Lab: Positive Particle Moves Parallel to the Electric Field

This lab consists of four parts. In Part A, you will examine the motion of a positively charged particle when it initially moves parallel to the electric field.  In Part B you will examine the motion of a positively charged particle when it initially moves perpendicularly to the electric field.  In Part C you will examine how a negatively charged particle will move when it starts perpendicular to the electric field.  Finally, in Part D you will try to get the particle to move with uniform motion.

 

Purpose - Part B

 

In this part of the lab activity you will use a computer simulation to collect data enabling you to answer the following questions:

  •  How does a positive particle move when the direction of its initial velocity is perpendicular to the direction of the electric field?

  • How can this motion be explained using physics principles?

Procedure

 

Step 1: Open the Particle in an Electric Field simulation, and enter the following settings:

  • Reset the simulation.

  • Enter a value of 75 V/m for the magnitude of the electric field in the electric field display panel and set the direction of the electric field to 270 o. 

  • Enter a value of 150 m/s for the magnitude of the initial velocity in the velocity display panel and set the direction of the initial velocity to 0 o. 

  • Set the particle's charge and mass to +2.0 C and 3.0 kg, respectively.

  • Drag the particle to a position on the left of the screen and centred vertically.

  • Note that if you use "rewind", you can return to these initial settings at any time during this lab activity. However, if you use "reset" , you will have to re-enter all these initial settings.

If these settings have been applied, the screen should look like this.

 


 

Step 2: Given these initial conditions, make a prediction as to how you think the particle will move if it is released.  Press the "play" button  to confirm your prediction.  To see the path that the particle followed, use the "rewind" button.  Then use the "trace" option.

 

Step 3: Use "rewind" to return to the initial settings.  Repeat the previous step, but use "pause" to stop the motion at the instant the particle starts to leave the display.  View the information describing the particle in this location under "Simulation Data".

 

Step 4: Collect the following data:

 

elapsed time

charge

mass

Δ t  = ________s

q  = ____________C

m  = ___________kg

 

Express the remaining values in terms of x and y components:

  

electric field

 


 acceleration


initial velocity


final velocity


displacement

 = ___________V/m

 

( a x ,  a y ) =___________m/s 2

 

( v i x ,  v i y ) =   (150, 0) m/s

 

( v f x ,  v f y ) = ____________m/s

 

( Δd x ,  Δd y ) = __________m

 

Note that the acceleration due to gravity is ignored in this simulation.

 

Analysis

 

Self-Check

Answer the following self-check (SC) questions then click the "Check your work" bar to assess your response.

 

SC 10.

  1. Use calculations to verify the x component of the displacement.

  2. Use calculations to verify the y component of the displacement.

SC 11.  

Use calculations to verify the y component of the final velocity.

 

SC 12.  

Use calculations to verify the magnitude and the angle of the final velocity as displayed in the velocity display panel.

 

SC 13.  

Describe a situation involving gravitational fields that could produce a similar type of motion.

 

   Self-Check Answer

Your answers may be slightly different due to different time values. However, your answers will match the simulation.

 

SC10.

 

a.

Given

 

Required

The  x  component of the displacement.

 

Analysis and Solution

Since there is no  x  component of the electric field, there is no electrostatic force acting in the  x  direction. Therefore there is no acceleration in the  x  direction. In other words, the charge moves with uniform motion in the  x  direction.

 

 

Paraphrase

The  x -component of the displacement is calculated to be 351 m. This matches the value provided by the simulation.


 

b.

Given

 

Required

The  y  component of the displacement.

 

Analysis and Solution

Since the  y  component of the electric field is in the negative  y  direction, the positive particle experiences an electrostatic force in the negative  y  direction. Since this electrostatic force is unbalanced, the positive particle accelerates uniformly in the negative  y  direction.

 

 

Note: in step 3,  v i y  = 0 so the entire term is zero and is dropped for simplicity.

 

Paraphrase

The  y  component of the displacement is −137 m. This matches the value provided by the simulation.

 

SC11.

 

Given

 

Required

The  y  component of the final velocity

 

Analysis and Solution

Since the  y  component of the electric field is in the negative  y  direction, the particle experiences an electrostatic force in the negative  y  direction. Since this electrostatic force is unbalanced, the positive particle accelerates uniformly in the negative  y  direction.

 

 

Note: in step 3,  v i y  = 0 so it is dropped for simplicity.

 

Paraphrase

The  y  component of the final velocity of the particle is calculated to be −117 m/s. This matches the value provided by the simulation.

 

SC12.

 

Given


 

Required

The magnitude and the direction of the final velocity.

 

Analysis and Solution

The magnitude of the velocity can be found using the Pythagorean theorem. The direction can be found using trigonometry.

 

     

 

Paraphrase

The final velocity is calculated to be 190 m/s [38° S of E]. This matches the value provided by the simulation.

 

SC 13.  

A similar type of motion could be produced if an object were launched horizontally from the edge of a cliff. The initial velocity would be at a right angle to the gravitational field, so if the effects of air resistance could be ignored, the object would maintain its velocity in the horizontal direction while accelerating in the vertical direction. The resulting path would be the characteristic parabola of projectile motion.