Physics 262 Physics for Life Sciences II Second Exam

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SECTION A1. An ionized flourine atom containing 7 protons and 8 electrons has a netcharge of(A) +1.0 C (B) −1.0 C (C) +1.6 × 10 −19 C (D) −1.6 × 10 −19 C2. I bring a negatively charged rod near (butnot touching) the bulb of an initially electricallyneutral electroscope, so that the pointerof the electroscope rises (Step 1). Keepingthe rod near the bulb, I then ground the electroscopeby touching the bulb, which resultsin the pointer falling (Step 2). In step 2,which of the following is true about the netcharges on the bulb and the pointer of theelectroscope?(A) Both the bulb and pointer have net positive charge.(B) The bulb has net positive charge and the pointer is electrically neutral.(C) The bulb is electrically neutral and the pointer has net positive charge.(D) Both the bulb and the pointer are electrically neutral.3. A square object has a charge of −2 × 10 −9 C and a round object has acharge of +1 × 10 −9 C. They are placed close to each other. Which of thefollowing figures best indicates the directions and magnitudes (indicated bythe length of the vectors) of the electric forces of the objects on one another?4. The magnitude of the Coulomb (i.e., electric) force between two pointcharges is F when they are separated by a distance d. The separationis changed so that the magnitude of the Coulomb force between them is2F . What is the new separation between the charges?(A) d d(B) √ (C) √ 2 d (D) 2d225. In a region of space, the electric potential is constant at 100 V. What is themagnitude of the force on a charge of 5 C in that region of space?(A) 500 N (B) 100 N (C) 20 N (D) 0 N
6. If there are more electric field lines going into than coming out of a Guassian(i.e., an imaginary closed) surface, this means that(A) there cannot be any positive charges enclosed by the Gaussian surface.(B) there more negative than positive charges enclosed by the Gaussiansurface.(C) there are more positive than negative charges enclosed by the Gaussiansurface.(D) there cannot be any negative charges enclosed by the Gaussian surface.7. An electron is subjected to an electric force of 1.6×10 −15 N in the downwarddirection. The electric field at the position of the electron is(A) (1.6) 2 × 10 −34 V/m, pointing upwards.(B) 1.0 × 10 4 V/m, pointing upwards.(C) (1.6) 2 × 10 −34 V/m, pointing downwards.(D) 1.0 × 10 4 V/m, pointing downwards.8. The figure below shows a charge dipole (an object with a positive chargeat one end and an equal magnitude of negative charge at the other) in aregion with electric field lines that are parallel and equally spaced fromeach other. The positive and negative charges are indicated by “+” and“-”, respectively. In which direction is the net force of the electric field onthe dipole?(A) ← (B) → (C) ↗ (D) No net force9. A 1 mF (1 × 10 −3 F) and a 2 mF (2 × 10 −3 F) capacitor are connected inparallel to a 6 V battery, as shown below. What is the total charge storedin the two capacitors?(A) 4 × 10 −3 C (B) 1.8 × 10 −2 C (C) 2 × 10 3 C (D) 9 × 10 3 C
Page 1: University of Akron July 15, 2009Ph
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Physics 262 Physics for Life Sciences II Second Exam

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