Interactions of Charges

Overview

Oftentimes called “ghost particles,” neutrinos can travel through nearly everything (the sun, the earth, you!) undetected. Because they are nearly massless, gravitational fields do not affect neutrinos; Similarly, because they are chargeless, electric and magnetic fields do not con affect neutrinos. This lack of interaction is advantageous for IceCube researchers – when they detect a neutrino, it is a straight line back to its source. On the other hand, it becomes quite difficult to detect something that’s nearly undetectable!

This lesson plan focuses on better understanding the effect of electric fields on charges. By focusing on more commonly understood electrons, protons, and neutrons, students will gain a fundamental understanding that can then be extended to other sub-atomic particles such as neutrinos.

Objectives

• Understand which charges move, which charges do not move, and why.
• Identify when an object is being charged through induction, conduction, or friction.
• Draw the movement of charges on an object that is being charged.
• Explain attraction and repulsion of charged objects.
• Make predictions for the effects of charges on a neutrino

Lesson Preparation

Gather and prepare materials:

• 1 clear plastic cup with a hole (one per student) – may want to punch a hole in the bottom of the cup before class
• ~10cm x ~30cm aluminum foil (one per student) – may want to pre-rip sheets before class
• ~ 3g of clay (one per student) – may want to tear into small balls before class
• 1 paperclip (one per student) – may want to open paperclip before class
• permanent marker (to write name on cup when finished)
• scissors
• ruler
• balloons (one per student)

Procedure

1. Lecture that covers charges of protons/electrons/neutrons, electrons can move because they’re small/light/on the outside, net charge of an object, opposite charges attract/like charges repel, charging by friction/conduction/induction, and discharging & grounding. (see attached “Presentation_Electrostatics” slides 1-14)
2. Students complete the Pre-lab questions using their knowledge from the lecture (see attached “Electroscope Lab”)
3. Students build their electroscope (see attached “Presentation_Electroscope Building”)
   Cut a piece of foil ~2 cm x ~4 cm.
   Fold the foil in half (hot dog style) and fold one end over 0.5 cm.
   Cut a small triangle along the edge to create a diamond-shaped hole after unfolding it.
   Carefully unfold the foil and cut into two separate leaves. Unfold one end of paperclip and hang the leaves on the loop. Insert the paperclip into the cup and secure it with the clay.
   Ball up the remaining foil and place on the straight end of the paperclip.
   Write your name on the cup.
4. Students explore Part 1: Charging by Induction, by charging a balloon on their hair and bring it close to the aluminum foil ball of the electroscope. Students should observe the leaves of the electroscope repelling each other. Together, model the charges using the diagram in Question 4 – For the “initial,” draw equal number of positive and negative charges distributed equally on the electroscope. For the “final,” draw equal number of positive and negative charges with the positive charges distributed equally (protons do not move) and negative charges repelling the negative balloon, collecting on the bottom leaves of the electroscope. Thus, the net negative left leaf and net negative right leaf are repelling. Students should recognize that the total number of charges has not changed, but the distribution of negative charges has.
5. Students explore Part 2: Charging by Conduction, by charging a balloon on their hair and then touching it to the aluminum foil ball of the electroscope. Students should observe the leaves of the electroscope repelling each other. Together model the charges using the diagram in Question 3 – For the “initial,” draw equal number of positive and negative charges distributed equally on the electroscope. For the “final,” draw more negative charges, as they have transferred from the balloon onto the electroscope via conduction. Thus, the net negative left leaf and net negative right leaf are repelling. In contrast to the previous example of charging by induction, students should recognize that the total number of charges has increased.
6. Students explore Part 3: Discharging and Part 4: Charging by Friction.
7. Students extend their knowledge to make a prediction for a positively charged rod brought close to the electroscope. This is a great formative assessment for students’ understanding of induction, which is usually a difficult concept.
8. Class discussion about the interaction of positive and negative charges and the lack of interaction for neutral charges. Extend this discussion to predictions for neutrinos and why IceCube might be interested in neutrinos. (see attached “Presentation_Electrostatics” slide 17 for guiding questions).

Extension

Students research other types of subatomic particles and their charges and then make predictions as to how those particles might interact with one another.

Resources

• Presentation: Electrostatics (attached)
• Electroscope Lab (attached)
• Presentation: Electroscope Building (attached)

Assessment

See #7 in the above lesson plan for a formative assessment during the lesson.

Author/Credits

This lesson was modified by Kate Miller (contact: kate.miller [at] polartrec.com) from resources produced by the Washington-Lee High School General Physics Collaboration (including Mary Clendenning and Christine Scott)