Midterm 2B Solutions

# Midterm 2B Solutions - PHYSICS 9C MIDTERM 2 LAST NAME FIRST...

This preview shows pages 1–3. Sign up to view the full content.

1 PHYSICS 9C MIDTERM 2 May 15, 2006 LAST NAME: FIRST NAME: SECTION: Problem 1 (2 points). If the potential profile has a form of stairs, at which points the electric field due to such profile reaches its largest values? A. At the top of stairs. B. At the bottom of stairs. C. At all points for which the potential remains flat. D. At all points for which the potential jumps. E. Electric field due to such profile will be constant and therefore does not reach its maximum anywhere. Solution: Since E(x)=-dV/dx, the electric field will go to infinity at each point where the potential jumps. Answer D. Problem 2 (2 points). If you stretch a copper wire by 3 times what happens to its resistance? A Increases 3 times B Increases 9 times C. Decreases 3 times D. Decreases 9 times E. Does not change Solution: Since R= ρ *L/A, the length L increases 3 times, and at the same time A decreases 3 times (to keep the volume of the wire V=LA constant), the resistance will increase 9 times. Answer B. Problem 3 (2 points). A charge is brought onto parallel plate capacitor, after which the distance between the plates is halved. The voltage across the capacitor is A. Doubled B. Halved C. Does not change D. Increases 4 times E. Decreases 4 times. Solution: The voltage across the capacitor V=Q/C. If the distance between the plates is halved, C new = ε 0 *A/d new = 0 *A/(d/2)=2C, i.e. the capacitance is doubled. As a result the voltage is halved. Answer B. B

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

View Full Document
2 Problem 4 (2 points). A real battery is working in a circuit. Is it possible that the voltage across it becomes larger than its EMF?
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

### Page1 / 3

Midterm 2B Solutions - PHYSICS 9C MIDTERM 2 LAST NAME FIRST...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online