q1solns - Physics 1B Electricity& Magnetism Summer...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon

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

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Physics 1B: Electricity & Magnetism Summer Session I, 2010 Quiz #1, 07/01/2010 1. A metallic object holds a total charge of- 6 . 6 × 10- 7 C. What total number of electrons does this amount of charge represent? a. 1 . 1 × 10 11 b. 1 . 6 × 10 13 c. 4 . 1 × 10 12 d. 1 . 6 × 10 12 e. 9 . × 10 9 The unit of elementary charge, e, is 1 . 6 × 10- 19 C; each electron has a charge –e. The number of electrons is (total charge)/( –e) = (- 6 . 6 × 10- 7 C)/( 1 . 6 × 10- 19 C) = 4 . 1 × 10 12 . 2. Two identical balls have the same amount of charge, but the charge on ball A is positive and the charge on ball B is negative. The balls are placed on a smooth, level, frictionless table whose top is an insulator. Which of the following is true? a. Since the force on A is equal but opposite to the force on B, they will not move. b. They will move together with constant acceleration. c. Since the force on both balls is negative they will move in the negative direction. d. Since the forces are opposite in direction, the balls will move away from each other. e. None of the above is correct. The two balls will start moving towards each other, but their acceleration will not be constant. The acceleration a of each ball is related to the magnitude of the instantaneous electrostatic force F e via F e = ma , but F e at any given instant depends on the distance of separation r of the two balls, which is decreasing as the balls roll towards each other. So as r decreases, F e increases, and the instantaneous acceleration will also be increasing (not constant). So the answer is “none of the above.” 3. A ping-pong ball covered with a conducting graphite coating has a total mass of 4 grams and carries an excess charge of –0.2 μ C. What is the magnitude and direction of the electricC....
View Full Document

This note was uploaded on 09/13/2010 for the course PHYS PHYS 1B taught by Professor Berman during the Summer '09 term at UCSD.

Page1 / 5

q1solns - Physics 1B Electricity& Magnetism Summer...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online