4. What might happen to the charge on the man when he touches the doorknob?

What do you predict for the answer?

à

Describe an experiment and include images from the simulation that supports your answer.

Electric Charge/Field

1. Two balloons were rubbed on a sweater like in the Balloons and Static Electricity and then hung like in the picture below. Explain why you think they move apart and what might affect how far apart they will be.

Explain your understanding:

2. Watch the short video demonstration of Electric Field Hockey .

  1. Why can you make a goal without hitting the puck?

à

  1. Why can you use either a positive charge or a negative charge to move the positively charged puck?

à

  1. What do you think would happen if you use 2 charges instead of one to make the puck move?

à

3. Examine the image with a positive and a negative charge on the playing field with the positive puck.

  1. What do you think the arrows on the puck are illustrating?

à

  1. How does the arrow from the positive charge compare and contrast to the one from the negative charge?

à

  1. Which way do you think the puck will move?

à

  1. How would the arrows look if the puck was negative?
    à

4. Open Charges and Fields.  In this simulation, a little different model is used. The little yellow “E field sensors” are like the hockey puck but they are on a high friction surface, so they stay in place allowing for measurements. Collect data by turning on Values & drag in the Tape Measure like in this image:

  1. Investigate to check your answers from #2 and #3. Write how the results of your investigation support or change your ideas.

à

  1. Determinethe relationship between distance and the strength of the electric field around a charged body.

A picture containing red, white, light, tiled Description automatically generatedTurn on Grid and Values by clicking the box with a check mark. Uncheck Electric Field. Notice the scale is 0.5 meters for one big box. Place a positive charge at a point on the grid so that it crosses a big horizontal and big vertical line.

Now drag the voltmeter to the charge, measure the potential at its center and record that value in Table 1. *Note: the voltmeter is very sensitive. You should get over 1000 volts at the center.

Complete Data Table 1 by measuring the potential at each value indicated. Plot the electric field as a function of distance using Excel. Give the plot a title and axis labels. Don’t forget units on the axis! Copy and paste the graph below Data Table 1. Adjust the size of graph so it fits nicely in the page. 

Question: Does your graph agree with the equation for an electric field? Why or why not?

Data Table 1
Potential at center of charge:
Distance (m) Potential (V) Potential Difference ΔV (V) Electric Field -ΔV/D (V/m)
0.1      
0.2      
0.3      
0.4      
0.5      
1.0      
1.5      
2.0      
2.5      
  • Determinethe relationship between amount of charge and the strength of the electric field around a charged body.

Place a positive charge on the crosshairs of the grid as you did in part b. Measure the potential and record the value as V1 for 1 +e charge in Data Table 2. Now measure the potential 1 meter from the test charge and record the value as V2. Complete Data Table 2 by measuring each value indicated. *Note: stack charges on top of each other aligning as best as possible. Plot the electric field as a function of charge number in Excel. Be sure to include a title, axis labels and units!  Copy and paste your plot below data table 2.

Question: Does your graph agree with the equation for an electric field? Why or why not?

Data Table 2

Charge (+e) 1 2 3 4 5
V1          
V2          
ΔV          
E-Field -ΔV/D          

5. Explain how electric fields are like gravitation fields and how they differ. The Electric field may be helpful.

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