PHYS202SP20082

# PHYS202SP20082 - PHYS202SP2008 Week 2 part 2 Due at 6:00pm...

This preview shows pages 1–4. Sign up to view the full content.

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Problem 25.16 Part C ANSWER: Problem 25.58 You have a lightweight spring whose unstretched length is 4.0 cm. You're curious to see if you can use this spring to measure charge. First, you attach one end of the spring to the ceiling and hang a 1.0 g mass from it. This stretches the spring to a length of 5.0 cm. You then attach two small plastic beads to the opposite ends of the spring, lay the spring on a frictionless table, and give each plastic bead the same charge. This stretches the spring to a length of 4.5 cm. Part A What is the magnitude of the charge (in nC) on each bead? ANSWER: 33.2 nC Problem 25.76 You sometimes create a spark when you touch a doorknob after shuffling your feet on a carpet. Why? The air always has a few free electrons that have been kicked out of atoms by cosmic rays. If an electric field is present, a free electron is accelerated until it collides with an air molecule. It will transfer its kinetic energy to the molecule, then accelerate, then collide, then accelerate, collide, and so on. If the electron's kinetic energy just before a collision is or more, it has sufficient energy to kick an electron out of the molecule it hits. Where there was one free electron, now there are two! Each of these can then accelerate, hit a molecule, and kick out another electron. Then there will be four free electrons. In other words, as the figure
shows, a sufficiently strong electric field causes a "chain reaction" of electron production. This is called a breakdown of the air. The current of moving electrons is what gives you the shock, and a spark is generated when the electrons recombine with the positive ions and give off excess energy as a burst of light. Part A The average distance an electron travels between collisions is . What acceleration must an electron have to gain of kinetic energy in this distance? ANSWER: 1.10×10 18 Part B What force must act on an electron to give it the acceleration found in part a? ANSWER: Part C What strength electric field will exert this much force on an electron? This is the breakdown field strength. ANSWER:

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

### Page1 / 15

PHYS202SP20082 - PHYS202SP2008 Week 2 part 2 Due at 6:00pm...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online